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549 AND 551 BROADWAY. 

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Matter reveals itself by its properties When matter acts, we con- 
clude that forces exist Multiplicity of the forces formerly 
admitted ; tendency to their reduction to one force in the inor- 
ganic kingdom Indestructibility of force ; its transformations 
Vital forces, their multiplicity according to the ancient 
physiologists Several vital forces are reduced to physical 
forces Of laws in physics and in physiology General theory 
of physical forces .........5 



To prove the indestructibility of forces, we must know how to 
measure them Units of heat and of mechanical work Ther- 
mo-dynamics Measure of forces in living beings Successive 
phases of the transformation of bodies ; successive development 
of force under this influence Thermo-dyuamics applied to 
living beings 13 



Origin of animal heat Lavoisier's theory The perfecting of this 
theory Estimates of the forces contained in aliment, and in 
the secreted products Difficulty of these estimates The force 



yielded by alimentaiy substances is transformed partly into heat 
and partly into work Seat of combustion in the organism 
Heating of the glands and muscles during their functions Scat 
of calorification Intervention of the causes of cooling Animal 
temperature Automatic regulator of animal temperature . . 19 



Motion is the most apparent characteristic of life ; it acts on 
solids, liquids, and gases Distinction between the motions of 
organic and animal life We shall treat of animal motion only 
Structure of the muscles Undulating appearance of the still 
living fibre Muscular wave Shock and myography Multi- 
plicity of acts of contraction Intensity of contraction in its 
relations to the frequency of muscular shocks Characteristics 
of fibre at different points of the body 27 


The function of the nerve Speed of the nervous agent Measures 
of time in physiology Tetanus and muscular contraction- 
Theory of contraction Action of the muscles .... 41 



Electricity is produced in almost all organised tissues Electric cur- 
rents of the muscles and the nerves Discharge of electric 
fishes ; old theories ; demonstration of the electric nature of 
tliis phenomenon Analogies between the discharge of electrical 
apparatus and the shock of a muscle Electric tetanus Rapidity 
of the nervous agent in the electrical nerves of the torpedo ; 
duration of its discharge 49 



Of the forms under which mechanical w<>rk presents itself Ev. IT 
machine must bo constructed with a view to the kind of work 
which it has to perform Correspondence of the lurm >! -miM-lf 
with the work which it accomplishes Theory of Borelli 
Specific force of muscles of machines; they only change the 



form of work, but do not increase its quality Necessity of 
alternate movements in living motive powers Dynamical energy 
of animated motors 59 



Each muscle of the body presents, in its form, a perfect harmony 
with the nature of the acts which it has to perform A similar 
muscle, in different species of animals, presents differences of 
form, if the function which it has to fulfil in these different 
species is not the same Variety of pectoral muscles in birds, 
according to their manner of flight Variety of muscles of the 
thigh in mammals, according to their mode of locomotion 
Was this harmony pre-established ? Development hypothesis 
Lamarck and Darwin 69 



Reasons which have caused the skeleton to be considered the least 
variable part of the organism Proofs of the yielding nature of 
the skeleton during life, under the influence of the slightest pres- 
sure, when long continued Origin of the depressions and pro- 
jections which are observed in the skeleton Origin of the 
articular surfaces Function rules the organ Variability of the 
muscular system 85 





Conditions common to all kinds of locomotion Borelli's comparison 
Hypothesis of the reaction of the ground Classification of the 
modes of locomotion, according to the nature of the point of 
resistance, in terrestrial, aquatic, and aerial locomotion Of the 



partition of muscular force between the point of resistance and 
the mass of the body Production of Useless work when the point 
of resistance is movable 102 



Choice of certain types in order to study terrestrial locomotion 
Human locomotion Walking Pressure exerted on the ground, 
its duration and intensity Re-actions on the body during 
walking Graphic method of studying them Vertical oscilla- 
tions of the body Horizontal oscillations Attempt to repre- 
sent the trajectory of the pubis Forward translation of the 
body Inequalities of its velocity during the instants of a 
pace. ........... 110 



Description of the apparatus for the purpose of studying the various 
modes of progression used by man Portable registering appara- 
tus Experimental apparatus for vertical reactions Walking 
Running Gallop Leaping on two feet and hopping on one 
Notation of these various methods Definition of a pace in any 
of these kinds of locomotion Synthetic reproduction of the 
various modes of progression 124 


Insufficiency of the senses for the analysis of the paces of the horse 
Comparison of Duges Rhythms of the paces studied by means 
of the ear Insufficiency of language to express these rhythms 
Musical notation Notation of the aniblf, of the walking pace, 
of the trot Synoptical table of paces noted according to the 
definition of each of them by different authors Instruments 
intended to determine by the graphic method the rhythms of the 
various paces, and the re-actions which accompany them . . 133 


Double aim of these experiments ; determination of the movements 
under the physiological point of view, and of the attitudes \\ith 



reference to art Experiments on the trot Tracings of the 
pressures of the feet and of the re-actions Notation of the trot 
Piste of the trot Representation of the trotting horse Ex- 
periments on the walking pace Notation of this kind of motion ; 
its varieties Piste of the walking pace Representation of a 
pacing horse 151 




Experiments on the gallop Notation of the gallop Re-actions 
Bases of support Piste of the gallop Representation of a 
galloping horse in the various times of this pace Transition, or 
passage, from one step to the other Analysis of the paces by 
means of the notation rule Synthetic reproduction of the 
different paces of the horse Modes of walking of various 
quadrupeds 164 





Frequency of the strokes of the wing of insects during flight ; acoustic 
determination ; graphic determination Influences which modify 
the frequency of the movements of the wing Synchronism of 
the action of the two wings Optical determination of the move- 
ments of the wing ; its trajectory ; changes in the plane of 
the wing ; direction of the movement of the wing . . . 180 



Causes of the movements of the wings of insects The muscles only 
give a motion to and fro, the resistance of the air modifies the 
course of the wing Artificial representation of the movements 
of the insect's wing 1 Of the propulsive effect of the wings of 



insects Construction of an artificial insect which moves hori- 
zontally Change of ]>lane in flight 196 



Conformation of the bird with reference to flight Structure of the 
wing, its curves, its muscular apparatus Muscular force of the 
bird, rapidity of contraction of its muscles Form of the bird ; 
stable equilibrium, conditions favourable to change of plane 
Proportion of the surface of the wings to the weight of the body 
in birds of different she 209 




Frequency of the movements of the wing Relative durations of its 
rise and fall Electrical determination Myographical determi- 
nation Trajectory of the bird's wing during flight Construc- 
tion of the instruments which register this movement Experi- 
mentElliptical figure of the trajectory of the point of the 
wing 226 



New determination of the trajectory of the wing Description of 
apparatus Transmission of a movement by the traction of a 
thread Instruinent and apparatus to suspend the bird Experi- 
ment on the flight of a pigeon Analysis of the curves 
Description of the apparatus intended to give indications of the 
changes in the plane of the wing during flight Relation of 
these changes of plane to the other movements of the wing . 2-11 



Re-actions of the movements of the wing Vertical re-actions in 
different species ; liori/ontal re-actions or changes in the 
rapidity of flight; simultaneous study of the two onlei 
relictions Theui\ ol the flight uf the bird -P.i.-sive and active 
parts of the wing Reproduction of the HHch.miMii ol the flight 
of the I, ml . . 204 




Fi3. 2. Theoretical representation of myograph . . . . 31 

FIG. 3. Marey's myograph .32 

FIG. 7. .Arrangement of a muscular bundle between two myo- 

graphical clips . . 37 

FIG. 19. Experimental shoe, intended to show the pressure of the 

foot on the ground, with its duration and its phases . 113 

FIG. 42. Experimental apparatus to show the pressure of the 

horse's hoof on the ground 148 

FIG. 43. Apparatus to give the signals of the pressure and rise of 

the horse's hoof . . . . . . . .149 

FIG. 26. Apparatus to determine the speed of walking at every 

instant ... . . . . 122 

FIG. 27. Runner provided with the apparatus intended to register 

his different paces 126 

FIG. 28. Instrument to register the vertical re-actions during the 

various paces 127 

FIG. 44. Figure to represent a trotting horse, furnished with 
the different experimental instruments ; the horseman 
carrying the register of the pace. On the withers and 
the croup are instruments to show the re-actions . . 150 

FIG. 93. Apparatus for the purpose of experimenting on the con- 
traction of the thoracic muscles of the bird . . . 229 

FIG. 99. Buzzard flying, with the apparatus for giving signals of 

the movements of the extremity of its wing . . 241 

FIG. 103. General arrangement of the recording instrument]; apigeon 

attached to it, and conveying signals . . . . 248 

FIG. 104. Suspension of the bird in the apparatus .... 250 

FiG. 109. Apparatus to examine the movements of the wing, and 

the changes in its plane .... . 260 

FIG. 21. Transmission of an oscillatory movement to the regis- 
tering apparatus .... 



FIG. 24. Showing two successive positions of the arm of the instru- 
ment, and the COTTespondiug positions of the tracing 

points of the levers 120 

FIG. 98. Elastic point, tracing on a piece of smoked glass . . 239 
FIG. 102. Transmission of a to-and-fro movement by means of a 

simple traction thread 245 


FIG. 1. Showing the transformation of the electricity of a coil 

into mechanical work, heat, light, and chemical action . 10 
FIG. 6. Appearance presented by the waves in a muscular fibre . 3G 
FIG. 9. Transformation of heat into work by a strip of india- 
rubber 39 


FIG. 84. Artificial representation of the movements of the insect's 

wing 199 

FIG. 85. Changes in the plane of the insect's wing . . . . 200 
FIG. 87. Artilicial insect, to illustrate its flight .... 202 
FIG. 88. Arrangement of the artificial insect, so as to obtain the 

hovering motion or the ascending flight . . . . 205 


FIG. 90. Instrument to illustrate the hovering of the bird . .217 
FIG. 91. The same, explaining the upward turn . . . . 218 
FIG. 92. ,, downward ditto . . .219 


FIG. 13. Skeleton of a flamingo (after Alph. Millie-Edwards; the 

wing is very large, the sternum very short and deep, 
which indicates the size and the shortness of the pectoral 
muscles . . . . . . . . . . 72 

FlG. 14. Skeleton of a penguin: sternum very long, wing very 

short .......... 73 

FlO. 15. Ski h 'ton df the wing and sternum of the sea swallow 
(Ilirundo marina); showing tin- extreme .short m->s of 
the sternum, and the great length of the wing . . . 7t 

Fi<:. 89. Different curves in tin: wing of the liinl ait vaiions ji.i!^ ot 

its length . . 210 

FH;. 117. Active and passive parts of tho bird'i wing . . . . 'J7<> 

Flu. > S J. -Minetuiv n| th. in - t' \\ ing . . . . 1'Jb 



FIG. 16. Muscles of the thigh in man . . , . . . 76 

FIG. 17. Muscles of the thigh of the magot 77 

FIG. 18. Muscles of the thigh of the coaiita . , . . . 78 


FIG. 8. Two determinations of the speed of the muscular wave . 33 
FIG. 10. Determination of the speed of the nervous agent in man . 43 
FIG. 12. Measure of the time which elapses between the excitation 

of the electric nerve, and the discharge of the torpedo . 58 
FIG. 82. Determination of the direction of the movements in an 

insect's wing 195 

FlG. 94. Experiment to determine by the electric and myographic 
methods at the same time, the frequency of the move- 
ments of the bird's wing, and the relative duration of 

its elevation and depression 230 

FlG. 26. Determination of the rapidity of walking at various 

instants, by means of a chronographic tuning fork . 122 


FIG. 34. Notation of a tracing of man's mode of walking . . 133 
FIG. 35. Synoptical notation of the four kinds of progression used 

by man 134 

FIG. 36. Notations of the gallop (man) 134 

FIG. 37. (Upper line) notation of a series of jumps oil two feet. 

(Lower line) notation of hops on right foot . . . 135 


FIG. 38. Notation of a horse's amble 142 

FIG. 39. Notation of the horse's walking pace . . . 143 

FIG. 51. Notation of the walking pace, with predominance of the 

lateral pressures . . . . .160 
FIG. 45. Graphic curves and notation of the horse's trot . . . 153 

FIG. 40, Notation of a horse's trot 144 

FIG. 46. Notation of the irregular trot . . . 156 

FIG. 41. Synoptical notations of the paces of the horse, according 

'to various writers. 

No. 1. Amble, according to all writers. 
.. f Broken amble, according to Merche. 

\ High steps, according to Bouley. 
( Ordinary step of a pacing horse, according to Magure. 
No. 3. \ Broken amble, according to Bouley. 
( Traquenade, according to Lecoq. 



No. 4. Normal walking pace, according to Lccoq. 

No. 5. Normal walking pace (Bouley, Vincent ami Coition 

Sollcyscl, Colin). 

No. 6. Normal walking pace, according to Raabc. 
No. 7. Disconnected trot (trot de coursier). 
No. 8. Ordinary trot. (In the figure, it is supposed that the 
animal trots without leaving the ground, which occurs but 
raivly. The notation only takes into account the rhythm 
of the impacts of the feet). 
No. 9. Norman pace, from Lecoq. 

No. 10. Traqueuade, from Mcrche 146 

FIG. 56. Gallop in three-time 166 

FIG. 62. Notation of the gallop in four-time 170 

FIG. 63. Notation of full gallop ; re-actions of this pace . . 171 

FIG. 64. Transition from the walk to the trot 174 

FIG. 65. Transition from the trot to the walk . . . .174 
FIG. 66. Transition from the trot to the gallop . . . . . 174 
FIG. 67. Transition from the gallop to the trot .... 174 
FIG. C8. Notation rule, to represent the different paces . . . 175 
FIG. 69. Notation rule forming the representation of the gallop in 

three-time . 176 


FIG. 52. Piste of the walking pace, after Vincent ami GoifTou . . 162 

FIG. 53. Piste of the amble, after Vincent and Goi (foil . . . 162 

FIG. 47. Piste of the trot according to Vincent and Goiffon . . 1:"7 

FIG. 57. Piste of the short gallop in three-time .... 167 
FIG. 58. Piste of Eclipse's gallop, from Cornicu. The prints of the 

hind-feet arc very far before those of the fore-feet . . 167 


Fie. 54. Representation of the horse at a walking pace . . . 163 
FIG. 48. Horse trotting with a low kind of pace . . . . 157 
FIG. 49. Horse at full trot. The dot placed in tiie notation corre- 
sponds with the attitude represented .... 158 
FIG. 59. IIor>e galloping in the tirst. time (right foot advancing), 

the Mi fool "iily on tli^ ground ... . . 168 

1 ic. 60. Horse galloping in (lie second lime (right foot forward) . 169 

I'm. 61. Horse galloping iu the third time (right foot forward) . 169 




4. Character of the shock according to the degree of fatigue 

of the muscle . . . . . . . 34 

FIG. 5. Successive transformations of the shock of a muscle be- 
coming gradually poisoned by veratrine. Underneath 
and on the left of the figure are shown the first effects 
of the poison ........ 35 

FIG, 11. Gradual coalescence of the shocks produced by electric 

excitations of increasing frequency 46 


FIG. 20. Tracings of the impact and the pressure of the two feet in 

our ordinary walk . . . . . . .114 

FIG. 22. Tracings of the oscillations of the body during walking . 117 
FIG. 25. Tracing of the impact and rise of the right foot, furnished 
by a lever subjected at the same time to 10 vibrations 
per second ......... 121 

Fro. 20. Tracing produced by walking upstairs .... 128 

FIG. 30. Tracing produced by running (in man) . . . . 128 

FIG. 31. Man galloping (right foot foremost). Step-curves and re- 
actions. There is an encroachment of one curve over the 
other, and then a suspension of the body . . . 131 
FIG. 33. Series of hops on the right foot. The duration of the 
time of suspension remains evidently constant, even 
when that of the pressure of the foot varies . . . 132 
FIG. 32. Leap on two feet at once 131 


FlG. 50. Tracing and notation of the walking pace, with equal 

pressures of the feet, both diagonally and laterally . . 160 

FIG. 45. Tracing and notation of the trot 153 

FIG. 55. Tracing and notation of the gallop in three-time . . . 165 


FIG. 70. Showing the frequency of the strokes of the wing of a 

drone-fly and a bee ....... 183 

FIG. 72. Graphic tracing of the middle portion of the course of a 

bee's wing 189 



FIG. 73. Tracing of the middle zone of a humming-bird moth . 190 

FIG. 74. Tracing of the course of a wasp's wing showing the upper 

part of the curve 190 

FIG. 75. Tracing of the course of a wasp's wing : lower loops . 191 

FIG. 77. Tracing obtained from a bee's wing in a plane tangential 

to the cylinder 192 

FIG. 78 and 79. Tracing of a wasp's wing, compared with a Wheat- 
stone's rod . 192, 193 

FIG. SO. Tracing of the wing of a humming-bird moth (lower 

border) 193 

FIG. 81. Tracing of the wing of a tired humming-bird moth . . 194 


FIG. 95. Myographical tracing to determine the frequency of the 

strokes of the wing in different species . . . . 232 
FIG. 96. Differences of frequency and of amplitude in the strokes 

of a pigeon's wing 234 

FIG. 105. Tracing of different movements of the pigeon's wing . . 253 
FIG. 106-107. Construction of the trajectory of a pigeon's wing, 254, 255 
FIG. 110. Simultaneous tracing of tl\e different movements of a 

buzzard's wing 262 

FIG. 111. Inclination of the plane of the wing, with reference to the 

axis of the body during flight 263 

FIG. 113. Vertical oscillations of the bird during flight . . .266 
Fio. 114. Relation of oscillations with muscular acts . . . 268 
FIG. 115. Simultaneous tracing of two kinds of oscillation in the 

buzzard 271 


FIG. 23. Attempt to illustrate, by means of a metallic wire, the 

sinuous trajectory passed through by the pubis . . 119 
FIG. 71. Appearance of a wasp the tips of whose wings have been 

gilded 187 

FIG. 86. Trajectory of an insect's wing 201 

FIG. 100. Elliptical course of the point of a bird's wing . . . 242 

FIG. 76. Tracing of a vibrating Wheatstone's rod .... l;i] 

FIG. 79. Do. tipped with a wasp's wing l'.i:j 

FIG. 101. Ellipse traced by a WlieatM<nu-'s r< d on a revolving 

cylinder 243 




LIVING beings have been frequently and in every age 
compared to machines, but it is only in the present day 
that the bearing and the justice of this comparison are fully 

No doubt, the physiologists of old discerned levers, pulleys, 
cordage, pumps, and valves in the animal organism, as in the 
machine. The working of all this machinei-y is called Animal 
Mechanics in a great number of standard treatises. But these 
passive organs have need of a motor ; it is life, it was said, 
which set all these mechanisms going, and it was believed 
that thus there was authoritatively established an inviolable 
barrier between inanimate and animate machines. 

In our time it is at least necessary to seek another basis 
for such distinctions, because modern engineers have created 
machines which are much more legitimately to be compared 
to animated motors ; which, in fact, by means of a little com- 
bustible matter which they consume, supply the force requisite 
to animate a series of organs, and to make them execute the 
most various operations. 

The comparison of animals with machines is not only legiti- 
mate, it is also extremely useful from different points of view. 
It furnishes a valuable means of making the mechanical 
phenomena which occur in living beings understood, by 
placing them beside the similar but less generally known 
phenomena, which are evident in the action of ordinary 


machines. In tlio course of tliis Look, we shall frequently 
borrow from pure mechanics the synthetical demonstrations 
of the phenomena of animal life. The mechanician, in his 
turn, may derive useful notions from the study of nature, 
Avhieh will often show him how the most complicated problems 
may be solved with admirable simplicity. 

Animr.l mechanics is a wide fiold for exploration. To 
every function, so to speak, a special machinery is attached. 
The circulation of the blood, the respiration, &c., may and 
ought to be treated separately, so that we shall limit this work 
to the study of one single, essentially mechanical, function, 
locomotion in the various animals. 

It is easy to demonstrate the importance of such a subject as 
locomotion, which, under its different forms, terrestrial, aquatic, 
and aerial, has constantly excited interest;. Whether man has 
endeavoured to utili/e to the utmost his own motive power, 
and that of the animals ; whether he has sought to extend 
liis domain, to open a way for himself in the seas, or to rise 
into the air, it is always from nature that he has drawn his 
inspirations. AVe may hope that a deeper knowledge of the 
dillereiit modes of animal locomotion will be a point of 
departure for fresh investigations, whence fuither progress 
will result. 

Every scientific research has a powerful attraction in itself; 
the hope of reaching the truth suffices to sustain those who 
pursue it, through all their efforts ; the contemplation of the 
laws of nature has been a great and noble source of enjoy- 
ment to those who have discovered them. But to humanity, 
science is only the means, progress is the aim. If we can 
show that a study may lead to some useful application, wo 
may induce many to pursue it, who would otherwise merely 
follow it from afar, with the interest of curiosity only. 
Without pretending to recapitulate here all that lias been 
gained by the study of nature, wo shall endeavour to set 
forth what may be gained by studying it still further, and 
with more care. 

Terrestrial locomotion, that of man, and of the great mam- 
mals, for instance, is ver}' imperfectly understood as yet. If 
\M knew under what conditions the maximum of speed, force, 


or labour wliichthe living being- can furnich, may be obtained, 
it would -put an end to much discussion, and a great deal of 
conjecture, which is to be regretted. A generation of men 
would not be condemned to certain military exercises which 
will be hereafter rejected as useless and ridiculous. One 
country would not crush its soldiers under an enormous 
load, while another considers that the best plan is to give 
them nothing to cany. We should know exactly at what 
pace an animal does the best service, whether he be required 
for speed, or for drawing loads ; and we should know what 
are the conditions of draught best adapted to the utilization 
of the strength of animals. 

It is in this sense that progress is being made ; but if we 
complain with reason of its slow advance, we must only 
blame our imperfect notion of the mechanism of locomotion. 
Let this study be perfected, and then useful applications of it 
will soon ensue. 

Man has been manifestly inspired by nature in the con- 
struction of the machinery of navigation. If the hull of 
the ship is, as it has been justly described, formed on the 
model of the aquatic fowl, if the sail has been copied from the 
wing of the swan inflated by the wind, and the oar from its 
webbed foot as it strikes the water, these are but a small part 
of nature's loans to art. More than two hundred years ago, 
Borelli, studying the stability and displacement of fish, traced 
the plan of a diving-ship constructed upon the same principle 
as the formidable Monitors which made their appearance in 
the recent American war. 

In modern navigation the dynamic question still leaves 
several points in obscurity. What form should be given to a 
ship so as to secure its meeting with the least possible resist- 
ance in the water? What propeller should be chosen in 
order to utilize the force of the machine to the best advan- 
tage ? The most competent men in such matters avow that 
these problems are too complex to admit of the conditions 
most favourable to the construction of ships being determined 
by calculation. Must we wait until empiricism, by dint of 
ruinous guesses, shall have taught us how a problem of 
which nature offers us such diverse solutions, should be 


solved? Ingenious constructors have already attempted to 
imitate the natural propellers ; they have fitted up small boats 
with machinery which works like the tail of a fish, oscillating 
with an alternate motion. And it has been found that this 
apparatus, although still imperfect, already constitutes a 
powerful propeller, which will perhaps be preferred hereafter 
to all those which have hitherto been used. 

Aerial locomotion has always excited the strongest curiosity 
among mankind. How frequently has the question been 
raised, whether man must always continue to envy the bird 
and the insect their wings ; whether he, too, may not one day 
travel through the air, as he now sails across the ocean. 
Authorities in science have declared at different periods, as 
the result of lengthy calculations, that this is a chimerical 
dream, but how many inventions have we seen realised which 
have also been pronounced impossible. The truth is, that all 
intervention by mathematics is premature, so long as the 
study of nature and experiment have not furnished the precise 
data which alone can serve as a sound starting point for 
calculations of this kind. 

We shall then attempt to analyse the rapid acts which are 
produced in the flight of insects and of birds ; afterwards we 
shall endeavour to imitate nature, and we shall see, once 
more, that by seeking inspiration from her we have the 
best chance of solving the problems which she has solved. 

We may even now affirm, that in the mechanical actions of 
terrestrial, aquatic, and aerial locomotion, there is nothing 
which can escape the methods of anaLysis at our disposal. 
Would it be impossible for us to reproduce a phenomenon 
which we understand ? We will not carry our scepticism 
BO far. 

It was considered for a long time that chemistry, all- 
powerful when it was a question of decomposing organic 
substances, would always remain incapable of reproducing 
them. What has become of this disheartening prediction ? 

We hope that the reader who follows the experimental 
researches detailed in this book will draw from them this 
conviction, that many of the impossibilities of the present, 
need only a little time and much effort to become realities. 




Of forces in the inorganic kingdom and among organised beings Matter 
reveals itself by its properties When matter acts, we conclude that 
forces exist Multiplicity of forces formerly admitted; tendency to 
their reduction to one force in the inorganic kingdom Indestruc- 
tibility of force ; its transformations Vital forces, their multiplicity 
according to the ancient physiologists Several vital forces are 
reduced to physical forces Of laws in physics and in physiology- 
General theory of physical forces. 

WE know matter only by its properties, which we could not 
conceive of apart from matter. The word property does not 
answer to anything real : it is an artifice of language ; thus, the 
expressions, weight, heat, hardness, colour, &c., attributed to 
various bodies in nature, mean that these bodies manifest 
themselves to our senses by certain effects which have been 
made known to us by daily experience. 

When matter acts, that is to say, when it changes its state, 
there occurs what we call a phenomenon, and by a new appli- 
cation of language we call the unknown cause which has 
produced this phenomenon, Force. A body which falls, a 
river which flows, a fire which warms us, the lightning which 
flashes, two bodies which combine, &c., all these correspond to 
manifestations of forces which we call gravity, mechanical 
force, heat, electricity, light, chemical affinities, &c. 

In the first ages of science the number of forces was almost 
infinitely multiplied. Each particular phenomenon was re- 
garded as the manifestation of a special force. But by degrees 
it was recognised that divers manifestations might result from 


a single cause ; and thenceforth the number of forces which 
were admitted diminished considerably. 

\\Viuht and attraction were reduced to one and (lie same 
force by Newton, who recognised, in the falling of the apple 
to the ground, and the retention of the star in its orbit, the 
effects of an identical cause universal gravitation. Amj ere 
reduced magnetism to a manifestation of electricity. Light 
and heat have long since been regarded as manifestations of sin 
identical force, an extremely rapid vibratory motion imparted 
to the ether. 

In our own time a grand conception has arisen, once more 
to change the face of science. All the forces of nature are 
reduced to one only. Force may assume any appearance ; it 
becomes, by turns, heat, mechanical work, elcc tricity, light ; 
it gives rise to chemical combinations or decompositions. 
Occasionally, force seems to disappear, but it has only hidden 
itself; we can find it again in its entirety, and make it pass 
anew through the cycle of its transformations. 

Force, which is inseparable from matter, is, like it, inde- 
structible, and to both the absolute principle, that in nature 
nothing is created and nothing is destroyed, is applicable. 

Before we enter upon a detailed exposition of this great 
conception of the conservation of force and its transformations 
in the inorganic "world, let us see whether any analogous 
.generalisation has been arrived at in the science of organised 

The living being, in its manifestations of sensibility, intelli- 
gence, and .-i < ntaneity, shows itself to be so different from 
the inert and passive bodies of inorganic nature; the genera- 
tion and the evolution of animals are so peculiar to them- 
selves ; that the earliest observers traced an absolute boundary 
between the two kingdoms of nature. 

Particular forces were imagined, to which each of the 
normal phenomena of life was attributed, vhile others, like 
malignant genii, presided over the production of the maladies 
by which everything that has life may be attacked. 

The. complexity of the phenomena of'lil'e hindered observers 
for a long time i'nmi dihcerning the link which united them, 
and pieventtd their referring to one and the same cause these 


manifold effects, and thus reducing the number of forces 
which had at first been admitted. Man ended by taking 
the fictions of his imagination for realities. Little by little, 
the charm of the unintelligible exercising fascination over 
him, he at last denied that physical laws had any in- 
fluence upon living beings. This extravagant mysticism 
represented certain animals as capable of withdrawing them- 
selves from the influences of weight ; according to it, animal 
heat was of another essence than that of our hearths ; subtle 
and impalpable spirits circulated in the vessels and the nerves. 

Time has not even yet disposed of all these absurdities ; 
but we can prove that the science of life tends at present 
to undergo a transformation as complete as that of the phy- 
sical sciences, whose development we have just sketched. 
Physiology, guided by experience, seeks and finds the physical 
forces in a great number of vital phenomena ; every day sees 
an increase in the number of cases to which, we can apply 
the ordinary laws of nature. That which escapes them 
remains for us the unknown, but no longer the unknowable. 
Among the phenomena of life, those which are intelligible 
to us are precisely of the physical or mechanical order. 

In the living organism we shall fiud those manifestations 
of force which are called heat, mechanical action, electricity, 
light, chemical action ; we shall see these forces transforming 
themselves one into the other, but we must not hope to arrive 
immediately at the numerical determination of the laws which 
regulate the transformations of these forces. The animal 
organism does not lend itself to exact measurements, its com- 
plexity is too great for valuations, to which physicists attain 
with great difficulty by making use of the simplest machines. 

Each science, according to its degree of complexity, is 
approaching more or less surely to the mathematical precision 
at which it must arrive sooner or later. A law is only the 
determination of numerical relations between different phe- 
nomena; there is then no perfect physiological law. In the 
phenomena of life it is scarcely possible to determine and to 
foresee anything except the manner in which the variation will 
be produced. Hitherto, the physiologist has reached only that 
degree of knowledge which the astronomer would possess, who 


knew, for instance, that the attraction between t\vo heavenly 
bodies diminishes when their distance increases, but who had. 
not yet determined the law of inverse proportionality to the 
square of distances. Or, he is like the physicist who has proved 
that compressed gases diminish in volume, but who has not 
found the numerical relation bet\veeu their volume and the 

Without doubt, however, there are numerical relations 
between the phenomena of life ; and we shall arrive at the 
discovery of them more or less speedily, according to the 
exactitude of the methods of investigation to which we have 

If physicists had limited themselves to establishing that 
bodies dilate as they become heated, and if they had not 
sought to measure the temperature of 'those bodies and the 
volume which they assume with each variation of the temper- 
ature, they would have had only an imperfect idea of the 
phenomena of the dilatation of bodies by heat. For a long 
time physiologists confined themselves to pointing out that 
such or such an influence augments or diminishes the force of 
the muscles, causes the rapidity of their motions to vary, 
increases or diminishes sensibility and motive power. Science, 
in our time, has become more exacting, and already the 
rigorous determination of the intensity and duration of certain 
acts, of the form of different movements, of the relations of 
succession between two or several phenomena, the precise 
estimation of the rapidity of the blood, or of the transference 
of the sensitive or motive nervous agent; all these exact 
measures introduced into physiology, lead us to hope that 
from more scrupulous measurement better formulated laws 
\\ill soon result. 

In the comparison which we are about to make between 
the physical forces and those which animate the animal 
organism, we shall take it for granted that the fundamental 
notions recently introduced into science, and by which all those 
forces tend to reduce themselves to one only, that which 
engenders motion, are known; and shall, therefore, confine 
ourselves to a rapid sketch of the new theory. 

The value of a theory depends on the number of the facts 


which it embraces ; that of the unity of the physical forces 
tends to absorb them all. From the invisible atom to the celes- 
tial body lost in space, everything- is subject to motion. Every- 
thing gravitates in an immense or in an infinitely little orbit. 
Kept at a definite distance one from the other, in proportion 
to the motion which animates them, the molecules present 
constant relations, which they lose only by the addition or the 
subtraction of a certain quantity of motion. In general, 
increase of motion enlarges the orbit of the molecules, and 
widening their distance from each other, increases the volume 
of the bodies. By this rule, heat is proved to be a 
source of motion. Under its influence the molecules, becom- 
ing more and more separated, cause bodies to pass from 
solid to liquid, and then to a gaseous state. These 
gases become indefinitely dilated by the addition of fresh 
quantities of heat. But that force which lends extreme 
rapidity to the motion of the molecules, that force which is 
admitted in theory is rendered tangible by experiment ; its 
intensity is measured by opposing to the dilatation of a body 
an obstacle which it will have to surmount. Thus it is that 
the molecules of gases or vapours imprisoned in the cylinder 
of machines, communicate to the partitions and to the piston 
the pressure which is employed in producing action by 
machinery. This mechanical action is, in its turn, trans- 
formed into heat if the conditions of the experiment be re- 
versed ; if, for example, an external force, thrusting back 
the piston of an air-pump, restrains the molecular motions by 
violent compression. 

The new theory has thrown light upon certain hypotheses, 
those, among others, which claimed admission for the latent 
heat of fusion, or of vaporisation of bodies, the latent heat of 
dilatation of gases. It has suppressed others ; for instance, 
the discovery of atmospheric pressure has banished the 
hypothesis which has now become ridiculous, that nature 
abhors a vacuum. 

Although the theory accommodates itself with less ease to 
the interpretations of luminous and electric phenomena, it 
admits, according to the great analogy between these phe- 
nomena, and heat, of supposing that they themselves are only 



manifestations of motion. Besides, the transformation of 
motion into heat, into electricity, into light, may be proved 

Fig. 1 represents the details of the experiment. 

FIG. 1. Showing the transformation of the electricity of ,1 battery into mecha- 
nical action, into huat, Ii 'ht, and chemical action. 

Various instruments are so arranged upon a table that an 
electric current, engendered by a battery I', may be made to 
pass through them.* The current is conducted in an elliptic 
circuit, on a small square board, represented in the centre of 
the figui-e. This circuit is formed of a thick copper wire; 
at certain points this wire is interrupted and dipped into 
cups of mercury, from which other wires communicate with 
the various apparatus through which the current is to be con- 
ducted. In Fig. 1, the metallic bridges 1, 2, 3, 4, 5, connect 
the cups of mercury, and form a complete circuit, which the 
current may traverse without passing through the various 
apparatus placed ai'ound it. 

If we take away loop No. 1, the current which passed 
through that loop is forced to traverse the elliptical circuit 
without passing through the surrounding apparatus. But if we 

Instead of tlie single element represented in the Figure, it is necessary 
to employ a series <>f Ijiiiisen's cells, to realise the experiments perfectly. 


afterwards remove loop No. 2, the current must traverse the 
apparatus M, which is an electro-magnetic motor. This appa- 
ratus will begin to move and will produce mechanical action. 

Let us at the same time remove loop No. 3, the current 
must also traverse a registering thermometer. [That 
instrument is constructed as follows. It is a sort of Reiss' 
thermometer, formed of a spiral of platinum, which the current 
traverses, and which is conducted into a flask full of air. 
Under the influence of the heating of the spiral by the current 
which traverses it, the air in the bottle dilates, and passes, 
through a long tube, into the registering apparatus. The 
Litter is composed of a drum of metal, closed on the upper 
side by a membrane of india-rubber. When the air pene- 
trates into the drum, the membrane swells, and lifts up a 
registering lever, which traces on a turning cylinder E, a curve 
whose elevations and depressions correspond with the rise and 
fall of the temperature.] 

By removing loop No. 4, we force the current to traverse 
an apparatus L, with carbon points, in which electricity 
gives birth to the bright light with which every one is 
acquainted. When it passes through the voltameter V, the 
current produces decomposition of the water. The intensity 
of the current is measured by the quantity of water decom- 
posed, i.e., by the volumes of hydrogen and oxygen which 
are disengaged. 

We see, in the first place, by means of this apparatus, 
that electricity can become successively mechanical work in the 
motor M, heat in the spiral of the thermometer T, light 
between the ca,rbon points L, and chemical action in the 
voltameter V. 

But we also recognise that the electricity which imdergoes 
one of those metamorphoses is taken away from the current 
whose energy is thus diminished. If, for example, we make 
the motor M work, we shall see that the register marks a 
diminution of heat in the thermometer. If we stop the 
electro-magnetic motor with the hand, an increase in the 
temperature becomes immediately apparent ; the registered 
curve rises. 

When the electro-magnetic motor is working, we see the 


intensity of the light diminish, and the decomposition of 
the water in the voltameter grow less. All these phenomena 
resume their pristine energy as soon as we suppress the 
production of mechanical action. 

During this time, all the force expended in these various 
forms of apparatus is disengaged from the battery under the 
influence of a chemical action: the transformation of a certain 
quantity of zinc into sulphate of zinc. Thus, in the furnace 
of a steam engine, the combustion of the coal, that is to say, 
the oxidation which transforms carbon into carbonic acid 
disengages heat, which is afterwards converted into work. 

But this force, disengaged from bodies, was contained in 
them when the zinc was in the condition of metal, and the 
carbon in the state of coal; these bodies had employed in 
their formation the same quantity of force which they 
have yielded up in passing into another condition. Tims it 
would be necessary to restore to the sulphate of zinc and to 
the carbonic acid as much electricity or heat as they have 
thrown out, in order to reproduce the metallic zinc or the 
carbon in a pure state. 

According to the modern theory, force which manifests 
itself at a given moment is not created, but only rendered 
sensible, from being latent. 

Here in tension is that potential force, which, stored up in 
a body, waits the opportunity to manifest itself. Thus a 
sti-etchcd spring will at the end of an indefinite time give back 
the force which has been used to stretch it ; and a weight, 
lifted to a certain height, will restore, the instant it fulls, 
the work that has been employed upon raising it. 




To prove the indestructibility of forces, we must know how to 

them Units of heat and of mechanical work Thermo-dynamics 
Measure of forces in living beings Successive phases of the trans- 
formation of bodies ; successive throwing off of force under this iuilu- 
ence Thermo-dynamics applied to living beings. 

WE have just seen that force, in the different states which 
it presents, may be now latent, or potential, or again in action, 
in the form of heat, electricity, or mechanical activity. 

To follow this force through all its different transformations, 
to establish that no portion of it is lost, a means of measuring 
it under all its forms is necessary. The chemist can prove 
the indestructibility of matter, by showing, with a balance, 
that a gramme of matter will preserve its weight through all 
the changes of condition that can be imposed upon it. Let 
that matter be weighed in the liquid state, in the solid state, 
or in the gaseous state, the. weight of a gramme will always 
be found under the most various volumes and aspects. 

A measure is then necessary for the different manifestations 
of force. Every quantity of heat, of electricity, or of mechani- 
cal work ought to be compared with a particular unit, as every 
weight ought to be compared with the unit of weight. 

Unit of heat. The sensations of heat and cold which we 
experience at the contact of different bodies do not correspond 
with the quantity of heat which those bodies contain. Ther- 
mometrical apparatus are not in a condition to give us the 
measure of the quantities of heat, since different bodies, 
presenting to our senses and by the thermometer the same 
temperature, may yield very unequal quantities of heat. But, 
to warm the same weight of a body to the same number of 
degrees, the same quantity of heat will alwa}'s be necessary. 

Now, according to the agreement which has been come to 
in France and in many other countries, the unit of heat or 


calorie is the quantity of heat necessary to raise a kilogramme 
of water from zero to one degree centigrade. 

Unit of work. Mechanical force has been accurately de- 
fined only since the notion of work has been introduced into 
science. The unit of mechanical work admitted iu France 
is the kilogrammetre ; that is to say, the force necessary to 
raise the unit of weight the kilogramme to the uuit of 
height, the metre. 

Electric force is measured by one of its effects, the decom- 
position of water, for it is demonstrated that to decompose 
the same volume of water the same quantity of electricity will 
always be requisite. 

These measures of forces in action furnish, in their turn, 
the means of estimating the quantity of potential force con- 
tained in a body. Thus, it will be demonstrated that in a 
kilogramme of coal, and in the quantity of oxygen necessary 
to transform that coal into carbonic acid, there were in tension 
7000 units of heat, since by combining all the heat disen- 
gaged by combustion, a mass of water of 7000 kilogrammes 
shall have been heated. 

But a substance which burns is not alwaj'S completely 
oxidized ; hence, it does not put in action the totality of the 
force which it contained iu tension. A kilogramme of carbon, 
for example, may undergo only a first degree of oxidation, and 
thus becoming oxide of carbon it yields only 5000 units of 
heat. This oxide of carbon burning in its turn, and becoming 
carbonic acid, will then yield only the remaining 2000 units 
of heat. 

Transformation of physical forces takes place, as we have 
said, without any loss of the transformed force. To demon- 
strate this, it must be proved that a certain number of units 
of heat transformed into work, will furnish a constant number 
of kilogrammetres, and inversely, that this work in becoming 
heat again, will restore the primitive number of units of heat. 

The science which explains the relations between heat and 
mechanical work, and fixes the value of the mechanical cqitirnlent 
(>f licut is called thermo-dynamics. This conception, which is 
the complement of the theory of the transformation of forces, 
and which proves that in their transformation they lose 


nothing of their value, is justly considered the most remarkable 
of modern times. 

Partly seen by Sadi-Carnot, clearly formulated by R. Mayer, 
demonstrated brilliantly by the experiments of Joule, the 
notion of the equivalence of forces is now admitted by all 
physicists. Each day furnishes a fresh confirmation of this 
doctrine, and leads to greater precision in the determination of 
the mechanical equivalent of heat. The value now generally 
admitted for that equivalent is 425, that is to say, that work 
equal to 425 kilogrammetres must be transformed into heat 
to obtain a unit, and inversely, that the heat capable of heat- 
ing to one degree one kilogramme of water at zero, if it be 
transformed into work, can, in its turn, lift a weight of 425 
kilogrammes one metre.* 

But one restriction must be placed upon the estimation 
of thermo-dynamic transformations. Caruot suspected, and 
Clausius had clearly established that in the case of heat being 
employed to produce work, the heat cannot transform itself 
altogether, and that the greater part remains still in the state 
of heat ; while in the inverse operation the whole of the work 
applied to that effect may be transformed into heat. This 
does not exclude the law of equivalence, of which we have 
just spoken; for if it be true that, in a steam engine for 
instance, there is only to be found under the form of work a 
email quantity, about 1 2 of the heat produced by the fur- 
nace, it is no less true that the quantity of heat which has 
disappeared furnishes in work the exact number of kilo- 
grammetres which corresponds to its mechanical equivalent. 

These notions had no sooner been introduced into science 
than the physiologists endeavoured to use them for the 
clearing up of the obscure question of heat and work pro- 
duced by animals. The assimilation of living beings to 
thermal machines was already in the state of vague con- 
ception. We shall see what light has been thrown upon it 
by the new theory. 

* Some experiments made by Regiiault on the rapidity of sound, and 
on the expansion of gases, give as the true value of the equivalent the 
number 439. 


"We have said tliat forces are produced within the organism. 
All living beings give out heat and produce work. The- 
disengagement of these forces is caused by the chemical 
transformation of food. 

In the living being it is possible to measure approximately 
the quantities of heat and work produced, and even to estimate 
the quantity of force contained in f-od ; in order to do this 
it is sufficient to apply the methods which physicists have 
employed in the estimation of inorganic forces. 

Thus, a man placed for some time in a bath will yield to 
the water a certain number of units of heat, which may be 
easily measured. Applied to the moving of a machine, the 
force of a man or an animal will produce a number of kilo- 
grammetrea no less easily to be measured. If the aliment be 
subjected to the experiments which determine the heating 
power of different combustibles, it will be found that each of 
them contains a certain quantity of potential force. Favre and 
Silbennann have supplied most valuable information, attained 
by great labour, on this point ; and Fraukland has continued 
their investigations. We no\v know the calorific power of 
almost all the alimentary substances, it is, therefore, possible 
to calculate what free force their complete oxidation will yield 
either under the form of heat or under the form of work. 

But, as we have seen with respect to combustibles employed 
for industrial purposes, the oxidation is not always complete. 
Coal partially consumed, gives solid or gaseous residues, 
such as coke and oxide of carbon, which, being oxidized in 
a more complete manner, furnish a certain quantity of heat. 
In the same way, the residues of digestion still contain non- 
disengaged force. All these forces ought to be estimated if 
we want to know how much of their force in tension has been 
lost by the alimentary matters in passing through the organism, 
and how much ought consequently to be found again under 
the form of force in action. The urinary secretion also elimi- 
nates incompletely transformed products ; the urea and the 
uric acid contain force in tension, which ought to be taken 
iuto account in calculations. 

The watery vapour which saturates the air as it comes out 
of the lungs removes from the organism and cariies away with 


it a certain quantity of heat ; the same thing takes place in the 
boiler of a steam-engine, as well as in cutaneous evaporation. 

This complication in the measure of force among organized 
beings shows what difficulties await those who are en- 
deavouring to verify the principles of thermo-dj'namics in 
animals ; yet, nevertheless, it would be illogical to admit with- 
out proof that, in living beings, the physical forces do not 
obey natural laws. Several savants, firmly convinced of the 
generality of the laws of thermo -dynamics, have attempted to 
demonstrate them upon the animal organism. 

J. Beclard was the first who endeavoured to prove that in 
the muscles of man heat may be substituted for mechanical 
work, and vice versa. For this purpose he examined the 
thermo metrical temperature of two muscles, both of which 
contracted, but one worked, that is to say, raised weights, while 
the other did not work. It might have been expected that less 
heat would have been found in the first muscle, because a 
portion of the heat produced during its contraction ought to 
have been transformed into work. 

The idea which governed Beclard's experiments was 
assuredly correct, but the means at his disposal for ascer- 
taining the heating of the muscles were altogether insufficient. 
A thermometer was applied to the skin at the level of 
the. muscle, in order to give the measure of the heat pro- 
duced ; thus the variations of temperature obtained by Beclard 
according as the muscle worked or not, were so slight that no 
real value could be attached to them. 

Herdenheim obtained clearer results by operating upon 
frogs' muscles, which he made to contract with or Avithout the 
production of work, ascertaining their temperature by means 
of thermo-electric apparatus. 

Him was bolder in his experiments, for he sought to deter- 
mine the equivalent of mechanical work in animated motors. 

In order to make Hirn's experiment comprehensible, let us 
consider the simpler case of a mechanician desiring to establish 
the thermal equivalent of the work of a steam engine, knowing 
how much fuel it has burned, what heat has been given out, 
and what quantity of work has been produced. 

First, he will estimate the heat which should correspond 


with the combustion of the coal which he has burned ; he will 
prove that the heat which he has obtained is less than this, 
which is made evident by the disappearance of a certain 
number of units ; this disappearance he will attribute to the 
transformation of heat into work. Now as he knows the 
number of kilogrammetres produced by the machine, he will 
only have to divide this number by that of the units of heat 
which, have disappeared, in order to fiud the number of 
kilogrammetres equivalent to each of them. 

Him believed that the combustion effected, the heat given 
out, and the mechanical work produced by a man could be 
estimated at the same time. He enclosed the subject in a 
hermetically closed chamber, and made him. turn a wheel 
which could, at choice, revolve with or without doing work. 

The air of the chamber being analysed, showed what 
quantity of carbonic acid had been given out ; from thence 
were deduced the combustion produced and the number of 
units of heat to which that combustion ought to have corre- 

The heat given out in the chamber was ascertained by the 
ordinary calorimetric processes ; it was, in proportion to the 
work produced, sensibly inferior to that which, ought to 
have been found according to the quantity of carbonic acid 

This disappearance of a certain number of units of heat 
was explained by their transformation into mechanical work. 

From these experiments Him deduced a valuation of the 
mechanical equivalent of heat for animated motors ; but the 
number which lie obtained differed considerably from that 
\vhirh lias been established by physicists. This difference is in 
no wise surprising when we think of all the causes of error 
which are united in such an experiment. There may have been 
an error concerning the quantity of carbonic acid exhaled ; an 
error concerning the nature of the chemieal actions which 
disengaged this carbonic acid, and therefore respecting the 
quantity of heat which ought to have accompanied the disen- 
gagement; an error in the estimation of the heat dill'iisi d 
through the calorimetric chamber; iinally, an error as to the 
quantity of mechanical work produced by the subject, lu 


fact, while it is relatively easy to estimate the work of our 
muscles when employed in lifting a burden, there are other 
muscular actions which constitute an important sum of work 
and which we do not yet know how to value with precision ; 
we allude to the movements of the circulation, and especially 
to those produced by the breathing apparatus. 

The remarks which we have made upon the greater number 
of the physiological experiments from which it has been sought 
to establish numerical data, apply to that of Him. But 
though it cannot furnish an exact determination, this ex- 
periment at least enables us to perceive the manner in which 
the phenomena vary ; it shows that a certain quantity of heat 
always disappears from the organism when external work 
is produced. No greater precision could be obtained in the 
measure of thermo -dynamic transformation in. the greater 
number of steam-engines, and yet nobody disputes that in 
these motors heat and work are substituted for one another in 
equivalent relations. 



Origin of animal heat Lavoisier's theory The perfecting of this theory 
Estimates of the forces contained in aliments, and iu the secreted 
products Difficulty of these estimates The force yielded by ali- 
mentary substances is transformed partly into heat and partly into 
work Seat of combustion in the organism Heating of the glands 
and muscles during their functions Seat of calorification Interven- 
tion of the causes of cooling Animal temperature Automatic regu- 
lator of animal temperature. 

DURING a long period, animal heat was considered to be of 
a peculiar kind, distinct from that which is manifested in the 
inorganic kingdom ; this arose from certain conditions under 
which the living tissues become hot or cold, without its 
being easy to discover how this heat appears, or how it 
disappears. It was almost natural to admit that heat is 


connected with influences of nervous origin, when it was 
seen that certain violent emotions produce icy coldness in 
human. beings, whereas others bring into the countenance 
sudden heat. Now all these facts have found an explanation 
in which there is nothing to infringe the ordinary laws of 
physics. In order to comprehend them thoroughly we must 
pass under our review the production of heat and its dis- 
tribution throughout the various parts of the organism. 

It has long since been established that aliment is indis- 
pensable in the living being for the production of heat, as well 
as of muscular power. Inanition, at the same time that it 
reduces the strength of the animal, produces profound cold 
in it. We owe to the genius of Lavoisier the comparison 
of the living organism to a grate which burns or incessantly 
oxidizes substances taken from without, by borrowing from 
the atmosphere the oxygen requisite for these transforma- 
tions. This theory has triumphed over all the attacks which 
have been made upon it, and their only result has been the 
perfecting of its details. 

Let us reduce to its true proportions the comparison of the 
living organism with a burning grate. In both, an oxidable 
matter finds itself placed in relation with oxygen ; but while, 
in a grate, the natural gas comes in contact with the com- 
bustible previously raised to an elevated temperature, in the 
organism the gas dissolved in the blood comes in contact with 
materials which are themselves dissolved in that liquid, or 
which have deeply entered into the tissue of the organs. 
Thus, the circulation transports into every part of the 
organism the elements which are necessary to the disengage- 
ment of force. These bodies remain in contact, without acting 
one upon the other, until the moment arrives when a specific 
action brings about their combination. This oilice, analogous 
to that of the spark which kindles the- Hume, or to that of 
the cap which discharges gunpowder, belongs to the nervous 

When tin- oxidation is at an end, and the forces necessary 
to the functions have been s< t at liberty, there remain in the 
tissues certain products which have become useless, and which 
may be compared to the ashes in the grate and to the gases 


which go up the chimney. These products must be elimi-. 
nated. Again, the circulation undertakes this office ; the 
blood dissolves the carbonic acid and the 'salts which are the 
ultimate products of organic oxidation, and then carries 
them, in its perpetual course, to the eliminating organs, the 
lungs and the glands. 

So lung as it remained unsuspected that heat and mechanical 
work could be substituted for each other, an attempt was 
made to account for all the combustions which take place 
in the living organism, by estimating the quantity of heat 
discharged by an animal in a given time. Physicists and 
physiologists made great efforts to determine this illusory 
equality between the theoretical heat, which corresponded 
with the combustions which take place in the organism, and 
the quantity of heat furnished by the animal under experi- 

Just as a machine, when it is working, furnishes less heat 
to the calorimeter than would be given out by a simple grate 
consuming the same quantity of combustible matter, so the 
living being gives out less heat in proportion as it executes 
more mechanical work. We have seen, by Hirn's, experiments, 
that it is solely according to the difference which exists 
between the heat experimentally obtained and that theo- 
retically estimated, that we now endeavour to find the value 
of the equivalent of mechanical work in living beings. 

Whatever may be the varied manifestations of force in the 
organism, a certain portion of that force always appears 
under the form of heat, and this it is which gives to animals 
a higher temperature than that of the medium in which they 

May we not, by ascertaining the temperature of the different 
parts of the body of the animal, discover the points at which 
heat is formed, and define the actual seat of those com- 
bustions of which we establish only the distant results ? 

It is now demonstrated that the lungs, by which the oxygen 
of the air penetrates into the organism, are not the seat of 
combustion, because the blood which comes out of that organ 
is, in general, colder than that which has gone into it. It' 
two thermometers or thermometrical needles be introduced 


into the heart of an animal, in order to ascertain the tempe- 
rature of the blood which is returning through all the veins 
of the body into the right cavities, and that of the blood which 
is coming into the left cavities from the lungs, we find that 
the blood of the right-hand side of the heart is the warmer ; 
so that it follows that heat is principally produced along the 
course of the great circulation. 

If we would more particularly localize the origin of heat, 
we must take a special organ and investigate, in a com- 
parative manner, the temperature of the blood which comes 
to it through the arteries, and goes out of it through the 
veins. Thus it has been recognized that the muscles, in 
action, and the glands while they are secreting, are organs 
for the production of heat ; and in them the most energetic 
chemical action takes place. 

But we must not expect, when examining all the muscles or 
all the glands at the moment of their action, to find an un- 
varying elevation in the temperature of their venous blood. 
A third element enters into the problem ; it is the loss of 
heat which takes place while the blood is passing through the 
organ. Now., all portions of the body are not equally sub- 
jected to loss of heat ; the most superficial are the most 
exposed to them, while the deeper organs are sheltered 
against the causes of cold.* Under these conditions every dis- 
engagement of heat in the glands ought to be represented by 
an elevation of temperature in the venous blood. If, on the 
contrary, we lay the sublingual gland bare, in cold w r eather, 
and investigate the temperature of the blood in the veins of 
that gland, we shall find the blood colder than that which 
lias entered through the arteries. Must we conclude from 
thence that there has been no disengagement of heat in that 
gland ? In no wise. We must simply admit that the loss 
of heat has exceeded its production. 

In short, heat appears to be produced in all the organs, 
but in various degrees, according to the intensity of the 

* "Wlii-n we wish to ascertain the im n;i e "I 1 t> in] 'nature- of the hlood 
in the glands, we n.nst rlmosc, fur this investigation, the Mood of the 
veilis of the livn or the ki<lm\>, mpm.s .slidtrivd IVum OM,lm- inlluuiici-s. 


chemical action which takes place in them. The temperature 
of an organ necessarily results from the heat supplied to it 
by the blood, from that which has been produced in its 
interior, and from that which it has lost. Thus it is that 
certain veins, those of the limbs, for example, bring back 
blood colder than that of the corresponding arteries ; whilst 
others, like the sub-hepatic veins which leave the liver, bring 
back blood warmer than that which has entered the hepatic 
gland. In fact, after all compensations are made, the heated 
venous blood predominates in the living organism, over the 
cooled blood ; so that it re-enters the heart 1 1 warmer than 
when it came out of it. 

This leads us to study the question of the temperature of 

Among the different animal species, some, while producing 
heat, are subject to the variations of the surrounding tem- 
perature, so that they have been called cold blooded. They are 
now called animals of variable temperature, which is more 
exact. As for the animals called warm blooded, they possess 
the singular property of having the blood in the deeper 
portions of their bodies almost always at the same tempera- 
ture, notwithstanding the variations of the external heat. 
Thus, a man, sailing from the polar regions to the equator, 
may be subject, in a few weeks, to changes of 30 in the 
surrounding temperature, but his blood remains at about 

It is easy to understand that in the midst of incessant 
variations in the production of heat inside the organism, 
and of the no less great variations in the causes of its 
waste, such uniformity can only be obtained by means of a 
regulator of the temperature. We shall now proceed to certain 
developments of the wonderful functions of the regulator of 
the animal temperature. 

Human industry has often found it difficult to provide fixed 
temperatures, or at least to counterbalance the causes of ex- 
cessive heat and cold. A hot -house must neither fall below, 
nor rise above a certain temperature. But this problem is 
relatively a simple one ; the hot-house is always warmer 
than the external air ; it can only be subjected to more or less 


intense causes of cooling, which may lie compensated by a 
suitable variation of heat. Bunseii's regulator solves this 
problem satisfactorily, by regulating the supply of gas which 
serves as a combustible, augmenting it if the inclosed air 
tends to grow cold, diminishing it in the opposite case. 

In the animal economy, two orders of influences tend in- 
cessantly to cause variation of temperature in its production 
and in its expenditure. Causes of loss of temperature exist, 
as in the instance just mentioned. The temperature of the 
surrounding air, against which our clothing protects us more 
or less efficiently, on the one hand, and the more or less 
easy evaporation by means of cutaneous perspiration, accord- 
ing to the hygrometrical state of the atmosphere on the 
other ; the action of the wind, or of air-currents ; the tem- 
perature of the baths which we take, all these different 
causes tend to increase or diminish the waste of heat to 
which the body is subject. To these influences must be added 
those of the hot or cold food which we eat ; of the hot or 
cold air introduced into our lungs by respiration, &c. All 
these constitute in general the causes of loss of heat. 

Auother variable element in the establishment of the 
animal temperature is the production of heat which takes 
place in the interior of the organism, and which, as well as 
its loss, varies under numerous influences. The aliments of 
which we partake, act, through their nature and quantity, on 
this production of internal heat ; the activity of the glands 
causes a discharge of caloric ; and the case is the same with 
respect to muscular action, which cannot be produced without 
the heating of the muscle. 

It is true that within certain limits our senses warn us to 
restrict the production of heat, or to promote it, according as 
external influences diminish or augment its waste. Thus, 
the amount of food taken varies "with climate, so that the en- 
force! sobriety of the dweller in hot countries has no raison 
d'etre in cold ones. Obligatory idleness during the heat 
of the day under a burning sky is one manner of diminishing 
the production of heat; the Northmen, on the contrary, en- 
deavour to compensate, by muscular activity, for tho cold to 
\\ hich they are subjected. 


But these are not the true regulators of the animal 
temperature. Our will commands all those actions whose 
influence may be favourable to the regulation of our tempe- 
rature ; but, in general, Nature, in order to secure the indis- 
pensable functions of life, removes them from the control of 
our will. It is in an automatic apparatus that we shall find 
the real regulator of temperature. 

This apparatus must obey external and internal influences 
at the same time, it must retain heat when it tends to be 
dissipated too rapidly, and, on the other hand, it must facili- 
tate its decrease when it is produced too abundantly within 
the organism. 

This double end is achieved by a property of the circu- 
latory system : the blood vessels, animated by nerves whose 
action has beea revealed by M. Cl. Bernard, close under the 
influence of cold, and open under the effect of heat. This 
property regulates the course of the blood in each of the 
organs, and at the same time the temperature throughout the 
entire economy. 

Let us take an animal which has just been killed; the 
circulation of the blood is stopped, and with it all the 
functions. This animal, if placed in a low temperature, 
becomes cold. According' to physical laws, the extremities of 
the limbs and the surface of the body will lose heat in. the 
first instance, while the central portions will still remain very 
hot, being sheltered by the more superficial layers against the 
causes of loss of heat. This corpse will resemble an inert 
body which has been heated, and is growing cold. The cir- 
culation of the blood opposes itself, during life, to the 
unequal partition of heat over the various poiuts of the 
organism ; bringing the arterial blood, at a temperature 
of nearly 38 (centigrade), to the superficial portions, it warms 
them when the external temperature tends to chill them. On 
the other hand, if, in the living animal, the production of 
heat has been augmented, the circulation opposes the inde- 
finite heating of the central regions of the body ; it brings 
that heat to the surface, where it is lost in contact with the 
external colder medium. 

The effect of the circulation of the blood is therefore to 


render the temperature of the organism uniform. But this 
uniformity is never complete; in fact, except in the case of the 
animal's being in a vapour bath at 38, and losing none of 
its heat, the surface of the body is always colder than the 
interior, but no ill effect is produced by the chill, which does 
not act upon the essential organs. 

If the circulation of the blood were of equal swiftness in every 
part, such a uniformity would not result in the preservation of 
the uniform temperature necessary for the internal regions of 
the body; we should then merely see it exposed to more general 
elevations and depressions of temperature, according to the re- 
spective predominance of causes of heat or the loss of it. To 
produce uniformity of central heat it is indispensable that some 
influence should augment the rapidity of the circulation 
each time that the organism produces more heat, or that the 
elevation of the surroundiug temperature diminishes the causes 
of cooling. Circulation in the superficial portions of the body 
is extremely variable, as we may ascertain by observing the 
varying aspects of those portions, which are sometimes red. 
hot, and swollen, sometimes pale, cold, and shrunken, accord- 
ing to the more or less abundance of the blood which circu- 
lates in them. This variability depends upon the contraction 
or the relaxation of the little arteries, whose muscular sheaths 
obey special nerves. When, under the influence of these nerves, 
named vaso-motors, the vessels contract, circulation slackens, 
while by a contrary action, the relaxation of the vessels ac- 
celerates the course of the blood. Now, it is the tempera- 
ture itself "which most generally acts in regulating this state 
of contraction or relaxation of the vessels, so that the animal 
temperature possesses in reality an autmiuitif regulator. 

Every one has observed the influence of heat and cold on 
the circulation in the skin. If we dip one hand in hot, and 
the other in cold water, the first will grow red and the second 
pale; heat has, therefore, the effect of relaxing, and cold of 
contracting the vessels. In other words, according to what we 
have already seen, heat, by its action upon the circulation, 
favours the loss of heat ; while cold acts in an inverse sense, 
and tends to diminish the intensity of tin: chilling process. 
And it is not only under the influence of the variations of the 


external temperature that these effects are produced ; they are 
equally observed when the animal heat varies in its produc- 
tion. The heating 1 of the organism which accompanies 
muscular activity, or which results from taking very hot 
drinks, produces the acceleration in the superficial circulation, 
which throws out this excess of heat to the surface. Inanition, 
muscular repose, the drinking of iced waters, &c., slacken the 
circulation near the surface and check its cooling action. 

Such are, as far as we can explain them in a short chapter, 
the origin and the distribution of heat in the animal organism. 
The part played by the circulation of the blood in the distri- 
bution of heat, perhaps demands more ample details ; and, 
indeed, we have treated it more fully elsewhere.* In the 
present chapter we have studied heat only as manifestation of 
force, and have merely designed to show that, notwithstanding 
all appearances, heat is of the same nature in the inorganic 
world and in organised beings. 



Motion is the most apparent characteristic of life ; it acts on solids, 
liquids, and gases Distinction between the motions of organic and 
animal life We shall treat of animal motion only Structure of the 
muscles Undulating appearance of the still living fibre Muscular 
wave Concussion and myography Multiplicity of acts of contrac- 
tion Intensity of contraction in its relations to the frequency of 
muscular shocks Characteristics of fibre at dillerent points of the 

MOTION is the most apparent of the characteristics of life ; 
it manifests itself in all the functions ; it is even the essence of 
several of them. It would occupy much space to explain the 

* Physiologic medicalc de la. Circulation die Sang. Paris, 18G3 ; and 
Theorie physiologique dit ClwUra, Gazette Hcbdomadaire de Medecine. 


mechanism by which the blood circulates in the vessels, how 
air penetrates into the lungs, and escapes from them alter- 
nately, how the intestines and the glands are perpetually 
affected by slow and prolonged contractions. All these move- 
ments take place within the organs without the exercise of the 
will ; frequently even the individual in whom they occur is 
unconscious of them ; these are the acts of organic life. 

Other movements are subjected to our will, which regulates 
their speed, energy, and duration; these are the muscular 
actions of locomotion, and the different acts of the life of rela- 
tion. We shall treat specially of this order of phenomena, 
which are more easy to observe, and to analyse. Suffice it 
here to say that the absolute division between the acts of 
organic life and those of the life of relation ought not to be 
accepted unreservedly. Bichat, who established it, based it 
upon anatomical and functional differences which are of less 
importance now than they were in his time. The mus- 
cular element of organic life is unstriped fibre obedient to the 
nerves of a particular system called the great sympathetic, 
on which the will has no action ; motions produced by this 
kind of fibre are manifested some time after the excitement of 
the nerve or of the muscle, and continue for a considerable 
time. In fact, the object of those acts which are intended to 
maintain the life of the individual imprints upon them a 
special character. The muscular element of the life of rela- 
tion consists of a fibre of striated appearance, whose action, 
under the control of the will, is dependent upon nerves 
emanating directly from the brain or from the spinal marrow. 
These movements become evident rapidly as soon as they are 
provoked by excitement; they are of brief duration, and are, 
generally, not indispensable to the maintenance of the life of 
the animal. 

Although this distinction is, in a general way exact, it is 
plain that it is too arbitrary, and that numerous except ions 
to the anatomical and physiological laws which it tends to 
establish may be quoted. Thus, the heart, an organ directly 
indispensable to organic life, and not under the governance of 
the will, is a structure which much resembles the voluntary 
muscles. Certain fishes of the genus tinea have striated muscles 


in the large intestine, as Ed. Weber lias pointed out. Very 
often, on the other hand, the will has no power over certain 
muscles which, by their structure, and by the nature of the 
nerves which animate them, belong to the system of the life 
of relation. Habit, besides, by repeated exercise, appears to 
extend the action of the will over the muscles, almost 
indefinitely. The young animal shows, by the awkwardness 
of his movements, that he is not in full possession of his 
muscular functions; he seems to have to study the simplest 
acts, and performs them badly ; while the gymnast, or the 
skilled piano forte-player executes prodigies of agility, strength, 
or precision, without any apparent effort of the will propor- 
tionate to the result obtained. Many physiologists think, and 
we are of the same opinion, that there exist in the brain, 
and in the spinal marrow, centres of nervous action which 
acquire certain powers, by force of habit. They attain to the 
command and co-ordinal ion of certain groups of movements 
without the complete participation of that portion of the brain 
which presides over reasoning and the consciousness of our 

Let us lay aside these questions, which are still under inves- 
tigation, and examine into the production of motion in a 
voluntary muscle. The organ which generates motion is 
composed of several elements. Simple as it is supposed to 
be, it requires the intervention of muscular fibre, of the blood 
vessels, which unceasingly convey to it the chemical elements 
at whose expense the motion is to be produced, and finally, of 
the nerve which excites motion in the fibre. 

When the physiologist desires to analyse the actions 
which take place in the muscles, he does not deal, in the first 
place, with voluntary motions, whose complexity is too great. 
The operator isolates a muscle, and induces motion in it, by 
bringing to act upon its nerve artificial excitements which he 
has under his control. 

To give an idea of the part played by each of the elements 
of the motive apparatus in the production of movemeit", it is 
sufficient to operate upon the leg of a frog. By laying bare 
and severing the sciatic nerve, the influence of will upon the 
muscle may be suppressed, so that the latter will only execute 


such motions as are produced by excitation, electric or 
otherwise, applied to the portion of the nerve which remains 
in communication with it. Ou the sides of the sciatic nerve 
are an artery and a vein. Compression of the artery will 
prevent the blood from reaching the muscle ; compression of 
the vein will produce stagnation of the blood. The influences- 
which different states of circulation produce upon the muscular 
function may then be observed ; and, finally, by making an 
incision in the skin of the foot, the muscle will be laid bare, 
and cold, heat, or the various poisonous substances by which 
its action is modified, may be brought to bear directly upon it. 

When the nerve of a frog thus prepared is excited by an 
electric discharge, a very brief convulsive movement in the 
muscle is produced; this motion is called Zuckung by the 
German physiologists, and we propose to call it shock, in 
order to distinguish it from true contraction. It is so rapid 
that its phases cannot be distinguished by the eye, so that, to 
appreciate its characteristics aright, recourse must be had to 
special instruments. Registering apparatus only can supply 
this need, for they faithfully render all the phases of motion 
communicated to them. The general disposition of these forms 
of apparatus, which for a long time were used almost exclusively 
in the service of meteorology, is generally known. The 
indications of the barometer, of the thermometer, of the force 
or the direction of the wind, of the quantity of rainfall, &c. , 
register themselves under the form of a curve which, accord- 
ing as it is elevated or depressed, expresses the increase or 
diminution of intensity of the phenomenon to be registered. 
The time during which these variations are accomplished may 
be estimated by the length occupied by the curve upon the 
paper, which travels in front of the marking pen with an 
ascertained and perfectly regular speed. 

The use of instruments of the same kind has been introduced 
into physiology by Volkmann, Ludwig, and Ilelmholtz. We 
have endeavoured to extend the employment of them to a great 
number of phenomena, and we have constructed many instru- 
ments whose d( si'.ription would be out of place here. The 
apparatus which registers muscular motions bears the name 
of myograph , it shows the disturbance of the muscle by 



means of a curve T\ hich readily allows us to study its phases. 
We have fully explained elsewhere the nature of this in- 
strument, the experiments for which it is suitable, and 
the results which it gives.* At present we shall limit our- 
selves to a summary description of the chief results of 

FIG. 2. The Myograph. 

In order to explain thoroughly the function of the appa- 
ratus, let us reduce it in the first place to its essential 
elements. Fig. 2 shows a muscle of the calf of a frog's leg, m, 
suspended by a clip by means of the bone to which the upper 
part of the muscle is attached. The tendon, t, of the muscle 
has been cut and then tied by a thread to the lever, L, one end 
of which can be raised or lowered while the other is fixed ; the 
nerve, n, is susceptible of electric excitement, which produces 
certain contractions followed by relaxations in the muscle, that 
is to say shocks. Eacli of these movements of the muscle is 
communicated to the lever, which is raised or lowered, ampli- 

* Du Mouvcment dans Ics Functions dc la Vie. Paris, 1S67 : G. Bailliere. 


fying at its extremity the motions which it has received. 
This lever, which ends in a point, traces on a turning cylinder 
certain curves, which, when they are raised, indicate the con- 
traction of the muscle, and when they are lowered, show 
its return to its primitive length. 

With the arrangement which we have made in the myograph 
a muscle may be operated upon without being detached from 
the animal, which allows of the organ being left in the normal 
conditions of its function. 

In Fig. 3 the frog is represented in the experiment, fixed, 
by means of pins, on a piece of cork. 

Fi<:. :;. M.uvy's 

The brain and spinal marrow have been previously destroyed, 
so as to extinguish all voluntary movement and sensibility. 
Although, to all appearance, the animal is dead, it will never- 


theless retain for several hours the circulation of the blood, 
and the power of motion under the influence of electric 
discharges. An electric excitator conveys the current from an 
induction coil to the nerve of the frog. 

In order to register these movements and to depict them 
by curves which express tlu-ir different phases, they are trans- 
mitted to the myograph in the manner already described. 
The tendon of the muscle is cut, and connected by a wire 
which is fastened at the other end to the lever of the 
registering apparatus ; the latter moves in a horizontal plane, 
when the contractile force of the muscle is exerted upon it. 
As soon as the muscle ceases to act, the lever returns, under 
the pressure of a spring, to its original position. At the free 
extremity of the lever is a point which traces, on a turning 
cylinder covered with smoked paper, the motions produced by 
the alternate contraction and relaxation of the muscle. 

When the cylinder is motionless, the lever traces, for each 
muscular shock, a straight line which expi'esses (l>y amplifying 
it in a known proportion) the extent of the contraction of the 
muscle. Several authors limit themselves to this kind of 
myography, by which they ascertain the variations produced by 
different influences in the intensity of muscular action. By 
giving the cylinder a rapid rotiitory motion, a curve is obtained 
\\hich expresses by its height the extent of the contraction, 
and indicates by its inclination, which constantly varies, the 
speed with which the muscle passes through the different 
phases of the shock. Finally, in order to obtain, without 
confounding them, a great number of successive tracings, 
the foot of the myograph is placed upon a little railroad 
which works parallel to the axis of the cylinder. Tha 
writing point then traces an indefinite spiral all round the 
cylinder, and on this spiral a number of regularly graduated 
curves (Fig. 5) are traced, answering to a series of electric 
excitations produced at equal intervals ; each of these curves 
corresponds with one of the electric shocks. 

If the speed with which the cylinder turns be augmented 

or diminished, a change ensues iu the appearance of the 

curves, which necessarily occupy a greater or less space on 

the paper, but if a uniform speed in the rotation of the 



cylinder be maintained, the curves retain the same form so 
long as the muscle gives the same movements. 

Not only are shocks produced iu the muscle by acting 
upon its nerve by electricity, but also by applying electric 
excitement to the muscle itself. Pinching, percussion, and 
cauterization of the nerve are also excitants which provoke 
shocks of the muscle. 

The character of these movements changes under certain in- 
fluences. Fatigue of the muscle, the cooling of that organ, the 
stoppage of circulation in its interior, modify the form of the 
shock, diminish its force, and augment its duration. Under 
these influences the myographic curve passes through different 
forms, such as 1, 2, 3, Fig. 4. 

Fir.. 4. Character of the shnck, according to the dearree of fttjgiie of the 
muscle : 1, muscle fresh ; ~2, muscle a httlu fatigued; 3, musclo still mure 

Among the different species of animals, the durations of the 
shock vary considerably ; in the bird they are very brief (two 
to three hundredth?) of a second). In man they are longer ; 
in- the tortoise and hyberuating animals longer still. Certain 
poisons modify the characteristics of this movement in so 
special a manner, that the slightest traces of those poisons 
introduced into the circulation of the animal may be disco- 
vered in the form of the tracings. 

By Fig. 5, we may judge of the successive forms which 
will be assumed by the shocks of the muscle of a frog, under 
the influence of a gradual absorption of vcratrine. 

These experiments still reveal only one fact: it is that 
the muscle is shortened or lengthened by a movement whose 



phases vary under the different influences which we have just 

If we endeavour to pursue the study of this phenomenon of 
the contraction of the muscle, we see that it is only a change 
in the form of that organ, arid that the diminution of length 
is accompanied by a corresponding dilatation which might 
be expected in a sensibly incompressible tissue. But the 
manner in which this dilatation is produced is curious. 

Fio. 5. Successive transformations of the shock of a muscle becoming poisoned by veratrine. Underneath to the left of the fi^me 
are shown the first effects of the poison. 

It has been long since observed that there are formed upon 
living muscles at the points where they are excited, lumps or 
nodosities which run along the whole length of the muscle, 
with more or less rapidity, like a wave on the surface of the 
water. Aeby* has shown that this is a normal phenomenon, 
and, under the name of muscular wave, he has described this 
movement, which, from the excited point, passes to the two 
extremities of the muscle at the rate of about a metre in a 
second. By means of an apparatus, which we have called 

* Unterwiehnngen ubcr die Fortpflanzungsgeschioindi ikcit dcr Rcizungs in 
der querzge^treiften Muski'lfascrn. Braunschweig : 1862. 


clips, the reality of this movement of the wave 
may he verified in. the living animal. 

When the wave appears in the muscle, it produces con- 
traction. During the whole of its passage the contraction 
continues, and when, having reached the end of the muscular 
fibre, the wave vanishes, the contraction disappears with it. 

These facts resemble those which the microscope reveals in 
living muscular fibre. Let a bundle of muscular fibres be 
taken from an insect, and placed under the objective of the 
microscope (the feet of coleoptera are well suited for this 
purpose) ; we first observe the beautiful transverse striation 
of these fibres, and then we perceive on their surface an uudu- 
latory movement often alternating, which resembles the motion 
of waves on the surface of water. Ou examining this 
phenomenon more closely, we see that the transverse striio 
of the fibre are, at certain points, very close together, which 
is shown in the figure by a dilatation of the fibre. This 
is the wave shown by the microscope ; the longitudinal con- 
densation of the muscle at this point gives it greater opacity 
than in the other portions (Fig. 0.) This opaque wave travels 

|.' K; c. Appearance prc'sentcd by a wave in muscular fibre. 

through the length of the fibre. In other words, the points 
at which the stria> approach each other are not always the 
same, the longitudinal condensation disappears in one place 
whilst it is produced in the contiguous parts. 

Since the contraction of the muscle is accompanied by its 
transverse dilatation, we may study the characteristics of 
the motion produced in a muscle, according to this expansion. 

We have sncr l'-d in registering these changes in the 

volume of the muscle, as we have registered the changes 
in its length. Under these conditions we might study 
muscular action in man himself, because there is no need 
of mutilation. 

Let us suppose a muscle held between the flattened ends of 



a clip ; at eacli of its dilatations the muscle will force open 
the clip, and this movement may be registered. This method 
enables us to study the phenomenon of the muscular wave, 
and the speed with which it travels throughout the whole 
length of the muscle. 

Fig. 7 exhibits a bundle of muscle held at two points 
of its length between the myographical clips, 1 and 2. 
Those instruments are so constructed that when their ends 
are pushed apart by the dilatation of the muscle, the move- 

G. 7. Disposition of a bundle of muscle between two pairs of myo- 
graphical clips. Clip No. 1 holds the electric excitators of the mnscl'-. A 
wave is represented at the moment when it has just crossed each ot the 

ment compresses a sort of little drum which sends a portion 
of the air which it contained through an india-rubber tube 
into a similar little drum. Fig 1 . 7 shows two of these instru- 
ments fixed upon a foot. The expansion of the membrane 
lifts a registering lever, and thus gives notice of the dilatation 
of the muscle at the point where it is compressed by clip 
No. 1. The movement is shown upon the tracing- by a curve 
analogous to those which we have already seen. 


Let us suppose that the muscle is electrically excited at 
tlie level of the first clip ; notice is given of the formation of 
the uave at that part of the muscle, but clip No. 2 does 
not yet give its signal. In order that it may act, the wave, 
as it passes along the muscle, must reach it. As this occurs, 
clip No. 2 gives the signal in its turn, and it is shown by 
the tracing, that this second movement is later than the first 
by a certain space whose duration maybe estimated according 
to the speed of the rotation of the cylinder. 

The influences which modify the intensity and the duration 
of the muscular shock have appeared to us to modify the 
intensity and the speed of the propagation of the wave. Thus 
the two lower curves represented in Fig. 8 show that the 
transference of the wave is retarded by cold. 

Fio. 8. Two determinations of the speed of the muscular wave. 

The experiment has been made upon the muscles of the 
thigh of a rabbit. The clips were placed as far as pos- 
sible apart, about seven centimetres. Electricity was applied 
to tin' linn'f I'.i'tinnitu of the muscle, and the two upper curves 
of Fig. 8 were obtained. The interval which divides those 
curves marks the duration of the transference of the muscular 
wave. Aft'.-r the muscle had been chilled with ice the curves 
at the, bottom of the figure were obtained. We see that the 
tra:isfeivnc3 of the wave is slackened, for there is a longer 
interval between the*e curves than between the first. 

Pfi>iliii'ti<ni <>f iiii'cliiuiii-iil J'nnr in the iiniscl<>. We have seen 
that chemical action is the source of muscular foive ; through 



what modi. i does this force pass before it becomes mechanical 

work ? 

In steam engines, heat is the necessary medium between 

the oxidation of the fuel and the developed mechanical work. 

It is ver} 7 probable that the same 

thing takes place in the muscles. 

The chemical action produced by 

the nerve within the fibre of the 

muscle disengages heat from it : 

this heat in its turn is itself 

partially transf trnu'd into work. 

We say partially, since accord- 
ing to the second principle of 

tliermo-dynamics, heat cannot be 

entirely transformed into me- 
chanical work. 

Certain facts seem to justify 

these views : thus, by warming 

a muscle, we change the form of 

it, and may see it contract in 

length as it expands in breadth. 

These effects disappear when the 

muscle is cooled. 

Muscular fibre is not singular 

in its power of transforming heat 

into work. India-rubber, for in- 
stance, has an analogous property, 

and this substance may be made 

to imitate the muscular phe- 
nomena to a certain degree. If 

we take a strip of india-rubber 

(not vulcanised), and, drawing it 

between the fingers, stretch it out 

to ten or fifteen times its original 

length, we see that it becomes 

white, and of a pearly lustre. 

will become sensibly warm, and it will tend energetically to 

return to its original condition, so that if we let go either of 

its ends, it will instantly resume its former length, and fall to 

Put. (. Transformation of heat into 
work by a strip of iiid.a rubber. 

At the same time the strip 


its original temperature. According to our view, the sensible 
heat lias disappeared and become mechanical work. If we 
plunge the strip \vhen extended into water, so as to deprive it 
of its heat, it. remains, as it were, congealed iu its extended 
state, and does not develop any mechanical work. But if we 
restore to the elongated strip the heat which it had lost, it 
will recover its elasticity with considerable force. Fig. 9 
represents a strip of india-rubber thus pulled out and co< led. 
It has been laden with a weight that it may have no tendency 
to recover itself. But, if we take the strip between our fingers, 
we feel it swell and shorten at the same time that it lifts the 
weight ; there is again production of mechanical work. 

If we thus heat the strip at various points we create a 
series of lateral expansions, each of which raises a certain 
quantity of the weight. Lastly, if we heat it throughout all 
its extent, the strip returns to its original dimensions, with 
the exception of the slight elongation produced by the sus- 
pended weight. 

Strong analogies exist between these phenomena, and 
those which take place in muscular tissue. The identity would 
be perfect if the wave which heat produces on the strip of 
india-rubber were transmitted to each end. This transference 
implies, in the muscular fibre, the successive propagation 
of the chemical action which disengages the heat. It is thus 
that if we light a train of powder at one point, the in- 
candescence spreads throughout its entire length. 

These analogies have struck us as being remarkable : thov 

f-s v 

seem to us to open, new views of the origin of muscular 




The function of the nerve Rapidity of the nervous agent Measures of time 
iu physiology Tetanus and muscular contraction Theory of con- 
traction Work of the muscles. 

THE experiments described in the preceding chapter show 
us the muscle under artificial conditions, which may, perhaps, 
induce us to suspect the results which they furnish. Cau 
this electrical agent, which has been employed to excite 
motion, be assimilated to the unknown agent which the will 
sends through the nerves to command the muscles to act ? 
And these artificially-produced movements, those brief shocks, 
always similar if the conditions of the muscle be not changed, 
in what do they resemble the motions commanded by the 
will, which are so varied in their form and their duration ? 
These objections deserve at least a brief discussion. 

The function of the nerve. When a nerve is excited by an 
electric discharge, the electricity employed does not always 
pass to the muscle in which the reaction takes place. The 
shock is produced equally well when all propagation of the 
electric current along the nerve is prevented, and it exhibits 
itself equally when excitants of a quite different nature are 
employed, for instance, pinching or percussion. Thus, the 
excitant employed only excites in the nerve the transference 
of the agent which is proper to that organ. Is not this 
nervous agent itself electricity? Notwithstanding the able 
labours of the German physiologists, and especially of 
M. I)u Bois Reymoud, science has not yet decided on that 
subject. We know that electric phenomena are produced in 
the nerve when it has been excited in a certain way, and 
that their propagation throughout the nervous cord seems 
to have precisely the same speed as that of the transference 
of the nervous energy itself. How has this speed been 
measured ? 


Ilolmlioltz had tlie boldness to undertake tliis measurement, 
and, by determining 1 the speed of the nervous agent, lie has 
furnished physiologists with a method which enables them to 
measure the duration of other phenomena connected with the 
nervous or muscular functions. Thus the experiment described 
above, in which we have measured the speed of the trans- 
ference of the wave in a muscle, is only an application of the 
method of Ilelmholtz. 

In order to make tli9 conditions of this experiment 
thoroughly comprehensible, let us make use of a comparison. 
Let us suppose that a letter is despatched from Paris to go to 
Marseilles, and that, being resident in the latter town, we 
should be informed of the precise instant at which the postal 
train leaves Paris, while we have nothing- to warn us of its 
arrival at Marseilles except the knowledge of the moment at 
which the letter is delivered there. How can we, according to 
these data, estimate the speed of the mail train ? It is clear 
that the instant at which we receive the letter does not indi- 
cate that of the arrival of the train ; fur between that arrival 
and the distribution, many preliminaries take place, the sorting 
of letters, delivery, &c., which require a certain time not 
within our knowledge. In order to have an exact idea of the 
speed of the train which carries the mail, we must receive 
a signal of the passage of that train through an intermediate 
station between Paris and Marseilles, Dijon, for instaiice ; 
then we shall see that the distribution of letters takes place 
fdx hours sooner after the departure from D jon than after tho 
departure from Paris. Knowing (he distance which separates 
these two stations, we may ascertain from the time employed 
in traversing it, the speed of the train. By supposing this 
speed to be uniform, we shall know the hour at which the 
train will have arrived at Marseilles, which will give us know- 
ledge of the time consumed in the sorting and distribution of 
the letters. 

Ilelmholtz, in experimenting upon the nervous motive 
agent, first excited the nerve at a point very distant from the 
muscle, and noted the time which elapsed between the excite- 
ment which despatched the message carried by the nerve, and 
the appearance of motion in the muscle. Then acting on a 


point of the nerve very near to Ilie muscle, lie ascertained 
that tinder these new conditions Ilie motion followed the ex- 
citement more closely. The diffeience of time which he 
observed in these two consecutive experiments measured the 
duration of the transference of the nervous agent along the 
known length of the nerve, and consequently expressed its 
speed, which varied from 15 to 30 metres per second. It 
is feebler in the frog than iu warm-blooded animals. 

FIG. 10. --Determination of the speed of the nervous agent in man. 1. Shock 
produced when the nerve has been excited vi ry close to the muscle. 
2. Shock produced by the excitement of the nerve at a farther distai ce 
of 30 centimetres. D, Vib atinn of a chronographic tuning-fork vibrating 
250 time* in a second, to measure the time which corresponds with 
the iuterval of the shocks. 

Now, it results from the experiments of Helm holt z, that all 
the time which elapses between the excitement and the motion 
is not occupied by the transference of the nervous agent ; but 
that the nuiscle, when it has received the order carried by the 
nerve, remains an instant before acting. This is what Helm- 
holtz calls lost time. This time would correspoud, in the 
comparison which we have employed above, with the duration 
of the preparatory labour between the arrival of the letters 
and their distribution. 

Physiologists have repeated the experiment of Helmholtz 
with some improvements. In fig. 10 tracings may be seen 
which we have oxirselves obtained while measuring the speed 
of the nervous agent. 

Two muscular shocks are successively registered upon the 
same cylinder, care being taken that the nerve shall be excited 
in the two experiments, at different points, but at the same 
instant with regard to the rotation of the cylinder; for 
example, at the precise moment at which the point of the 


myograpli passes over the vertical which corresponds with the 
origin of the lines 1 and 2. 

In the experiment which regulated the shock of line 1, the 
nerve was excited very near the muscle. In that which was 
traced by the shock of line 2, the nerve was excited 30 centi- 
metres farther off. As the cylinder turns with a uniform 
motion we can estimate the time corresponding with the 
distance which separates the two shocks. To facilitate the 
measurement of this interval, the vertical lines indicate the 
starting points of these shocks; in fig. 10 the interval which 
separates them corresponds with a hundredth of a second, 
during which the nervous agent has passed over 30 centi- 
metres of nerve, which corresponds with a speed of 30 metres 
per second. In order to measure this time with very great 
exactitude, we use a method invented by Duliamel. It con- 
sists in making the cylinder trace the vibrations of a chrono- 
graphic tuning-fork provided for this purpose with a very 
fine style, which scratches on the sensitive paper. We have 
recourse to this method in all our experiments. 

Let us return to fig. 10. If the interval w r hich divides the 
starting points of the two shocks corresponds with the time 
which the nervous ngent lias taken to pass along 30 centi- 
metres of nerves, there is a much more considerable time, 
which, for each of the lines 1 and 2, is measured between the 
signal of the excitement marked by the first of the three 
vertical lines and the first shock. This is the lost time of 
Helmholtz ; it represents more than a hundredth of a second 
in this experiment. 

The greater number of authors think that the speed of tho 
nervous agent varies under certain influences ; that heat 
augments it, while cold and fatigue diminish it. 

It seems to us, on the contrary, that this variability of 
duration belongs almost exclusively to those still unknown 
phenomena which are produced in the muscle during the 
lost time of Helmholtz. 

Just as the employes o the post, fatigued or chilled by cold, 
cause delay in tin- di^trUiutiou of despatches, without there 
having been any change- in tin- speed of the train which has 
brought them, so the unix/lc-, according to whether it is rested 


or fatigued, heated or chilled, executes more or less rapidly 
the movement dictated by the nerve. 

Besides this, all the influences which cause variation in the 
moment at which the shock of the muscle appears, cause 
variation of speed in the propagation of the wave in its 
interior ; which proves that the conditions which accelerate 
or retard chemical actions, the first causes of all these phe- 
nomena, are solely concerned. 

Of the contraction oj the muscle. Hitherto, we have applied 
to the nerve only one single excitation, to which one single 
motion responded, the muscular shock. Notwithstanding its 
brevity, this shock has an appreciable duration ; in man it takes 
8 or 10 hundredths of a second for the muscle to accomplish 
its contraction ; then a longer time for it to resume its normal 
length ; after which, if it receives a new order from a nerve, 
it gives a fresh shock. But if the excitations of the nerve 
succeed each other at such short intervals that the muscle has 
not time to accomplish the first shock before it receives a 
second, a special phenomenon is produced ; these movements 
are confounded and absorbed into a state of permanent con- 
traction, which lasts as long as the excitations go on suc- 
ceeding each other at short intervals. 

Thus the shock is only the elementary act in the function of 
the muscle ; it plays therein, after a fashion, the same part as 
a sonorous vibration plays in the complex phenomenon which 
constitutes sound. When the will ordains a muscular con- 
traction, the nerve excites in the muscle a series of shocks 
which follow one another so closely that the first has not time 
to end before a second begins, so that these elementary 
movements combine together and coalesce to produce the 

Volta pointed out, in a letter to Aldini, this singular fact, 
that a frog which receives a series of excitations, by the reite- 
rated contacts of two heterogeneous metals applied to his 
nerve, does not react at each of these contacts, but undergoes 
a sort of permanent contraction. Ed. Weber shows that the 
action of successive induced currents is of the same kind, 
and he has given the name of tetanus to the state of the 
muscle thus excited. Helmholtz perceived that the muscle 


vibrates in the depths of its tissue under these conditions of 
contraction, because the ear applied to this muscle hears a 
sound whose acuteness is ex ictly determined by the number 
of the electric excitations sent to the muscle in a second. 

Uy means of a very sensitive myograph, we have been able 
to rentier visible the vibrations of the muscles under the in- 
liuence of tetanus -producing shocks. 

Fig. 1 1 shows how this fusion of shocks is manifested 
by a contraction of the muscle, permanent, in appearance, but 
in which the tracing reveals vestiges of vibration*. Vibrations 
may be found in the tetanus which strychnine produces in the 
muscles of an animal, as well as in that which is caused by 
the irritation of a nerve by heat and chemical agents. 

FIG 11. Gradual coalescence of the shocks produced by cle. trie excitations of 

iuae.ising frequency. 

In short, these voluntary contractions seem to be only a 
series of shocks, combining together by the rapidity of their 

It has long been known that by applying the ear to a 
muscle in a state of voluntary contraction, we can hear a 
grave sound, whose tone several authors have sought to 
determine. "Wollaston, Iloughton, and Dr. Collongue are 
almost agreed upon this tone, which would correspond to a 
frequency of ',','2 or .">"> vibrations per second. Helmholtz 
thinks that this tone of ;'>'_' vibrations per second is the normal 
sound given out by the muscle in contraction, and according 
to liis i .xperimeuts in electric totalization, he regards this 


number as the minimum necessary to produce tlie state of 
apparent immobility of the electrically tetanized muscle. 

If voluntary contraction, studied with the aid of the myo- 
grapli, furnishes no trace of vibrations, Ave must not be sur- 
prised, since the essential character of that act consists in the 
coalescence of shocks. But the existence of the sound which 
accompanies the contraction of the muscle sufficiently proves 
the complexity of this phenomenon. Let us add another proof 
in favour of this theory. "When a muscle receives excitations 
of equal intensity, the contraction which results from them is 
all the stronger in proportion to their frequency. Now, in 
contracting the muscles of the jaws with more or less force, 
we have been able to convince ourselves that the acuteness of 
the muscular sound increased with the energy of the eilbrt. 
We may thus obtain variations of a JiJ'tk in the tone of the 
muscular sound. 

We shall also see hereafter how the electric state of the 
muscles in contraction proves still more the complexity of this 

The conclusion at which we have arrived is, that during 
voluntary contraction, the motor nerves are the seat of suc- 
cessive acts, each of which produces an excitation of the 
muscle. The latter, in its turn, causes a series of acts, each 
of which gives birth to a muscular wave producing a shock. 
It is in the elasticity of the muscle that we must seek for the 
cause of the coalescence of these multiplied shocks; they are 
extinguished just as the jerks of the piston of a fire engine 
disappear in the elasticity of its reservoir of air. 

Of work done by the muscles. After having seen how 
mechanical force is produced, let us try to measure it that 
is to say, to compare it with the kilogrammetie. the unit of 
measure of work. If we suspend a weight to the tendon 
of a muscle which we cause to contract, we easily obtain the 
measure of work by multiplying this weight by the height to 
which the muscle raises it. 

In animated motors, the measure of work is less easy to 
obtain. Sometimes, indeed, the strength cf an animal is 
utilized in the lifting of a weight, but the greater part of the 
acts in which the strength of animals is employed can only 


be estimated by enlarging the definition, of mechanical work. 
Thus, a horse which tows a boat, a man who planes a board, 
a bird which strikes the air with its wing, does mechanical 
work, and yet they do not lift weights. In order to reduce 
cases of this kind to a general definition, we must admit as 
the expression of work, the effort wuhijilied by the spnce traversed. 
This effort, besides, may always be compared with the weight, 
the lifting of which would necessitate an equal effort, so that 
we say of a traction or an impulse, that it corresponds with 
10 or 20 kilogrammes. When a workman planes or turns a 
piece of metal, if the tool which he drives into it penetr.ctes 
only on condition of receiving an impulse of one kilogramme, 
the workman, in order to have effected a kilogrammetre of 
work, ought to have detached from the mass a shaving of a 
metre in length. A horse which tows a boat with 20 kilo- 
gramme force, will have employed a force of 20,000 kilo- 
grammetres when he has gone 1,000 metres. 

But still that is not yet sufficient to be applied to all the 
forms of mechanical labour. If, for example, force be em- 
ployed to displace a mass, the effort necessary for the move- 
ment will vary with the speed which is given to that mass. 
Let us imagine a block of stone suspended freely at the end 
of a very long rope; the lightest pressure applied to this 
block for a few instants will produce movement in it, while 
the strongest blow of the fist will scarcely cause any sensible 
displacement, because the force requisite to displace masses 
increases according to the square of the speed which is com- 
municated to them.* 

A force of very short duration applied to a mass, produces 
only a shock incapable of displacing it. But this same shock, 
if it be exerted by means of an elastic medium, is transformed 
into an act of longer duration, and without having added 
anything to the quantity of motion, becomes capable of pro- 
ducing work. 

This elasticity intervenes in the animal economy to permit 
the utilization of the very brief act which constitutes the 
formation of the muscular wave. The formation of the wave, 

* Tins action is expressed liy 



which, lasts only for some hundred ths of a second, represents 
the time of application of eacli element of the force of the 
muscle. At each new wave, there would be produced a true 
sJwck if the elasticity of the fibre did not extinguish this 
abruptness, and transform these jerky little contractions into a 
gradual increase of tension whicli constitutes the prolonged 
effort of the muscle. 

A 7iiotor only works on the double condition of developing 
an effort, and accomplishing a motion. Thus a muscle \vhicli 
contracts, performs no external work, except while it is con- 
tracting; as soon as it has reached the limit of its contraction, 
it ceases to work, whatever may be the effort whicli it 
develops. When we sustain a weight after having 1 lifted it, 
the act of sustainment does not constitute work. 

But, in these conditions, to maintain the elastic force of the 
muscle, the same acts are produced in its interior as during 
the work; the muscular waves succeed each other at short 
intervals, and heat is disengaged by chemical action. No\v, 
this heat, whicli cannot transform itself into action, ought 
to remain in the muscle, and heat it strongly. This is pre- 
cisely what we observe, so that in the malady called tetanus, 
whicli consists of a permanent tension of the muscles, it 
is ascertained that heat is produced with an exaggerated 
intensity, the temperature of the entire body rising several 




Electricity is produced in almost all organised tissues Electric currents. 
of the muscles and the nerves Discharges of electric fishes ; old 
theories ; demonstration of the electric nature of this phenomenon 
Analogies between the discharge of electrical apparatus and the shock 
of a muscle Electric tetanus Eapidity of the nervous agent ill the 
electrical nerves of the torpedo ; duration of its discharge. 

MOST of the animal or vegetable tissues are the seat of 
chemical actions, whence result an incessant disengagement 
of electricity. In this way, the nerves and muscles of an 


animal furnish manifestations of dynamic electricity. Mat- 
tr.ucei lias discovered the manner in which the muscular 
current is usually produced. Du Bois Reymoiid has added 
much to our knowledge of this current, of its intensity, and 
of its direction in every part of a muscle. Treatises on phv- 
siology give copious details of experiments relative to nervous 
and muscular electric currents. This study lias been the 
limn- eagerly pursued becausa the proximate cause of the 
function of the nerves and muscles \vas expected to be found 
in these electric phenomena. 

The most interesting fact connected \vilh muscular elec- 
tricity, \\ith respect to the transform a I ion of force, appears to 
be the disappearance of the electrical slate of a muscle at the 
moment when it contracts, or \\hen it is tetanized. It appears 
then that the chemical actions of which the muscles are the 
seat, are entirely employed in the production of heat and 

To observe these phenomena, we must make use of a very 
sensitive galvanometer. Suppose a muscle connected with one 
of these instruments; it gives its currents, and deflects the 
magnetic needle a certain number of derives. When this de- 
viation has been effected, and the needle has become stationary 
in its new position, it is only necessary to produce tetanus in 
the muscle, and immediately the needle retrogrades towards 
zero. This is what I)u Bois Reymond calls the iicyntive nn-'in- 
tion of the muscular current. The same phenomenon is 
observed in the voluntary contraction of the muscles. 

The interpretation of the negative variation is very im- 
portant. Du Bois Reymond having remarked, that for a 
single muscular shock no deflection of the needle from zero is 
obtained, concluded that this is on account of the short dura- 
tion of the electrical disturbance accompanying a shock, lu 
tetanus, on the contrary, a series of modifications in the 
electrical condition of the muscle correspond to the series of 
shocks produced their accumulated influence, deflects the 
magnetic needle. 

This phenomenon is familiar to physicists. It is known 
that the needle of a galvanometer suljectod to a IVequenily- 
iutermpted current, takes a fixed position intermediate be- 


twoen zero mid llie extreme point wliich it would have occupied 
it' the current h;id been continuous. 

In the muscles in which the shock is protracted, as in 
the tortoise, a very prolonged change in the electrical state is 
produced; and therefore these muscles can by each of their 
shocks cause a deflection of the magnetic needle. It is the 
same with the movements of the heart; each of these appears 
to be only a shock of the cardiac muscle, and yet it deflects the 
magnetic noedle in the same manner as tetanus of an ordinary 
muscle. This fact, that a negative variation is equally seen 
iu a muscle wliich is contracted voluntarily, is of the greatest 
importance. It confirms the theory which assimilates con- 
traction with tetanus, that is to say, with a discontinuous or 
vibratory action. 

One point which hns been long under discussion relative 
to the manifestations of muscular electricity, is whether the 
negative variation is caused by a change of direction in the 
111 use ul tr current, or by a transitory suppression of this 
current. The latter hypothesis lias been rendered extremely 
probable by the numerous experiments in which the needle 
of the galvanometer has never been seen to retrograde beyond 
the zero point. Thus the phenomenon of negative variation 
seems to prove the principle which we laid down at the com- 
mencement of this article, that force is manifested in the 
muscles in a different manner during activity and repose, and 
that the manifestation under the form of mechanical work is 
substituted for that under the form of electricity. 

Electric fishes. Animal electricity appears in a much more 
striking form in the discharges produced by certain fishes. 
In this case the special organs have for their object the pro- 
duction of electricity; nevertheless, by their structure, their 
chemical composition, and their dependence on the nervous 
system, these organs remind us of the conditions of the mus- 
cular apparatus. 

The number of species provided with electrical organs 
which was formerly restricted to five,* has been remarkably 

fr The five species formerly known were the Baya torpedo, tlie Gym- 
notus electricus, the Silurus electricus, the Tetniodon electricus, and the 
Trichiurus electricus. 


increased since Cli. has shown that ail the species of 
the genus ray have electrical apparatus and functions in a 
more or less rudimentary condition. Besides, the analysis 
of tins singular act, which is called the electric discharge, has 
been better studied, as physicists have then selves learned the 
different properties of the electric agent. 

In the 1 8th century, they said, when speaking of the torpedo, 
"this fish when it is touched throws out a kind of 
venom which paralyses and benumbs the hand of the fisher- 
man." Miischenbroec-k, in the List century, ascertained the 
electrical nalni-e of the torpedo's discharge. Walsh, in 1778, 
saw plainly that the numbness produced by this animal differs 
in no respect from that which is caused by the discharge of an 
electrical machine. He proved by a great number of experi- 
ments, that the effect produced by this fish is manifestly 
electrical. He subjected the discharge to a series of trials, 
in which it had the same effect as the electricity deve- 
loped by machine. For instance, he showed that the animal 
might be touched with impunity, by taking as a medium of 
communication non-conductors of electricity. Besides, he made 
the discharge pass through a chain of individuals holding each 
other by the hand, and all felt the same singular effect which 
is produced by the Leyden jar. 

At a later period Davy obtained with the current of the 
torpedo the deflection of the galvanometer, the magnetization 
of steel needles placed within a spiral of brass wire traversed 
by the discharge, and the decomposition of saline solutions. 

Becquerel and Brest-hot verified the same facts in the wire 
of the galvanometer, the current circulating from the back to 
the belly of the animal. 

The demonstration of the spark came still later. Father 
Liliari and Mattencci obtained this spark by breaking in 
various ways a metallic circuit through which the current of 
the torpedo was passing. The most ingenious process is that 
of Matteucci, who inside use of a file in the following manner : 
A metallic plate attached to a brass wire is fixed under the 
belly of the torpedo; on its back is placed a file on which the 
end of a metallic wire rubs. The animal is then irritated, 
and one or even several spaiks ;;ro seen in the daik to pass 


between the wire and the file. The production of the spark 
is probably effected when the circuit is broken at the precise 
moment of the passage of the torpedo's current. 

The use of the file is clearly seen, since the friction 
causing 1 the circuit to be closed and broken at very short 
intervals, some of them will necessarily coincide with the dis- 
charge, as it has but a short duration. Let us observe, in 
passing, that the production of two sparks during the discharge 
of the torpedo, shows very clearly that it has an appreciable 
duration, measured at least by the time which has elapsed 
during the passage of the wire across two successive teeth of 
the file. 

A. Moreau succeeded in collecting this electricity on a con- 
denser which allowed him to measure the variation of the 
intensity of the discharge by the indications of a gold leaf 
electroscope. We have seen how our acquaintance with iho 
electrical phenomena of the torpedo has passed through many 
successive stages, and how the progress of physical inquiry 
has, on this subject, invaded the domains of physiology. 

Nevertheless, the discharge of the torpedo, as the above- 
mentioned experiments have shown, seems like a kind of 
hybrid phenomenon, in which the effects of tension machines 
appear to be confounded with those of a galvanic battery. 
We must, by new researches, endeavour to assign the place 
in the series of well-known manifestations of electricity, which 
the discharge of electric fishes ought to cccupy. 

Considered in a physiological point of view, this phenor 
menon possesses another kind of interest. The most recent 
discoveries teud to assimilate the function of this electrical 
apparatus with that of u muscle. If, for example, we com- 
pare the action of the nervous system on the electrical organs 
of certain fishes, with that which the nerve exercises over the 
muscle, we are struck with the following analogies : 

The electrical discharges, like muscular shocks, can be 
produced under the influence of the will of the animal; they 
ma}' also be considered as reflex phenomena; excitation of 
the electric nerve produces the discharge, as that of the motor 
nerve produces, (lie shock of a muscle ; an eulire paralysis of 
the electrical apparatus takes place when the nerve is cut, as 


in a muscle v. hen its nerve is divided. This paralysis takes 
place also inider the influence of curare, although this poison 
appears to act more slowly on the electric nerves than on the 
greater part of the nerves of motion. Indeed, the electric 
tetanus, to employ the happy expression of A. Moreau, is 
manifested, not only when tha nerve of the torpedo is sub- 
j re ted to excitations very rapidly succeeding each otl:er, but 
also \vhen the animal is poisoned with str)ehnine or any 
other tetauizing substance. 

It was natural enough to compare the different cells or 
laminae of the electrical apparatus in fishes, with the elements 
of the voltaic pile, and following up this idea, to inquire what 
Avas the electro-motive power of each of these little elements, 
and what were the effects of tension resulting from the 
association of these pairs. The following is the result of (lie 
experiments of Matteucci. 

A portion of the electiical apparatus of the torpedo, placed 
en mpport with the extremities of a galvanometer, gives 
birth to a current of the same order as that in the apparatus 
of which it formed a part. The longer the prism thus 
detached, the more numerous must be the element* of this 
kind of animal pile, and the greater the deflection of the gal- 
vanometer at the moment of its discharge; this is produced 
by exciting the nervous fibre which conesponds \\ilh the 
simiU portion of the electrical apparatus of the torpedo pi. iced 
on the pads of the galvanometer. Thus far, the analogy of 
the electric apparatus with the pile is pcrlV- t, since the effects 
of tension increase with the number of elements which are 
employed. This analogy holds good with all the electrical 
fishes, \\hen we endeavour 1o compare the intensity of the 
curients obtained in diflerent pails of the apparatus. 

In the torpedo it is found that the di.-charges are at their 
maximum when we touch the two surfaces of iis apparatus on 
the inner side, that is to soy, at the thickest part, which con- 
tains the greatest number of di>cs superposed on each other. 
In the gymnotus. whose electrical prisms have so great a 
length, it is found (hut the discharge is stnmger still, on 
account of the greater volume and number of the elements. 
ID is proportional to the extent of space contuii.ed lotween the 


t\vo points which receive this impulse. In the silurus it is 
the same ; a much greater impression is made on us when 
we touch different points of the animal at a greater distance 
from each other. 

In fact, we may receive a discharge from a single surface 
of the electric apparatus of the torpedo, by touching un sym- 
metrical parts, that is to say, points where the number of 
Ilie elements of the pile is not so great, because of the 
different length of the prisms which compose it. Thus, 
although the polarity may be identical on the same surface of 
the apparatus, the fact of the inequality of electric tension 
on the different points of this surface suffices to create the 
possibility of a current, and to determine its direction. 

As to the origin of the electric force, we think that no one 
can now see anything in it but the result of chemical actions 
produced in the interior of the apparatus 

But be A ire they arrived at this opinion, physiologists ad- 
vanced many hypotheses as the source of animal electricity. 
Thus, when Du Bois llevmond had shown that the nervous 
tissue possesses an electro-motive force sufficiently powerfid, 
and that there exists in living nerves a current in a constant 
direction, it was thought that the voluminous nerves which 
belong to the electrical apparatus of fishes carry electricity 
to it, as the blood-vessels supply blood to the organs. Mat- 
ti'inti has demonstrated that a large lobe of the brain of the 
torpedo is the origin of the nerves belonging to its electrical 
apparatus. He lias observed that it is possible to remove all 
the rest of the brain, without depriving the animal of the 
power of giving voluntary or reflex discharges; but that it 
can no longer do so when this lobe is destroyed. Ho has for 
this reason named this the electric lobe of the torpedo. 

When a dying animal no longer gave spontaneous dis- 
charges, it was sufficient, said Matteucci, to touch the electric 
lobe in order to obtain discharges more violent than those 
which the animal gave voluntarily during the state of perfect 

Nevertheless, the notion of Matteucci has been exaggerated, 
when this thought was attributed to him, that electricity is 
formed in the brain of the torpedo, and is conveyed by its 


nerves. It is as much as to sny that the motive force is created 
in tlif brain and conveyed to the muscles by the nerves of 
motion. The electricity of the torpedo has its origin in the 
special organ of this fish as mechanical work is originated 
in a muscle. When we see the phenomena of electricity 
or of motion produced, the motive or electric nerves fulfil 
only the duty of transmitting the order received from the 
brain; but the electricity \vhich circulates in the nerves is 
not that which is manifested so energetically in the discharge 
of the apparatus. It is, says Matteucci himself, as if we 
were to confound the effect of the gunpowder with that of 
the priming which has been used in order to fire the charge. 

Thus, the most probable theory is that which assimilates 
the electric nerves to those of motion, the discharge to a 
muscular shock, the series of discharges to tetanus. 

In order to verify this theory, we have endeavoured to 
nsceitain* whether the nerves of the torpedo carry out the 
commands of the will with the same rapidity as the nerves of 
motion ; if, when the electric apparatus has received the order 
transmitted by the nerve, it hesitates, like the muscle, an 
instant before it re-acts (lost time) ; in fact, whether the dis- 
charge of the torpedo, contrary to those given by tension 
niiicliinps, possesses a certain duration which may be compared 
to that of the shock of a muscle. 

It has been seen, that heat, cold, the ligature of the arteries, 
and the action of certain poisons modify considerably the form 
and duration of the muscular shock. If experiment showed 
that as to its retardation, its duration, and its other phases, 
the torpedo's discharge corresponds with the shock of a muscle; 
if it is proved, that in both cases, the same agents produce the 
same eil'ccts, we should be right in assimilating still more 
n.iiipletely the electrical phenomena with those of motion ; the 
physiology of the former would illustrate, in many points, 
that of the latter. 

During a stay of a few weeks at Naples we have been 
able to sketch out this mode of inquiry, which has furnished 

Sir, fur tin- details of tlirsu c.\]ici iiuciits, " Journal Jo I'uuntomic et 
dc la physiologic." 


results as yet incomplete, but which tend to assimilate the 
electrical with the muscular action. These results are as 
follow : 

1. The rapidity of the nervous agent in the electrical nerves 
of the torpedo seems evidently to be the same as that of the 
nervous agent producing motion in the frog. 

2. The phenomenon called by Helmholtz lost time exists 
also in the electric apparatus of the torpedo, and lasts about 
the same time as in. the muscle. 

3. The discharge of the torpedo is not instantaneous, like 
that of certain kind of tension electrical apparatus, but it 
is prolonged about fourteen hundredths of a second ; which is, 
in a remarkable degree equal to the duration of a shock in a 
frog's muscle. 

We cannot enter here into the details of the experiments 
which have furnished these results, but we will endeavour, in 
a few lines, to explain the method which we employed. 

Registering apparatus measure the slightest intervals of 
time ; this we have seen in speaking of the estimated rapidity 
of the nervous agent. But, in order to employ the graphic 
method, we must have motion to give the required signal. 

Thus, in the experiment of Helmholtz, the muscular shock 
itself announced that the order of movement which the nerve 
had to convey had arrived at its destination. 

In order to obtain the signal of the electric discharge, we 
have employed it to excite the muscle of a frog, the shock of 
which was inscribed on the registering cylinder. 

The trace furnished by the frog signal is somewhat delayed, 
it is true, after the excitation has been produced ; but this 
delay is a known quantity, and it can easily be taken into 

The following is the method adopted to measure with the 
ordinary myograph the duration of the different acts which 
precede the discharge of the torpedo. 

In a preliminary experiment (fig. 12) the nerve of the frog 
was directly excited, and a note was taken of the time (e g) 
which elapsed between the instant (e) of the excitation, and 
the signal (#) given by the frog. 

In a second experiment the torpedo was excited, still at the 


instant (f\ and the electricity of its discharges was collected 
by means of conducting wires which scut it to the nerve of 
the//-"// siijiml. This would give its shock at the point (<). 

Fio. 12. Mrnur of tlio tinio wtv'ch elapses between the excitation of 

thu electric; nuive, and the discharge of the torpedo. 

The difference (g t] would express the time consumed by 
the torpedo between the excitation of its nerve and the dis- 
charge. By varying the experiment, as we have done for the 
motive nerves (page 43), we obtain the measure of the 
rapidity of the electric nervous agent, and that of the lost time 
in the torpedo apparatus.* 

Finally, in order to measure the duration of the electrical 
action, we had recourse to a method which consists in col- 
lecting this discharge during a very short time (l-100th of a 
second) to send it to the frog sii/nal, and varying gradually the 
instant at which the electricity of the torpedo was collected. 
It was thus ascertained that starting from the point (/.) one 
might, during 1 -1-lOOthsof a second, obtain a series of signals 
from the frog t', t", t'" , t"" , but that beyond that time the 
frog gave no signals, thus proving that the discharge had 

\Ve have not been able to follow out farther the compari- 
son "T Hie electric with the muscular action; but, according 
to the result, already furnished by experiment, we can foresee 

' Deprived iif appropriate apparatus, we have Leon olili^od to construct 
for oursehi > a kind <if registering instnimriit which should measure short 
intT\.ils "if time with snlliciciit precision. We refer the reader, for the 
i< il .!iT:iii'_'etiieiit ,,f the experiments, to the " Journal de r.-matomie et dc 
li phvMi'lo^ic," I...', cit. Fi^. 1'J represents tracings which one would 
i.lil.iin with tin 1 re-i>ti iin;_' instruments already known. 


that new analogies will still show themselves between these 
two manifestations of force in living beings, mechanical work 
and electricity. 



Of the forms under -which mechanical work presents itself Every 
machine must be constructed with a view to the kind of work which 
it has to perform Correspondence of the form of muscle with the work 
which it accomplishes Theory of Borelli Specific force of muscles 
Of machines ; they only change the form of work, but do not 
increase its quality Necessity of alternate movements iu living 
motive powers Dynamical energy of animated motors. 

If we have lingered long over the origin of heat, of 
mechanical work, and of electricity in the animal kingdom, 
it was in order to establish clearly that these forces are the 
same as those which are seen in the inorganic world. Certain 
evident differences must have struck the earlier observers, but 
the progress of science has shown, more and more clearly, 
this identity, which is now disbelieved only by those whose 
minds are still under the influence of obsolete theories. 

Mechanical force, to which our attention must now be 
exclusively directed, has hitherto been studied only in its 
origin ; we must follow it through all its applications to 
work of different kinds which it executes in animal me- 

In all the machines employed in the arts we must have 
organs which serve as media between the forces which we 
employ and the resistance which are required to be overcome. 
This word organ is precisely that which anatomists use to 
designate the portions which compose the animal machine. 
The laws of mechanics are applicable as well to animated 
motors as to other machines ; this truth, however, has to be 
demonstrated, but, like many ethers, it was for a long time 


Of the f< inns of tni'chnii'n-nl trnrk. When we liavo at our 
disposal a certain quantity of force, it is necessary, in order to 
utilize it, to collect it un IIT conditions which vary according 
to tin' nature of the effects which we desire to produce. 

We have seen that the measure of work actually employed 
i- tin- product of the resistance multiplied \>y the space 
through which it has to pass. Such a measure, being tlie 
product of two factors, may remain constant if the two factors 
\ary inversely. So that a considerable weight, raided to a 
slight height, will give the same result of work as a light 
weight raised to a greater height. 

These will be two different forms of the same quantity of 

work ; but, in this case, the form is of extreme importance. 

In order that the work (i]>]>lifd should be available, it is ne- 

ny that its form should be the same as that of the 

resisting force that is, of the work required to be done. 

If we have as a moving power a piston of a steam engine 
of largo diameter and short length, capable of lifting 100 
kilogrammes to the height of a centimetre, and that it is 
necessary with this generator of force to lift one kilogramme 
to the height of a metre, which equally represents a kilo- 
gram metre of work, the motive force in this machine cannot 
be utilized directly ; for at the end of the stroke of the piston 
the weight of a kilogramme will only have been lifted 
one centimetre, and T " " (r of the force at our disposal will re- 
main unemployed. Every machine, therefore, must be con- 
structed with a view to the special form under which the 
i. .-Mance to be overcome presents itself. 

It is true that by means of certain contrivances, levers or 
wheel-work properly is possible to cause a cer- 
tain quantity of work to pass from one form to another, and 
to apply it to the resistance to bo overcome. But this will 
be the object of ulterior Study. We have only to consider at 
this moment the case in which the force is directly applied 
to the obstacle which it has to surmount, which is a very 
In quent condition in animated motive powers. 

l.-t u- return, then, to the hypothesis in which the moving 
B of the piston ( ,f an engine mii-t be applied directly to 
n-.-i>tance. 1'nder these conditions the constructor 


will be cai'eful to give to the surface of tlie piston such an 
area, that the pressure on this surface may be precisely equal 
to the resistance which it has to overcome ; then he will give 
to the cylinder such a length that it will allow the piston to 
travel just as far as the resistance ought to move. It is only 
under these conditions that the machine will do the desired 
work, and utilize all its moving power. On the contrary, 
in the case in which work answering to a kilogramme! re 
must be done by lifting 100 kilogrammes to the height of a 
centimetre, the cylinder must be made so large that the pres- 
6ure of steam on the surface of the piston will develop an 
effort of 100 kilogrammes, and such a length only must be 
given to the cylinder, that the movement of the piston may 
be merely a centimetre. 

One cannot substitute one of these forms of cylinder for 
the other, for in one case the force would be insufficient, and 
in the other, the range would be too restricted. 

The only thing which is equal in both is the amount of 
work that the two machines can do, that is to say, the pro- 
duct of the force employed multiplied by the space passed 
through ; this is again the product of the surface of a section 
of the cylinder multiplied by its length, or, in other terms, 
it is the volume of steam contained in each machine, this 
vapour being supposed to be at an equal tension. 

This proportion of the volume of the matter which works 
to the work performed, is found in every case in which a 
moving force is employed. 

Two masses of lead falling from the same height will do 
work proportionate to their volume, or, which is the same 
thing, to their weight. Two threads of india-rubber of the 
same length, both of which have been stretched to the same 
degree, will do w r ork proportionate to their transverse sec- 
tions, and, consequently, to their respective weights. Lastly, 
two threads of the same diameter, but of unequal lengths, 
after having been subjected to the same elongation in pro- 
portion to their original lengths, will, as they contract, do 
work proportionate to their respective lengths, that is to say, 
to their weight. 

This leads to the consideration of muscle, which conforms 


rously to the g< neral laws which we have just enunciated. 
The larger a muscle is, that is to say, the more extensive is 
its surface, the more, susceptible it is of considerable effort, 
lint, on the other hand, a muscle contracts only in proportion 
to its own length. We may estimate that the mean shortening 
of a muscle while contracting, when it is not detached from 
the animal, is about a third of its length when in repose. It 
follows that the work done by a muscle will be in proportion, 
to its length and its transverse section-; that is to say, to its 
volume or to its weight. 

Thus, it is possible to ascertain, according to the anatomi- 
cal characters of a muscle, what is the force which it pos- 
sesses, relatively to that of other muscles of the same animal, 
and what is the form under which, its work is done. 

The substance of the muscles, that is to say, of red flesh, 
presents the same density in the different parts of the animal 
frame ; in consequence of which the weight is the most exact 
and the most expeditious method of estimating the relative 
importance of two masses of muscle, and of predicting the 
quantity of work which they are able to execute. 

As to the form under which muscular work must be pro- 
duced, it is deduced not less easily from the form of the 
muscle. If it be thick and short, it should produce a strong 
i ii'i ct multiplied by a short range ; if it be long mid slender 
it will have a more extended range, but will only develop 
feeble energy. 

There are many examples in proof of this law which 
regulates muscular action the sterno-mastoidal, the sarto- 
rius, and the rectus abdominis, are muscles of a long range, 
or, as it may be otherwise expressed, having a great ex- 
tent of movement; they have a fleshy portion of greater 
length. The lar^e pectoral muscle, the glutens maximus, 
or the temporal muscle are largo and short muscles, that 
is to say, capable of a considerable effort, but of slight 


Itorelli already understood the laws of muscular force; 
without the intervention of the imtinn of n-m-h, which was not 
introduced into mechanics at the time when lie lived; he 
made a very clear distinction between these two opposite 


characteristics of the action of a muscle according to the 
impulse of its volume or its length. And as a theory is 
al \vays required to satisfy the mind, this author sought to 
interpret these different effects by a theory of the structure of 
the muscles. 

Let us imagine, he, a minute chain of metal formed 
of circular elastic rings, and that an extensile force should be 
exerted on this chain. Each ring will change its shape and 
assume an oval form, and the whole chain will be lengthened 
in proportion to the number of its rings. When it recovers 
itself, under the influence of elasticity, the chain will grow 
shorter again in proportion to its length. The minute chain 
of Borelli is the primitive fibre revealed to us in the animal 
economy by the microscope. But, said Borelli, if we form a 
bundle of a great number of these chains, each one of them 
will resist the extensile force in proportion to the elasticity of 
its rings, that is to say, the thickness of the bundles, and the 
force with which the extended bundle will recover itself will 
be in the same ratio. 

We do not reason otherwise now that histology has shown 
us, in a muscle, a bundle of fibres whose actions are com- 
bined like the chains suggested by the Naples professor. 

Passing to other considerations, this author studied the 
influence exerted by the direction of the fibres on the force 
which they develop. He remarked that the muscles whose 
fibres converge obliquely on the same tendon, like the barbs 
of a feather on the central shaft, afford neither a range nor 
an effort proportionate to their length and their sections. We 
have no modification to make of this estimate of the composi- 
tion of forces in the muscular organ. 

Of the specific force of muscles. In the machines constructed 
by man, it is not enough to measure the longitudinal and 
transverse dimensions of the cylinder, in order to know what 
quantity of work each stroke of the piston will develop ; we 
must also know under what pressure the steam acts. That 
is estimated by the number of atmospheres it can lift as it 
escapes. At other times the force of the steam is measured 
by the number of kilogrammes of pressure which it exerts on 
every square centimetre of the surface of the cylinder. In 


every i .ise it is an estimate of the specific force of a certain 
volume of steam which is to he determined. 

In the same manner, in hydraulic machines, we must know 
the charge of water or its pressure, in order to ascertain the 
work which the machine can perform. 

Physiologists have also sought to determine the specific 
force of muscular tissue in different animals, and to compare 
with the unit of transverse section of muscle the effort which 
it can make. In this manner they have estimated that the 
muscle of the frog would develop an effort of 692 grammes 
}]. Wilier) for each square centimetre of section ; that human 
muscle would develop 1087 (Koster). In the bird the force 
would be about 1200 (Marey) ; in the insect it would be still 
greater (Plateau). 

According to Straus Durkheim, a muscle of the stag-beetle 
weighing 20 centigrammes would carry, if we measure the 
moment of power and that of resistance a weight of seven 

P>y such estimafes as these, we might compare animated 
moving powers with machines working under variable pres- 
sures. The frog, we might say, works with a pressure less 
than one atmosphere, man with a pressure greater than one 
atmosphere. There would be a greater pressure in the bird, 
i;nd still greater in the insect. 

Of nine/tines. When mechanical force cannot be directly 
utilixed, because it is not in harmony with the form of work 
which it ought to rll't ct, various means are employed in the 
arts to transform it. Machinery known under the names of 
wheels and levers are continually used for this purpose. In 
the animal organism contrivances are also found which change 
the form of the woik of the muscles. The lever is almost 
exclusively uscil by nature for this purpose. The arrange- 
ment of the bony levers which form the skeleton is so generally 
known that it needs no explanation here; but there is a veiy 
common error on thi> point, even among physiologists, which 
it is neces-.-iry to point out. 

Almost all the levei-s which arc found in the organism belong 
to the third order, that is to say, where the muscular force is 
upplied l,ct\\. -ii tl.e tul mm and the resistance. Under theso 


conditions, the effort that can be developed at the extremity of 
the lever is less than that of the muscle ; but the space passed 
through by this extremity of the lever is proportionately 
increased, so that the product of the force multiplied by the 
distance remains the same. 

Thus, we find in a great number of standard treatises, a 
sort of accusation brought against nature, for having entirely 
wasted a great part of the force of our muscles by causing 
them to act under a disadvantageous leverage. It is true, 
that to extenuate this fault, they are willing to grant that 
this arrangement, unfavourable in an economical point of 
view, gives to our muscles an elegance which they would not 
have possessed, if for example, a long muscular band had 
extended from the sternum to the wrist. These mechanical 
and aesthetic notions ought to give place to more correct ideas. 
We must, above all, remember that a muscle produces work 
corresponding to its volume or its weight, whatever may be 
the proportions of the lever to which it is attached. The 
effect of the latter is only to regulate the form under which it 
produces the work, without adding to it or subtracting from 
it. An error of the same kind is often committed in con- 
sidering the part played by levers made use of by man in his 
work. It often happens that human force is unable to raise 
certain weights ; we have recourse in these cases to levers of 
the first or second order, in which we increase the power of 
the arm in the ratio of the longer to the shorter arm of the 

In this manner we utilize a motive force which could not 
produce external work if we endeavoured to bring it to bear 
directly on the resistance to be overcome. But a lever which 
amplifies the force exerted, diminishes as much the extent of 
the work produced ; it adds nothing to the work executed by 
the motive power. 

Before the notion of work had been introduced into 
mechanics, and when it was not clearly understood that it was 
impossible to increase by mechanism the amount of force at 
our disposal, many false ideas were entertained with regard 
to the part played by machinery. When we consider those 
gigantic masses of stone the pyramids of Egypt, or those 


enormous blocks, culled dolmeiis, which our forefathers 
erected in prehistoric times, it was admitted that these 
Titanic \\-orks pre-supposed a very advanced knowledge of 
mechanism. Even now it would require an immense time, 
or an army of workmen, to execute similar works by employ- 
ing only the force of man and that of animals. 

We must not imagine that the old Gauls or ancient 
Krvptians-were able to escape from the inevitable necessity of 
employing many men or an enormous lapse of time in these 
labours at the period when the only source of mechanical 
work was that derived from living beings. 

But Ave live under new and better conditions, thanks to 
the invention of machinery whi';h develops mechanical work. 
In addition to the utilization of natural motive powers, such 
as water courses and wind, man is now able to employ steam 
engines, by means of which a small quantity of fuel does the 
work of a great many animals. It is by these means that 
Egypt has succeeded in a few years in cutting through the 
Isthmus of Suez, an enterprise which, four thousand years ago, 
would have absorbed the ellorts of many generations. 

,Y< ' -I'fisitif of alternate, motion in liviinj motive powers. When 
the piston of a machine has reached, the end of its stroke, the 
steam \\hicli impelled it must escape, and the piston must 
return in the opposite direction to accomplish fresh work. 
In the same manner, the muscle, after having contracted, 
must be relaxed in order to act afresh. But mechanicians 
have found that in the alternate movements there is a loss of 
work. When a heavy object impelled forward with rapidity 
has to be brought back in the opposite direction, it is neces- 
sary first to destroy th" work which it contains, so to speak, 
under the form of active lorn-. Precisely in the same manner, 
when a limb suddenly extended is required to be rapidly bent, 
the momentum acquired must first be destroyed ; to do which 
requires an expenditure of work. 

To iMiard against this loss of motive power, mechanicians 
have recourse, as much as pnssiM.-, to the employment of 
Circular movements instead ol' motion to and fro. Thus, man 
who is so often inspired in his inventions by the arrange- 
ments of which nature offers him examples, deviates in thi* 


case from his model ; he endeavours to surpass it, and he is 
right. To make this understood we cannot do better than 
quote a passage in which L. Foucault compares the screw- 
propeller of ships to the organs of swimming in fishes : 

" In our machines," said he,* " we have usually a great 
number of parts entirely distinct one from the other, which 
only touch each other at certain points ; in an animal, on the 
contrary, all the parts adhere together; there is a connection 
of tissue between any two given parts of the body. This is 
rendered necessary by the function of nutrition which is 
continually going on, a function to which every living being 
is subject during the whole of its existence. We can, besides, 
understand the absolute impossibility of obtaining a con- 
tinued movement of rotation of one part on. another, while 
still preserving the continuity of these two parts." 

Thus, a profound difference separates mechanisms employed 
by nature from those invented by man ; the former are sub- 
ject to special requirement from which the latter can be freed. 
The muscle can only act under the condition of being attached 
by its vessels and nerves to the rest of the organism. No 
portion of the body, not even the bones themselves, which 
have the least vitality, can be free from this necessity. 

One might find, in the animal organism, many other 
mechanical appliances, the arrangement of which resembles 
that of machines invented by man, but with differences ever 
of the same kind as those which we have just described. 

For instance, the circulation of the blood is effected in living 
beings by a veritable hydraulic machine, with its pump, valves, 
and pipes. But the fundamental difference between this 
complicated mechanism, and machines constructed by man, 
arises from the absence of independent portions, and especially 
of the piston. The heart is a pump without a piston, and its 
variations of capacity are obtained by the contractility of 
the coats of the vessels themselves. With the exception of 
this difference, we find perfect analogies between the circula- 
tory apparatus of animals and hydraulic motive powers. Tho 
function of the valves is identical in both in spite of apparent 

* " Journal des Debats," Oct. 22, IS 45. 


"SVe have formerly noticed in the circulation of the blood an 
influence which regulates and increases the effective work of the 
cardiac pump ; it depends on the elasticity of the arteries.* 
In like manner, in hydraulic machines, man has recourse to the 
employment of elastic reservoirs, to utilize more fully the work 
of pumps, and to render uniform the movement of the liquid, 
notwithstanding the intermittent character of the motive 
power. This effect may be compared to that which we have 
before remarked in the elasticity of muscles. 

Dynamic energy of animated motors. Animated motive 
powers and machines are subject to the same estimation of 
work ; it is the dj-narnic energy of the former as compared 
with the latter. 

The production of external work corresponding to 75 kilo- 
grammetres per second, has been called the horsepower, or, 
in more general terms, the motive power of one horse, it being 
supposed that one horse could develop the same amount of 

But animal motors cannot work incessantly, so that the 
horse-power would represent at the end of the day a much 
greater amount of work than the animal could have produced, 
had it been employed as a motive force. 

Man is estimated much lower as to his dynamic energy, 
(jig- of a horse-power), and yet, if we only require from the 
muscular force of a man an effort of short duration, it will 
furnish dynamic energy exceeding that of a horse-power. la 
fact, the weight of a man is often more than 75 kilogrammes ; 
each time that the body is raised to the height of a metre 
per second, in mounting a staircase, the man has effected 
during this second the work adequate to one horse-power. 
And if, during several instants, he can give to his ascent the 
speed of two metres per second, this man will have developed 
the work of two horse-power. 

Thus, in our estimate of the work done by the greatest or 
the smallest animals, we must consider it as a multiple or a 
fraction of the ordinary measure of horse-power. 

* c; I'liVbioIo^ic medicalc Jc la tin nlutiou ilu s;i;jg." 




Each muscle of the body presents, in its form, a perfect harmony with the 
nature of the acts which it has to perform A similar muscle, in 
different species of animals, presents differences of form, if the 
function which it has to fulfil in these different species is not the 
same Variety of pectoral muscles in birds, according to their manner 
of flight Variety of muscles of the thigh in mammals, according to 
their mode of locomotion Was this harmony -pre-established ? 
Development hypothesis Lamarck and Darwin. 

THE comparison between ordinary machines and animated 
motive powers will not have been made in vain, if it lias 
shown that strict relations exist between the form of the 
organs and the characters of their functions ; that this cor- 
respondence is regulated by the ordinary laws of mechanics, 
eo that when we see the muscular and bony structure of an 
animal, we may deduce from their form all the characters of 
the functions which they possess. 

It is known that the transverse volume of a muscle corres- 
ponds with the energy of its action; that the athlete, for 
instance, is recognized by the remarkable relief in which each 
of his muscles stands out under the skin. But less is known 
concerning the physiological signification of the length of 
the muscles, that is to say, the less or greater length of 
their contractile fibres. And yet Borelli has already given 
the true explanation. In his opinion, as we have seen, this 
length of red fibre is proportioned to the extent of movement 
which the muscle is fitted to produce. 

This distinction between the contractile or red fibre and 
the inert fibre of the tendon is of the utmost importance. 
Experiment has shown that the muscles when they contract 
are shortened to an extent which represents a constant frac- 
tion of their length. We may, without erring from the truth, 
estimate at -^ of their length, the extent to which a muscle 


cm contract. I!ut, \\hatevrr may be tlic absolute value of 
this contraction, it is always in proportion to the length of 
red film- , that is the result of the nature of the phenomena 
which prodiN work in the muscle. 

Thus, every muscle whose two points of attachment are 
Misceptil'lc of being much displaced by the effect of contrac- 
tion, mn>t nei -es>arily be a long muscle. Oil the contrary, 
every muscle which lias to produce a movement of short 
extent must of necessity be a short muscle, whatever may bo 
the distance which separates the two points of attachment. 
Thus, the ili-xors of the fingers and toes are short muscles; 
but they are furnished with long tendons, which convey even 
to the phalanges of the ringers or toes the slight movement 
originated at a considerable distance at the fore-arm or the leg. 

It is easy to estimate, in the dead body, the extent of the 
displacement which a muscle can exercise on its two points of 
attachment. By producing the movements of flexion or 
extension in a limb, we can ascertain with sufficient exact- 
ness the extent by which they separate or draw together the 
osseous attachments of its muscles. In a recent skeleton we 
can also judge with sufficient accuracy of the amount of these 
movements by the extent to which the articulated surfaces 
can glide over each other. 

In examining the muscular frame of man we are struck 
w ith the extreme length of the sartorius muscle ; it is easy 
to be seen that no other can displace to such an extent its 
] "ints of bony attachment. The sterno-mastoidal and the 
HHI/IHUS rectus iibdoininis are, after this, the longest muscles ; 
thcM- also are muscles which have very extensive movements. 
"We might thus cause all the muscles of the organism to pass 
under review, and in them all we should see that the length 
of the red fibres corresponds with the extent of the movement 
which this muscle has to execute. But, in the study, we 
must be on our guard against a cause of error which would 
t n<l to arrange certain short muscles among those which are 

l;<>ivlli himself has noticed this cause ot error; ho lias 
i-houn how jH-iiiiij'iinn muscles, that is to say, those whose 
lil'M - .!! m-i iteil obliquely into the tendon, like the barbs of 


a feather into the common shaft, are short muscles which 
appear like long ones. These considerations are indis- 
pensable when we wisli to understand the action of the 
various muscles of the organism ; it is only by this means 
that we can estimate the real length of their contractile parts. 

Though the harmony between the form and the function of 
different muscles is revealed everywhere in the anatomy of the 
human frame, this harmony becomes much more striking if 
we compare with each other different species of animals. 
Comparative anatomy shows us, in species closely allied to 
each other, a singular difference in the form of certain 
muscles whenever the function of these muscles varies. Thus, 
in the kangaroo, essentially a leaping animal, we find an 
enormous development of the muscles of leaping, the ylutei, 
the triceps extensor cruris, and the gastrocnemial muscles. 

In birds the function of flight is exercised under very dif- 
ferent conditions in different species ; so, also, the anatomical 
arrangement of the muscles which move the wing, the pectoral 
muscles, varies in a very decided manner in different species. 
To show the perfect harmony which exists between the func- 
tion and the organ, it would be necessary to enter into long 
details of the mechanism of flight. The reader will find, 
farther on, explanations on this head. We will content our- 
selves with giving in a few words the differences which have 
been observed in the movements of the wing, and in the form 
of the muscles which produce them. 

Every one has remarked that birds which have a large 
surface of wing, as the eagle, the sea-swallow, &c., give strokes 
of only a slight extent ; that depends on the great resistance 
which, a wing of so large a surface meets with in the air. 

Birds, on the contrary, which have but very little wings, 
move them to a great extent, and thus compensate for the 
slight resistance which they meet with from the air; the 
guillemot and the pigeon belong to the second group. If it 
be admitted that the first-mentioned birds must make 
energetic but restricted movements, and that the second must 
inove with less energy, but with greater amplitude of stroke, 
the conclusion arrived at must necessarily be that the first 
ought to have large and short pectoral muscles, while in the 


second, these muscles should be long and slender. This is 
precisely what takes place ; we can be assured of this, by the 

Fia 1^ -Skeleton of :t fl:iniin " (:iftT Al|.li. 

thi t.Tliuiii vi TV sl.'.iil and Uccji, wLkli indicated tlio sizo 
und till; ftliultlKW.^ ! tlio ln.ctur.ll muscles. 



simple inspection of the sternum in different species ; for 
this bone measures, in some degree, the length of the pectoral 
muscles which are lodged in its lateral cavities. Thus, birds 
with long wings, havo a wide and short sternum ; the others 
have one which is long and slender. 

FIG. 14. Skeleton of a penguin : sternum very long, wing Very short. 

The comparison of homologous muscles in mammals of 
different kinds is not less instructive under the aspect in 
which we are now considering them. But one is often em- 
barrassed in this comparison by the difficulty of recognizing 
the homology. The discrepancies are sometimes so striking 



that anatomists have described under various names the same 
muscle in different species. 

Still, in the greater number of cases, the homology is not 
doubtful ; it is implicitly admitted by the fact of an identical 
designation being applied to certain muscles in different 
species. These are precisely the muscles which we shall take 
for an example, to show the harmony which exists between 
the function and the oryran. 

Fi<:. 1 Y -Skeleton of the wing and sternum of tlio sea-swallow (Hirundo 
ni:irin;i .-hmvintf the extreme shortness of the stenuim, aud the yiv:it 
length cif the wing. 

Thus the femoral biceps is easily recognized in all mam- 
mals ; and it varies considerably, especially in its Lower attach- 
ment. In certain quadrupeds it is inserted all along the leg, 
almost to the heel; in these animals the leg is never ex- 
tended upon the thigh ; in animals which have the power of 
leaping, the Lower attachments of the biceps is more elevated; 
it is .still more so in the siniiu', which can almost extend 
the leg upon the thigh and stand upright. In man the biceps 



is inserted high in the perinocum. If one can rely on the 
anatomical plates of Cuvier aiid of Laurillart, the negro has 
the perincoal insertion of the biceps not so high as in the 
white man, thus approximating to its position in. the ape. 

Neglecting at present the question why there should be 
I his variety in the attachment which regulates the motion of 
the biceps, let us content ourselves with considering the con- 
sequences which this arrangement may have upon its function. 
It is clear that during the movement of the flexion and ex- 
tension of the knee, each portion of the bone describes around 
this articulation an arc of a circle which is larger as it recedes 
from the centre of motion. It is equally evident that each of 
these points will move to a greater or less distance from the 
femur or the ischium, according to the extent of the circular 
movement which it. executes. And as great movements should 
correspond with long contractile fibres, we ought to find 
inequalities in the length of the biceps in different mammals. 

This is precisely what is observed. In man, whose biceps 
has its lower insertion very near the knee, the extent of the 
movements of the moveable attachments is not very consider- 
able, so the contractile fibre will have relatively little length, 
while the tendon will occupy a certain part of the extent of 
the biceps. In the ape, the inferior attachment of the muscle 
taking place lower down will consequently have greater mo- 
bility ; whence the necessity of a greater length of active 
muscle, which is effected by the tendinous part being shorter. 
In quadrupeds the tendon of the biceps almost entirely dis- 
appears, and the muscle is formed of red fibre throughout 
almost all its extent. 

The mrius itenms muscle of the thigh presents the same 
variability in its attachments and its structure. If we observe 
its arrangement in man (fig. 16), we see at once that the 
attachment of this muscle to the leg is very near the knee, 
and that its tendon is very long. Let us examine the same 
muscle in an ape (figs. 17 and 18), we find that its tibial 
attachment is much farther from the knee, and as a conse- 
quence of the more extended movements which this attachment 
executes, we find that the muscular fibre gains length at the 
expense of that of the tendon, which is extremely short. 



This variability in the point of attachment is still very 
noticeable in the Mmi-tendinosus muscle, which derives its 
name fr>m the fact that in man, about half of the length 

Fin. Hi. Mn-ic-1 s ,f tin; thi^'l: in 111:111. The xnr'< /(/'.< muscle (alxive) and 
tlir rectiu iiitrrnnt (hi-lowi. are darkly .shaded, that they may lie inure 
nsily n ni/.,'d 'I'll rcjtus intermix is, at its lower extremity, pro- 
vided with a l'>n^ ti'iidon; its tlcsliy |iart is sliort, which is in liarni'iiiv 
with thr sluiht I'Xlcnt nf inciM-MH'iit in this inus -I' 1 , the attachment f 
whi.-.i is MTV !! so t<> the knee. Tin; sai't"i'ius inusclo is i>rovided with 
a short tendon at its inferior attaehinent. 

of the musclo is occupied by the tendon. In fact, the inferior 
attachments of the scun-trinliHaxits in man is very close to the 
ar'iciilatiun of tlio km-e, but in apes, where it is attached 
ln\\cr <lo\\ 11, tin- mil-lie has almost entirely lost its tendon; 
it is altogether lost in the greater part of other mammals, in 
(lie ( 'u.iita, for example. 



We might multiply indefinitely examples which prove the 
perfect harmony between the form of the muscles and the 
characters of their functions. Everywhere the transverse 
development of these organs is associated with strength, as 
in the triceps of the kangaroo, or the masseters of the lion 

Fin. 17. Muscle of the thigh in the Magot ; rectus interims muscle almost 
entirely formed of red fibres ; the attachments of this muscle being at 
a considerable distance from the knee, give it a great extent of move- 
ment in bending the leg upon the thigh. Sartorius muscle, having a very 
short tendon. 

everywhere also, the length of muscle is connected with the 
extent of movement, as in the examples which we have just 

Is this harmony pre-established, or rather is it formed under 
the influence of function in different creatures ? In the same 
manner as we see the muscles increase in volume by the 
habit of employing energetic efforts ; we also observe them, 


under tho influence of more extended movements, acquire a 
L-re.iter length ' J . Can we see a displacement of the tendinous 
attachments of the muscles to the skeleton, under the influence 
of changes in the force of muscular traction ? Such is the second 
proUem which wo propose to ourselves, and which experiment 
should 1)0 called on to determine. 

FH: ]5. MiisHes of tlic tlifch of tlic foiuta TCcrtii-; intrrniis. inserted 

I'rnin tlin kni-r. ;iliiinst cntirrly \vitliiiul tciiilcni The 

s:irlnriu-i li:ivii ^ its M]|n>rinr ntt:icliinriit vrry fn>ni tin 1 ru\n fi umivil 

art ii MI lit ion, ii:i- v.-i-y extended movements ; it imi.-s. s in o.nsi .|\K'H ( 
a great Iciigtli df n x d tiliru, :uid not of tendon. 


The nafur.d sciences have derived at the present day a 
impulse from tho influence of the ideas of Darwin. 


Not that the opinions of the illustrious Englishman are yet 
universally accepted ; it has been recently seen with what 
vehemence the defenders of the prevalent theory reject the 
development Irypothesis. But the appearance of the Darwinian 
theory has excited long discussions ; to the arguments which 
Lamarck formerly brought forward in favour of the vari- 
ability of living beings, many others have been added by the 
partizans of development. On the other side, the old doctrine 
has been maintained with a passion which was little antici- 
pated, so that at the present day, naturalists are divided into 
two camps; almost all who have devoted themselves to the 
study of zoology or of botany have taken one side or the other. 

In one of these camps we find that the old school, those 
who consider the organized world almost unchangeable, have 
retrenched themselves. According to them, the very numerous 
series of animals and plants is limited to a certain number of 
species, unalterable t} r pes which have the power of transmit- 
ting themselves through successive generations, from their 
origin to the end of time. It is scarcely admitted that the 
species has the power of departing even slightly, and in a 
temporary manner, from the primitive type. Those slight 
changes, which are brought about by variations of climate or 
of food, by domestication, or some other disturbing force of the 
same order pass away when the species is again placed under 
the normal conditions of its existence. The primitive type 
then re-appears in its original purity. 

In the other camp the belief is entirely different ; the living 
being is incessantly modified by the medium which it inhabits, 
the temperature which it finds there, and the nourishment 
which it procures. The habits which it is forced to assume 
in order to live under now conditions cause it to acquire 
special aptitudes which modify its organism, and change the 
form of its body. And because hereditary descent transmits 
to descendants, Avithin certain limits, the modifications acquired 
by their ancestors, the species is modified by degrees. Lamarck 
was the author of this theory of development, to which Darwin 
and his followers have recalled the attention of naturalists. 
Darwin adds to these external influences, which can modify the 
species of animals, another cause which maintains and increases 


those modifications continually, when they are advantageous 
to the species. This cause is natural selection. 

If the chances of birth have given to certain individuals a 
plight modification which renders them stronger or more 
active, as the case may be, but altogether more fitted to main- 
tain the >>tritaalrft>r r.ristence, these individuals are destined by 
that VTY circumstance to reproduce their kind. Nut only docs 
their physical superiority increase their chance of longevity, and 
give them by that means more time to multiply, but, according 
to Darwin, the very existence of a physical superiority in an 
animal causes it to Vie preferred above others, for the purpose 
of reproduction. Thus the entire species would be improved 
by successive acquisitions of new qualities every time that an 
individual happened to be born with better endowments than 
the other representatives of this species. 

The struggle between the old school and that of development 
threatens to endure yet a long time, without either side finding 
a victorious argument to overcome the other. Every one 
knows the reasons which have been alleged on both sides, and 
for which, in their turn, geology, archaeology, zoology, and 
agriculture have been laid under contribution. "When and 
how will the strife end ? No one can as yet answer this ques- 
tion. Yet, if one might venture a prediction as to the issue 
of the combat, founded on the actual attitude of the adverse 
parties, one might predict the defeat of the old school. Their 
ranks are, in fact, thinned every day ; they evidently grow 
discouraged, and seem to avow their inability to furnish proofs 
of a scientific character, by sheltering themselves under an 
orthodoxy that has nothing in common with the dispute. 

One objection might perhaps be brought against both 
systems that of keeping too much to generalities in their 
discussions, aiid not bringing sufficiently into relief the promi- 
nent points of the debate. 

Thus, wo must allow that Lamarck is much too vague in 
hi> explanations, when lie attributes to outward circumstances 
the changes in the living organism. Uetween a need which 
is manifested and the appearance of a form of organ which 
corresponds to that need, there is a hiatus which his theory 
has not filled. Ho tells us that the animal species which we 


now see, so admirably adapted, each to the kind of life which 
it leads provided, according' to their necessities, with claws 
or hoofs, wings or fins, sharp teeth or horny beaks have 
not always lived under this form ; that they have gradually 
acquired these diverse conformations, which are at present in 
perfect harmony with the conditions under which they live. 
But, when we ask him to show us a modification of this kind 
in process of accomplishment under an external influence, the 
author of the "Philosophic Zoologique" has little wherewith 
to furnish us, except modifications of slight importance ; he 
objects that scientific observation does not go far enough back 
into the ages of the world. If we open the tombs of Mem- 
phis and show Lamarck the skeletons of animals identical 
with those which live in Egypt at the present day, he replies 
without being disconcerted: "It is because these animals 
lived under the same conditions as those which exist at the 
present time." The answer is _as good as the attack, but 
proves nothing. We might carry on the discussion for ever 
on such grounds as these. 

Darwin is more precise when he pleads in favour of natural 
selection. There is no one at the present time who does not 
admit the enormous power of selection in modifying the type 
of organized beings. Breeders have produced the most 
curious transformations in the animal kingdom, by choosing 
continually for the purpose of reproduction, individuals pos- 
sessing in a high degree the physical characteristics which 
they desire to impress on the race. Selection produces in the 
vegetable kingdom transformations of a similar kind ; so that 
Darwin has, without giving way too much to hypothesis, 
attributed the principal part in transformation to a selection 
which is made naturally, for the reasons that have just been 
given. But Darwin, as well as Lamarck, only considers under 
a restricted point of view the causes of the transformation of 
organized beings. Each of the two chiefs of this doctrine 
gives the greatest prominence to the cause of variation which 
he first has pointed out. 

The new school which, by a judicious eclecticism, endea- 
vours to make a due partition between these two kinds of 
influences, in order to explain by successive transformations 


the surprising variety of living beings, has already furnished 
important arguments in favour of development. But many 
NUT, ml* look with suspicion on these studies; they consider 
that the immutability and variability of animal species belong 
t< rhe domain of insoluble questions. 

It is true, that if we ask the partizans of development to 
prove experimentally the reality of their doctrine ; if we 
n quire of them, for example, to transform the ass specic-s into 
the horse or anything analogous to it, they are forced to avow 
their inability, and they reply that it is necessary, in order 
to (.'fleet this, to exercise modifying influences during millions 
on millions of years. It must indeed have been by very slow 
transitions that the variation of species has been effected, if it 
indeed has taken place. Consequently, in the absence of an 
experimental solution, the development hypothesis can neither 
be proved nor refuted. 

Learned men, whose minds are habituated to rigorous de- 
monstration, are not interested in such questions ; they have 
no scientific value in their estimation. And yet science meets 
with such every day. When an astronomer studies the in- 
fluences which may cause the heavenly bodies to move more 
slowly; when he predicts a modification of the orbit of tho 
earth after the lapse of some millions of years, or a lengthen- 
ing of the period of rotation of our planet changes which 
would affect all the inhabitants of the earth with a mortal 
chill this philosopher is listened to. When he speaks of a 
i iH^e, however slight it may be, of the retardation of a 
planetary movement, every one understands that if this cause 
should continue during many ages, its effects will be exag- 
-. era ted by the lapse of time. No one tells this astronomer 
to \\ait till some millions of years have proved tho accuracy of 

Why should () be more unjust to the theory of develop- 
ment ' J . It cannot, it is said, bring before our eyes the trans- 
I iiuation of one animal into another. This is true, but it 
may show us some tendency to this transformation. However 
.slight it may In-, M-( accumulating more and more during 
many ages, it may bec..ine as complete a transformation as 
\\ 6 can imagine. 


But what we have a right to demand of the advocates of 
development, even now, is that they should show us this 
tendency ; that they should bring it before us under the form 
of a slight variation in the anatomical characters of individuals 
when exposed to certain influences, which continued from 
generation to generation, would in the end produce the most 
important modifications in the species. No one denies that 
the morphological characteristics of individuals are transmitted 
in different degrees to their descendants. The point which 
is to be demonstrated is the manner in which an external 
cause acts in order to impress on the organism the primary 
modification. Researches of this kind belong to experimental 
physiology, and this science may even now furnish us with 
some reliable arguments. 

At the time when Lamarck lived, scientific logic was not 
very exact in its requirements. In his opinion, a want which 
was felt, originated the organic conformation suited to satisfy it. 

A certain bird which was in the habit of seeking its food 
at the bottom of the water, made constant efforts to lengthen 
its neck, and its nec-k grew longer ; another bird wished to 
advance as far as possible into the waters of a pond without 
wetting its plumage ; the efforts which it made to extend its 
legs gradually gave them, the proportions observed in the 
wading birds (Grallatores) . The giraffe, attempting to feed 
on the foliage of trees, gained by this exercise cervical vertebree 
of a surprising length. 

Lamarck, certainly, attributed to hereditary descent the 
function of accumulating continually for the profit of the 
species that which each individual had acquired for his own 
benefit ; but he did not show what the slight acquisition 
was which was made by the individual himself, under the 
influence of external circumstances, and of the habits which 
he was forced to acquire. J. Hunter reasoned in a similar 
manner in sciences of a different order. When he wished to 
explain the cicatrization of wounds and the consolidation 
of fractured bones, he recognized the necessity that new tissue 
should be supplied by the blood ; but why did the blood 
carry these elements to the parts which needed them ? " It 
was," said he, " in virtue of the stimulus of necessity." 


We seek at the present dfiy to state with precision the rela- 
tion between causes and effects, to ascertain the gradual transi- 
tions which the animal or vegetable organism is ahle to pass 
through when it finds itself placed under new conditions. 
\Ve have a glimpse of the influence which function exercises 
over the organ itself which produces it. The short and pithy 
f'oniiula of Mons. J. (iucrin, "Function makes the orgnn," ex- 
presses in a' general manner the modifying action of function. 
This formula will acquire additional force when supported by 
individual examples. 

It must be shown' how the bones, the articulations, the 
muscles are, modified in various ways by the effect of func- 
tions of different kinds; how the digestive apparatus, yielding 
to very varving kinds of food, passes through transformations 
which adapt it to new conditions ; how a change effected in 
the circulatory function produces in the vascular system cer- 
tain anatomical modifications which may be predicted before 
they take placr> ; how the senses acquire new qualities by 
exercise, or lose by desuetude their former powers. These 
changes of function under the influence of the function itself 
are accompanied by anatomical modifications in the apparatus, 
physiologically modified. 

The first demonstration to be furnished will be to ascertain 
one of these transformations, and to show that it is always 
produced in a certain manner under certain circumstances. 
And if, in the second phase of the experiment, it can be 
proved that hereditary descent transmits even the least part 
of the modification thus acquired, the development theory will 
be in possession of a solid starting-point. 

This seems to be the true course, to follow, if we desire to 
obtain a solution of this important question. During several 
vears serious efforts have been made in this direction. Having 
been ourselves for a long time conversant with the problems 
of animal mechanism, we have often been induced to reflect 
on the reciprocal relations of the organs of locomotion and of 
tin -ir functions. We will therefore attempt to show how the 
skch-ton and the muscular apparatus harmonize with the 
movements of each animal under the ordinary conditions of its 



Reasons which have caused the skeleton to be considered the least variable 
part of the organism Proofs of the yielding nature of the skeleton 
during life under the influence of the slightest pressure, when long con- 
tinued Origin of the depressions and projections which are observed 
in the skeleton Origin of the articular surfaces Function rules the 

ANY one who examines the skeleton of an animal, and holds 
iu his hands its osseous portions as hard as a stone ; who knows 
how these bones have survived the destruction of all the other 
organs, and how they can remain, after the lapse of thousands 
of ages, the only vestiges of extinct animals, may naturally look 
upon the skeleton as the unchangeable part of the organism. 
This skeleton, he argues, is the framework of the body, and 
the soft parts are grouped around it as best they may, reposing 
in its cavities, spreading over its surfaces, but alwaj's obey- 
ing a law stronger than their own, and arranging themselves 
in the spaces which have been allotted to them among the dif- 
ferent portions of the bony structure. 

The observer, however little he may be acquainted with 
anatomy, _soon perceives on the surface of the bone a thousand 
curious details ; he sees there numerous small hollows, little 
abodes which seem to have been destined to receive or to shelter 
some organ that has disappeared. These hollows correspond 
with the origin of the muscles which adhered at these points to 
the excavated bones. Elsewhere there are deep rounded grooves 
which remind one of the channels found in the curbstones of 
ancient wells. A cord has also passed in that direction ; it was 
the tendon of a muscle which incessantly glided along that bone. 
But at the two extremities of this humerus the bone is polished 
as if by friction ; in the upper part it is rounded like a 
sphere, and it is lodged in a cavity of the shoulder-blade which 
it exactly fits. One would say that the movement of these 

SG ANIMAL MK( 1 1. \NI>M. 

bones hail worn the surfaces smooth; the humcrus continually 
( -lumping its position, and turning upon its axis, seems to 
imitate tin' action AVC employ when we wish to obtain by 
means of friction a body of a spherical form. 

It is thus, for instance, that opticians produce the forms 
and the polished surfaces of convex and concave lenses. At 
its lower end the shoulder-bone shows the trace of the same 
phenomenon, a small spherical projection articulating it with 
tin- radius; it shows also that there existed movements of 
two kinds, and close by, we meet with a surface cut like 
the groove of a pulley ; this, in fact, only contributed to the 
Hex ion and extension of the fore-arm. 

If we examine the skull we meet with fresh surprises; here 
every want is foreseen. Deep cavities lodge in their interior 
the brain and the organs of sense. 

The nerves have conduits which allow them to pass through ; 
each vessel creeps along a furrow which forms a canal for it, 
and is ramiiicd with the minute arteries whose rich foliation it 
delieately traecs out. 

If the bone were not so hard, one would really suppose that 
it had been subjected to external force, of which it bears, as it 
were, the impression. 15 ut it is in vain to press a bony sur- 
laee ; it resists absolutely the force which is applied to it. It 
is necessary to use a saw or a gouge if we wish to make a 
channel in it. How could the pressure of soft parts hollow 
out these cavities which are sometimes so deep ? 

The foresight of nature has prepared everything in the 
skeleton so that it may be disposed in the best possible manner 
to receive the organs to which it oilers its solid and invari- 
able support. Such is the natural argument of all those 
who have not seen, with their own eyes, these osseous changes 
take place, and these channels hollowed out. The anatomist 
as well as the zoologist have necessarily reasoned in this 
manner. They have considered the skeleton as the unalterable 
element of tlie organism, and therefore they have derived from 
it the ^.renter part of the speeifie characters in zoology. 

It must he v.-ry dilliciilt to oppose an opinion which has 
been lor a long time received. Thus, when Mons. C'harles 
Martin, carrying out and rectifying the ideas of Vic. d'Azir, 


has shown that the humerus of a man or of an animal is the 
homologue of the femur, but of a femur twisted on its axis, so 
that the knee turned behind becomes an elbow, zoologists 
have replied that this torsion was purely virtual. Instead of 
being the effect of a muscular effort, whose slow and gradual 
action has reversed the axis of the bone, this singular form 
is, in their opinion, the result of a pre-established arrange- 
ment of the organism ; for the embryo shows a contorted 
humerus, before muscular action has been sufficiently developed 
to produce such a modification of its skeleton. 

We might, with greater show of reason, argue in a directly 
opposite manner. 

No one denies at the present day that the bony sj'stem is 
perfectly yielding in its character. These organs, which are 
so compact and so hard in the dead skeleton, are, on the con- 
trary, essentially capable of being modified while the organism 
is living. If we exert upon a bone a pressure or a tension, 
however slight it might be, yet if prolonged for a considerable 
time, it can produce the strangest changes of form ; the bone 
is like soft wax which yields to all external forces ; and we 
may say of the skeleton, reversing the proposition to which we 
have just alluded, that it is completely under the influence of 
the other organs, and that its form is that which the soft parts 
with which it is surrounded permit it to assume. 

We are indebted to medicine and surgery for the knowledge 
of important facts, of which many examples could easily be 
given. Thus, when an aneurism of the aorta is developed, 
and it happens to meet in its course the sternum or the clavicle, 
it does not stop at this barrier of bone, but perforates it 
in a few months. The substance of the bone is absorbed and 
disappears under the pressure of the aneurism ; it certainly 
resists less the effort of the invading tumour than do the softer 
parts the skin, for example. 

But this pressure of the aneurism differs in no respect 
from that of the arterial blood; the force with which tho 
aneurismal sac compresses and perforates the bones, is present 
in every part where an artery touches a bone. The same ab- 
sorption of the bony material still goes on, so that the artery 
hollows out for itself a furrow in which it lodges with its dif- 


ferent branches, an example of which is seen in the internal 
surface of the parietal bones of llio human skull. Even a vein 
is able to i'mm a considerable hollow in a Lone. The ab- 
nonual dilatation of those veins which are called varicose, and 
which is usually produced in the legs, is accompanied with a 
change of form in the anterior surface of the tibia ; the bone 
wears tlic impress of the dilated veins. "We cannot say that 
these osseous furrows enter into the pre-established plan of 
nature ; that the skeleton had originally these furrows in 
order to provide for the swollen state which should hereafter 
be produced. Surgeons know that these hollows are formed 
in the bone of an adult, which was in a perfectly normal state 
before accident had caused the varicose dilatation of the veins. 

It is a similar mechanism which forms along the bones the 
furrows imprinted by the muscles, and which gives to the 
perineeum, for instance, the prismatic form by which it is 

The hollows in which the tendons are lodged are not formed 
hi 'fun 'hand in the skeleton; it is the presence of the tendon 
which has hollowed them out, and which still maintains them. 
Should a luxation take place and change the position of the 
bone with respect to the tendon, the former furrow which is 
now empty is gradually effaced ; at the same time a new- 
furrow is fi ained, and by degrees assumes the necessary depth 
to allow the tendon to repose in its fresh place. 

But, it may be said, that the articular surfaces, so perfect 
in their structure, so well adapted to the movements which 
they carry on, are certainly organs formed beforehand. Here 
tin- bony surfaces are clothed with a polished cartilage 
moistened with a synovial lluid which facilitates their move- 
IIH 'lit still more ; all around them, fibrous ligaments prevent 
the bones from passing the limits allotted to them, and the 
Mirl'.iees from separating from each other. S<.> perfect an ap- 
paratu- could not be formed by the. function alone. 

\Vr have hero at least a proof of the foresight of nature 
and of tin- \\iMlnm of her plans. ii- turn oner more to surgery, which will show us that 
a Tier di>loi atioiis, the old articular cavities will be obliterated 
and disappear, \\hile at the new point where the head of the 


bone is actually placed, a fresh articulation is formed, to wliicli 
nothing will be wanting in the course of a few months, neither 
articular cartilages, synovial fluid, nor the ligaments which 
retain the bones in their place. Here again, according to the 
expression which we used just now, function has produced 
the organ. 

So much for the furrows formed in the bone. But how 
can we attribute to external influences those decided promi- 
nences which we observe everywhere on the surface of the 
skeleton, those apophyses, as they are called, to which each 
muscle is attached. 

The answer is not less easy ; it is sufficient to account for 
the formation of projections on the face of the bone, if we call 
into play an influence contrary to that which we know to be 
capable of hollowing out the indentations. We must admit 
that traction has been exercised on the portion of the bone 
where the projection is observed. 

The existence of traction on all the points in the skeleton to 
which muscles are attached is absolutely evident ; it is clear 
that the intensity of these tractions is proportional to the force 
of the muscles which produce them. Thus, it is precisely in 
the tendinous attachments of the stronger muscles that w r e find 
the more projecting apophyses ; a proof that the prominences 
iu the bone are intimately connected with the intensity of the 
eifort acting upon them. The right arm, more frequently used 
than the left, acquires more decided projections on its bony 
structure. When paralysis of a limb suppresses the action of 
the muscles, its skeleton is no longer under the influence of 
muscular power, and the apophyses become less prominent ; 
in fact, if paralysis dates from birth, the bone remains nearly 
in its foetal form, which function has not supervened to 

Comparative anatomy also confirms this general law that 
the longer the apophysis is, the greater energy it reveals on 
the part of the muscle which was inserted into it. 

Mons. Durand de Gros has clearly shown the influences of 
muscular function on the form of the torsion of the humerus 
iu different species of fossil and recent animals. Thus the 
huinerus in the mole, the ant-eater, and several other burrow- 


ing animals is scarcely recognizable, so thickly is it studded with 
ridges and projections, each of which gave insertion to a 
powerful muscle. 

The skull and the lower jaw in the earn ivora hear the traces 
of a powerful muscular action. lu the skull a deep hollow 
it-tains the impression of enormous temporal muscles ; all 
around the temporal depression, decided ridges were the solid 
points of attachment of the muscle ; again, a strong and long 
apophysis hy the side of the lower jaw shows the violent 
tractile force to which it has been subjected in the efforts of 

If the effects of muscular actions on the bones augment with 
the intensity of the force of the muscles, they do not vary less 
in proportion to the duration of their action. From infancy 
to old age, the modification of the skeleton goes on more and 
more, and even allows us, to a certain degree, to determine 
the age of the subject. 

Mons. J. Gncrin lias shown that in the old man the verte- 
brte have longer apopliyses, the ribs more angular curves, &c. 
Compare the cranium of a young gorilla with that of an adult 
animal; the form will appear to you so different that unless 
you had been told that the two skulls belonged to animals of 
the same species, you would scarcely have believed it. Of a 
rounded form in the young gorilla, it changes its shape in 
the adult ; it assumes a kind of ridge like the crest of a 
helmet ; this is the apophysis into which the temporal muscles 
are inserted. We should never finish if we were to point 
out all the modifications to which the skeleton is subjected 
in different species of animals ; modifications which from the 
beginning to the end of life become more and more marked. 

Medicine, in its turn, furnishes us with curious information 
as to these questions, by showing us the sudden development 
of accidental apopliyses which are called i-.rustoscs. In certain 
maladies which attack the entire body, we see the skeleton 
covered, in a great numlier of points, with accidental osseous 
projections; and almost all these prominences are developed at 
the points of attachment of the muscles, and as they increase, 
they extend especially in the direction in which muscular 
traction is applied. 


The curvature of the bones, or their contortion on their 
nxis, is a phenomenon which is frequently observed. I have 
mentioned that Mons. Ch. Martin has demonstrated that in 
all the mammalia, the huinerus is a contorted femur, whose 
axis has made half a turn upon itself; this contortion, accord- 
ing to Gegenbaiier, is less in the foetus than in the infant, 
and becomes still more marked in process of age. It is 
therefore partly effected by causes which are in action during 
life ; and if it be true that eve-ry foetus brings into the world 
a contorted humerus, it is not less true that this form may 
be considered as the effect of muscular action accumulated 
from generation to generation in terrestrial mammals. 

Articular surfaces are particularly interesting to study when 
\ve wish to ascertain the influence of function over the organs. 
1C we admit that the friction of these surfaces has polished 
them, and given them their curvature, it is easy, when we 
consider the movement which takes place in each articulation, 
to foresee the form which these surfaces ought to possess. 

The surfaces whose curvature has the greater number of 
degrees, will correspond with the more extensive movements. 
Moderate movements, on the contrary, will only produce sur- 
faces whose curvature will correspond with an arc of but few 
degrees. As a necessary consequence, the radius of curvature 
in the articular surfaces will be very short, if the move- 
ments are very extended; it will be very long if the movement 
is moderate. 

Let us examine, from this point of view, the articulations 
of the foot in man ; we see in the tibio-tarsal articulation a 
curvature of small radius, on account of the considerable move- 
ment of the foot on the leg. In the tarsus the radius of the 
curvature increases in proportion as the mobility of the bones 
diminishes. The scaphoid shows aiticuhir surfaces of a great 
radius ; the radius increases still more in the tarso-metatarsal 
articulations, in which the movements are very limited ; then 
it diminishes again in the articulations of the metatarsals 
with the phalanges, and of the phalanges with each other, at 
which point there is great mobility. 

Everyone knows that if the articular movement is only 
effected in one direction, the surfaces will curve only in that 


direction ; such arc tlie trochlear surfaces, of which the articu- 
lation of the elbow, the condyles of the j;i\v, &c., are examples. 
But it' tlie movement is ex < 'iited in t\vo directions at once, 
the surfaces will present a double curvature, and iu the case 
of an inequality in tlie amplitude of the inovenients, the radii 
of these curvatures will be unequal. Thus, iu the wrist there 
exist movements ,,{' Hrxioii and extension which are consider- 
ably extensive, but tlie lateral movements are restricted. The 
result of this is that in the elliptical head formed by the 
carpal bone, there is a curvature of small radius in the direc- 
tion of the inovenients of ilexion and extension, while, iu the 
lateral direction, the curvature belongs to a circle of much 
L:iv;iter radius. 

It is still more interesting to observe the articular surfaces 
of a series of animals in different classes and species. 
Similar articulations present movements of very different kinds, 
which must bring about no less important differences in the 
articular sin faces. 

Let us take, for example, the head of the humerus, and 
follow the changes of its form, in man, in the ape, the carni- 
vora, the herbivora, the birds. "\Ve shall see that the perfect 
equality of movement in every dinction which can be exe- 
cuted by the human arm corresponds with a perfect sphericity 
to the head of the humerus that is to say, a curvature of the 
same radius in every direction. Among apes, those which in 
walking throw a part of their weight usually on their anterior 
limbs, have the head of the humerus llattened at the upper 
part, as if by the weight of the body. Besides this, the 
movements which are required in walking being more ex- 
tended, the curvature of tlie head of the humerus in these 
animals presents its least radius in the antero-posterior direction. 
This modification is inure marked still iu the caruivora, and 
above all iu the herhivoia, the head of whose humerus, tlaf- 
tci.ed above, piv.M-nts its short radius of curvature in the 
direction of the movements which serve for walking, and 
which predominate in this articulation. 

Mirds possess, in the articulation of the shoulder, two 
movements ,,f unequal extent. One, by \\hidi thev spiv. id 
an 1 fold tlnir \\in;;s and \\hich carries thv i-lbo\\ 


near to the body, and sometimes very forward ; the other, 
usually more restricted, is made in a direction perpendicular 
to the former ; it is that which constitutes the stroke of the 


Curvatures of different radii correspond, therefore, to these 
two movements of unequal amplitude; to the greater move- 
ment of stretching and folding the wing a curvature of short 
radius corresponds ; to the less extensive movement which 
raises and lowers the wing during flight, there is a corre 
spending curved surface of very long radius. The result of 
this is that the head of the humerus in birds assumes the 
form of a very elongated ellipse, at the level of the articular 

But the movements of flight present in different species 
great variations of amplitude. Birds which have sail-like 
wings give but very small strokes with them, while the 
pigeon, at the moment when it takes flight, strikes its wings 
one against the other above and below, producing a clapping 
noise, -\\ hich is familiar to every one. 

To theso variations in the extent of the movements corre- 
spond varieties of surface in the head of the humerus, which 
iu birds with sail-like wings has a very elongated elliptical 
surface ; but in the pigeon it tends to the circular form, and 
vory nearly attains it in the spheniscus, an aquatic bird found 
iu. southern seas, and closely resembling the penguin. 

From all this we may gather, that in the form of the bony 
structure, everything bears the trace of some external influ- 
ence, and particularly of the function of the muscles. There 
is not a single depression or projection in the skeleton, 
the cause of which cannot be found in an external force, 
which has acted on the bony matter, either to indent it, or 
draw it forward. It was not, therefore, a metaphorical exag- 
geration to say, that the bone is subject, like soft wax, to all 
the changes of form which external forces tend to impress 
upon it ; and that, notwithstanding its extreme hardness, it 
resists less than the most supple tissues the efforts which tend 
to change its form. 

And will this new form, acquired by means of function, 
disappear with the individual? Will he not transmit even 


the slightest traco to his descendants? Will hereditary 
descent make an unique exception with respect to these ac- 
quin-il characters? TJiis appears very improbable, and yet 
ue must admit it, if we negative the development theory. 
\V- mist bring forward a contraiy hypothesis, which would 
rt-vtTso the ordiiii'vv laws of hereditary descent, if we refuse 
to certain anatomical characters the power of becoming trans- 


We have stated that the bony system is subject to external 
influences, and especially to those of the muscles, which im- 
press on each bone the form which we observe in it. The 
great variety of forms in the skeletons of different animal 
species corresponds, therefore, with the diversity of their 
muscular systems. Thus, whenever in animals of different 
species we find resemblances in certain bones, we may affirm 
that the muscles which were attached to these bones were 
also similar. Whenever we observe in an animal, on the 
contrary, a bone of a peculiar form, we may feel assured of 
a peculiarity in the muscles which were attached to it. 

J5ut if the muscle and the bone vary simultaneously, what 
can be the cause which influences them both ? It is under- 
stood that the skeleton, as it is modified, plays a passive part ; 
that it is subject to the form imposed upon it by the muscle. 
]>ut what gives to the muscle itself, an organ eminently active, 
and the true generator of the mechanical force by which 
the skeleton is in 'some de-ree modified, the particular form 
which is revealed to us by anatomy? 

We hope to demonstrate that the power to which the mus- 
cular system is subjected belongs to the nervous system. The 
nature, of the acts which the will commands the muscles to 
perform, modifies the muscles themselves, in their volume and 
their form, so as to render them capable- of performing the-e 
act* in the best possible manner. And, as this >/< ir.s.s/Y // 
which determines all the aciions of animal life. ii'u\erns the is this, which, according to tin- external conditions 
under which every living being is placed, inlliienres its form, 


and regulates it according to the laws which we must now 
endeavour to make known. 

Nothing in the organic form is under the dominion of 
chance. The specific varieties of living beings have been too 
often compared to the fancies of an architect, who, while 
adhering to an uniform plan, invents a thousand varieties of 
details, as a musician composes a series of variations on a 
given theme. 

In our present inquiry we may say that the great variety 
which is found in the muscular apparatus, whether in the 
different parts of the body of an animal, or in the homologous 
parts of animals of different species; for instance, varieties 
in the volume or the length of muscles; the very unequal 
partition of the red contractile fibre, and the inert, white, 
glistening fibre of the tendon ; that all this is entirely subject 
to the dynamic laws of muscular function. 

Adaptation of the form of muscles to the requirements of function. 
Normal anatomy can only furnish us with examples of the 
harmony which exists between the form of the organs and 
their habitual function. Experiment alone can show us that, 
by changing the function, we may bring into the form of the 
organs modifications which may harmonize them with the 
iiew conditions which may be imposed upon them. It will 
be easy to make experiments for this purpose. From the 
moment when we know in what direction the modification 
ought to be produced, in order to adapt the organ to the 
function, the changes effected in animals placed by us under 
conditions of peculiar muscular function, will derive an im- 
portant significance. But while we wait for the realization of 
this vast series of experiments, there ai'e some which we can 
employ even now. Experiments made ready to our hand are 
furnished by pathological anatomy. 

Medicine and surgery are full of information on this in- 
teresting subject. They show us, for example, that it is 
movement itself which keeps up the existence of the muscle. 
A long repose of this organ brings about first the diminution 
of its volume, and soon a change in the elements which com- 
pose it. Fatty corpuscles are substituted for the striated fibre 
which form its normal element; at last, these corpuscles, 


becoming more and more abundant, invade the entire sub- 
stance of tin- miiM-le. This phase of alteration, or i'atty dege- 
neration, is followed by an absorption of the substance of the 
mii>cle, which disappears entirely at the end of a certain 

Thus, not only docs the volume of the organ increase or 
diminish according as the necessities of its habitual function 
require a greater or less force, but it wholly disappears when 
its function is entirely suppressed. This effect is observed in 
paralysis, where all nervous action is destroyed; in certain 
cases of dislocation, which bring closer together the two inser- 
tions of a muscle, so as to render its action useless; sometimes 
even in fracture and anchyloses, which, by an abnormal con- 
nection, render the two extremities of a muscle immovable, 
and prevent any contraction of its fibres. 

l>ut what will happen, if the muscle, instead of losing all 
its function, only experiences a change with respect to the 
extent of the movements which it can execute ? After certain 
incomplete anchyloses, or certain dislocations, we see the 
articulations lose more, or less of their movements; as the 
muscles which command flexion and extension only need, in 
sinh cases, a part of the ordinary extent of their contraction. 

If the theory just enunciated be correct, these muscles ought 
to lose a portion of their length. In order to verify this fact, 
we have only to make a short exclusion into the domain of 
pathological anatomy. 

A warm discussion arose, some twenty years ago, as to the 
transformation which the muscles underwent in those patients 
who were alllicted with the deformity commonly known by the 
name of i-luli J'nat. Sometimes the foot is twisted upon the 
leg, so that the surface which should bo uppermost is next 
tin- -.-round; sometimes the foot is so forcibly extended that 
the patient* walks continually on its extremity. In all these 
- the muscles of the leg have only a very limited play ; 
they under-... ihi rel'c.iv, either fatty or fibrous transformation. 
Among tliise miiM-les, these which have no longer any action 
undergo Patty degeneration, and then disappear ; \\hile those 
whose action is partly pi. at rved, pn scut only a change as to 
the proportion ,,]' ,-,.,| iil, n . ;i nd tendon. lu the latter 


tlie contractile substance diminishes in length, and is re- 
placed by tendon, which often assumes a considerable develop- 

J. Guerin, when pointing out the fibrous degeneration of 
the muscles, thought that he saw in it the proof of a primi- 
tive muscular retraction, which would ultimately have pro-, 
duced dislocation of the foot. This eminent surgeon also 
thought that the alteration of the fibre was the only lesion of 
the muscles in club-foot. Scarpa maintained, on the contrary, 
that in the greater number of cases the luxation of the foot 
was the original phenomenon. 

As to the nature of muscular change, all surgeons at present 
ngree in admitting that it may have t\vo different forms, and 
that sometimes the muscle undergoes fatty degeneration, and 
in other cases it is transformed into fibrous tissue. We are 
especially indebted to the beautiful works of Cuvier, for our 
knowledge of the conditions under which each of those 
changes in the muscular substance is produced. 

An example will illustrate how the muscles are affected 
according as their function is suppressed, or simply limited 
in extent. 

The muscles of the calf of the leg, or gastrocnemiaus, aro 
two in number ; their attachments and their functions are 
very different. Both are inserted below in the calcaneum, by 
the tendon of Achilles, and are, consequently, extensors of the 
foot on the leg. But their superior insertions are different ; 
the solcus, having its insertion exclusively in the bones of the 
leg, has no other office than that of extending the foot, as we 
have said before. The twin gastrocnemii, on the contrary, 
being inserted in the femur, above the condyles of that bone, 
have a second function, that of bending the leg upon the 

Let us suppose that anchylosis of the foot has been pro- 
duced ; it entirely suppresses the function of the soleus, which 
passes through the fatty degeneration, and disappears. The 
two gastrocnemii are in a different condition ; if their action 
on the foot has ceased, .there still remains their function of 
bending the leg on the thigh ; these muscles have, therefore, 
only one of their movements reduced in amplitude. Con- 


sequently, under sucli conditions, the twin muscles lose only 
a part of the length of their fibres ; they undergo what sur- 
geons call partial fibrous transformation, a modification which 
is only a change of proportion between the red fibre and the 

Those who are accustomed to regard pathology as a com- 
plete infraction of physical laws, will perhaps be astonished 
to see us search among these cases of dislocation and anchy- 
losis for the proofs of a law which regulates the form of the 
muscular system in its normal state. It would be easy to 
show that these scruples have no foundation ; but it will be 
better still to bring forward other examples which may not lie 
open to the objections so often urged against the applications 
of medicine to physiology. 

It is again from J. Guerin, that we must quote the facts 
of which \ve are about to speak. 

When we examine the muscular system at different periods 
of life, we find that it varies greatly in its aspects. It seems 
that the muscles have di.-tinct ages, and that, formed at first of 
contractile substance, they lose by degrees, as they grow 
older, their red fibres, which are replaced by the white and 
glistening fibres of the tendon. 

Thus, the diaphragm of a child is principally muscular, 
while in the old man the aponeurotic centre, the true tendon 
of the diaphragm, is extended at the expense of the contrac- 
tile fibre. The substitution of tendon for muscular fibre is 
still more marked in the muscles of the leg in infancy; they 
are relatively much more rich in contractile substance than 
during adult age. In the old man, in fact, the tendon seems 
to invade the nm de, so that the portion of the calf of the leg 
which remains is placed very hijji, and is very reduced in 
length. The muscles of the lumbar and dorsal regions present 
the same character ; in old age they are poorer in red lilire, 
but richer in tendon. 

What then, is ih ' change which takes place in the muscular 
f'liicti-in during the diil'eient periods of life ? Kvery one knows 
that, except in the very rare cases in which the man keeps up 
the habit of gMimastic exercises, the muscular function be- 
comes UK re and more restricted at least, as far as the extent 


of movement is concerned. The articulations of the limbs, and 
those of the vertebral column, undergo normally a sort of 
incomplete anchylosis, which continues to lessen more and 
more the flexibility of the* trunk. 

Look at a young child tossing about at his ease : one of his 
movements is to play with his foot ; to take it in his hands 
and carry it to his mouth appears to him very natural, and as 
easy as possible. In the adult, the muscular force attains its 
maximum ; but the movements are not so extensive as in 
infancy; man has no longer, as is well known, the same 
flexibility in his limbs. 

The old man can neither stoop readily nor completely 
draw himself up ; his vertebral column has lost its supple- 
ness ; he takes only short steps ; to sit down on the ground, 
with the knees raised, is to him extremely difficult ; and if 
we examine the extent of flexion and extension in his foot, 
we find that it has become very limited. 

The function of the muscles, therefore, changes with the 
different periods of life, and becoming more and more restricted, 
employs continually less contractile fibre. It is thus that the 
muscular modification of which we have been speaking is 
naturally explicable. This modification, which consists in the 
increase of the tendinous element at the expense of red fibre, 
may be prevented by keeping up the extent of muscular 
movements, by means of suitable exercise. 

Let us now return to comparative anatomy. Since it 
shows us perfect harmony between the form of the muscles in 
different species of animals and the characters of muscular 
function in the same species, the most natural conclusion seems 
to be that the organ has been subjected to the influence of 

If the race-horse is modified in its form by the special exer- 
cise which is called training, is it not an evident proof of the 
influence of function on the anatomical characters of the 
organism ? And if a species, thus modified artificially, 
returns to the primitive type when replaced under the con- 
ditions from which it had been taken, is it not the counter- 
proof of the theory which assigns to function the office of 
a modifier of the organ ? 


These very facts are, however, interpreted in an opposite 
sense by the partisans of the invariability of species ; they 
seem to liiul an unanswerable argument in support of their 
c;:u^e, in the return to the primitive type, when the modifying 
influences have (rased. 

To what conclusion can \ve come when we meet with these 
contrary opinions? It must be that the partisans oi' develop- 
ment have not completed their task, and that they ought to 
add new proofs to those which they have already given. It 
is to experiment that the principal part belongs, while theory 
is not without its importance; by causing us to foresee in what 
manner a certain kind of function ought to modify a muscle, 
it will give its proper value to the modification which may 
subsequently be obtained. Indeed, without theory, the ex- 
perimenter can seldom recognize the modification which he 
has observed. We seldom find in anatomy anything but 
that which we seek for, especially when we have to do with 
slight variations like those which we might hope to produce 
in the organism of an animal. 

The experiments to be tried are tedious and troublesome; 
their plan, however, is easy to trace. 

If man, adapting to his necessities the domestic animals, 
has already succeeded in modifying their organization within 
certain limits, he has produced these changes, as we may 
say, fortuitously. Only intending, for example, to obtain 
draught horses or racers, it was not necessary to place 
the species under conditions entirely artificial. This must, 
ho\\ever, be done, if we aim at elucidating the problem of 
whieli wo speak, and of carrying to the farthest possible 
limit, changes in the conditions of the mechanical work of 

.Man has ntilixed the aptitudes of dill'erent animals, rather 
than sought to give them new ones. It would be necessary 
to do violence to the habits of animals, and to constrain 
them gradually to perform acts to which their organism is 
but slightly adapted. If, in order to get its food, a species 
with an organi/.ation unsuitable for leaping, should be com- 
pelled to take leaps of gradually greater height, everything 
leads us to supple, that it would acquire at length great 


facilities for leaping. If the descendants of these animals 
retained any of the power of their ancestors, they might per- 
haps, in their turn, develop still more this faculty of leaping. 
Graduating thus the effort imposed on this particular species, 
no longer in a utilitarian point of view, which there would 
be no inducement to surpass, but requiring indefinitely more 
force or greater extent in the play of the muscles, we might 
hope that the anatomical development would increase indefi- 
nitely, and that we might obtain something analogous to that 
which is now called the passage of one species into another. 

What we have said of the muscular function applies to all 
the rest. By modifj'ing in a gradual manner the conditions 
of the food of animals, as well as those of light and dark- 
ness, temperature, and atmospheric pressure under which they 
may be made to live, we may impress upon their organism 
modifications analogous to those which zoologists have already 
observed under the influence of climate, and of the various 
atmospheric conditions .and different altitudes in which animals 
have been placed by nature. These changes, brought about 
by well-managed transitions always tending to the same end, 
would have a chance of producing considerable transformations 
in animal organization, provided that, by persevering determi- 
nation, these efforts were indefinitely accumulated ; as in the 
case of breeders of animals, who use similar means for the 
production of selected kinds of stock. 

We will proceed no farther in the field of hypothesis, but 
we will, in conclusion, make an appeal to zealous experimen- 
talists. Many who have been convinced of the great import- 
ance of this enquiry seem already to be engaged in this 
enterprise. What question, in fact, can more nearly concern 
the human race than this : Can our species be modified ? 
According to the tendency which may be given to it, can it be 
directed either towards perfection, or degradation ? 





Conditions common to all kinds of locomotion Borelli's comparison- 
Hypothesis of the reaction of the ground Classification of the modes 
of locomotion, according to the nature of the point of resistance, in 
terrestrial, aquatic, and aerial locomotion Of the partition of muscular 
force between the point of resistance and the mass of the body Pro- 
duction of useless work when the point of n Stance is movable. 

THE most striking manifestation of movement in the dif- 
ferent species of animals is assuredly locomotion : the act by 
which each living creature, according to its adaptation to out- 
ward circumstances, moves on the earth, in the water, or 
through the air. Therefore it is more convenient to study 
movement with regard to locomotion, for we can thus observe 
it under the most varied types. 

At the commencement of these studies we ought to consider 
the general characteristics of the function which is to occupy 
attention, and to point out the general laws which are to be 
found in all the modes of animal locomotion. But what can 
bo more difficult than to ascertain the common features which 
unite acts so different as those of flying and of creeping, as 
the gallop of a horse and the .swimming of a fish? Still this 
lias been frequently attempted. liorelli has endeavoured to 
represent the various modes of terrestrial locomotion, by the 
different methods which a boatman employs to direct his boat. 

This comparison may, with some additional developments, 
serve to e.xplain the mechanism of the piincipal types of loco- 


Let us suppose a man seated in a boat in the midst of a 
tranquil lake. Under these conditions, his skiff will remain 
perfectly motionless. If he wishes to advance, he must find 
what is called a point of resistance. Suppose him to be fur- 
nished with a pole, he will plunge it towards the bottom of 
the water till it reaches the ground ; then, making an effort, 
as if to drive from him this resisting body, he will cause his 
boat to move in the opposite direction. This progression with 
the point of resistance on the ground is similar to the ordinary 
conditions of terrestrial locomotion. 

If the boatman be provided with a boat-hook, he will 
get his point of resistance under different conditions. Laying 
hold of the branches of trees, or the projections of the shore, 
he will drag his pole towards himself, as if to bring near to 
him the bodies to which it is fastened ; and if these bodies 
resist his efforts, the boat alone will be displaced and drawn 
towards them. 

Here are then two opposite modes of progression with 
bearings on solid bodies ; in one the tendency is to repel, in the 
other, to draw them nearer : the effect is the same in each case. 

But if the lake be too deep, or if the shores be too distant 
to furnish the boatman with the solid fulcrum which he had 
used before, the water itself will serve as a medium of 
resistance. The boatman, armed with a flattened oar, endea- 
vours to drive the water towards the stern of his boat ; the 
water will yield to this impulse, but the boat, impelled in 
an opposite direction, will go forward. The various kinds of 
paddles for steam-boats, the screw, in fact, all nautical pro- 
pellers, present this feature in common, of driving the water 
backward, in order to produce in the boat an impulse in the 
contrary direction, and to cause it to advance. 

Instead of an oar acting on the water, we may suppose the 
boatman provided with a much larger paddle with which he 
might drive back the air at the stern ; he will propel his 
boat on the surface of the lake. He might make progress 
also by turning a large screw like the sails of a wind- 
mill, or by agitating at the stern some large fan which would 
drive the air in the direction opposed to that in which he 
desired to force his boat. 

101- ANIMAL Mr.rllANISM. 

In all those modes of locomotion a force is expended which 
impels in opposite directions two bodies more or less resisting ; 
tin- one is tin. 1 fulcrum, the other the weight to be displaced. 

Old writers called the force acting on the boat n'-uctiun 
tln-y considered it as an effort emanating 1 from the soil, the 
water, or any resistance whatever to which the, effort of the 
rowers was applied. "We can now understand clearly that all 
the motive force is derived from the boatman. This force can 
have as its result, either the repulsion of two points to which 
it is applied, or their approach to eacli other. In these two 
cases one of the points may be fixed, it is then the other which 
will be displaced ; or the two points may be movable, and 
then, according to their unequal movubility, one of them will 
be displaced more than the other. 

This geteral principle can be applied to all cases of loco- 
motion; it will be Millie lent for us to notice that which is 
essential in all the types which we shall consider. 

The most natural classification seems to be that which is 
based on the nature of the point of resistance ; accordingly, we 
may distinguish three principal forms of locomotion terres- 
trial, aquatic, or aerial. But in each of these forms, what a 
variety of mechanism we shall meet with ! 

If it be true that walking and creeping are the two 
piincipal types of terrestrial motion, that swimming corre- 
sponds with the more habitual mode of aquatic locomotion, 
and fl'ght with aerial locomotion, it is not less true that in 
certain media many kinds of locomotion are employed. Thus, 
walking and creeping are used both on the earth and in the 
water; iliglit is habitually performed in the air, and yet 
certain birds take a decided Might in the water. 

In fact, if we were compelled to assign to every animal its 
particular type of locomotion, our embarrassment would he 
:< as it' we -\\ere classifying tlieso movements. Some, 
imlerd, move \\ith an Mpial facility on the earth, the water, 
and in the air. "We will not then-fore attempt a strictly 
methodical classification of the diHnvnt. modes of locomotion 
of which wo are about to take a rapid survey. 

/. i'1'ixtriiil Inriiiiintinn furnishes two principal tvpes: in one 
tin- dl'ort consists in pressing on the ground in the direction 


opposite to the intended movement; this is the more usml mode 
of locomotion ; walking, running, leaping, belong to this first 
form. For this purpose the limbs serving for locomotion are 
composed of a series of rigi 1 levers, susceptible of change in 
length ; they can be shortened by the angular flexion of the 
articulations, nnd they gro\v longer, by being drawn up. If 
the leg when bent touches the ground at its extremity, and if 
a muscular effort be made to produce the extension of the 
limb, this can only be effected by removing 1 to a greater dis- 
tance from each other the ground on which the extremity of 
the leg rests and the body of the animal which is united 
to the base of this limb; the ground offers resistance, and the 
body, yielding to the impulse, is displaced. Sometimes the 
displacement in terrestrial locomotion is effected, not by a 
change in length, but by a simple change of the angle formed 
between the limb which causes the motion and the body of 
the animal. 

In the second type, namely crcc]>iny, a tractile effort is pro- 
duced ; the animal lays hold by a part of its body on an ex- 
ternal fixed point, and then drags the mass of its bulk towards 
this point. Let us take a snail, and place it on a piece of 
transparent glass ; at the end of a few moments the animal 
begins to crawl. If we turn the glass over, we shall see 
through the plate the details of its movements. Throughout 
all the length of its body appears a series of transverse bands, 
alternately pale and deeply coloured, opaque and transparent. 
These bauds are transmitted by a continual motion, from the 
tail to the head of the animal; they seem like the spirals of 
a screw which turns incessantly in the same direction. It' we 
fix our attention ou one of these b.uids in the neighbourhood, 
of the tail, we sse it pass towards the head, which it 
teaches in fifteen or twenty seconds, but it is followed by 
a continued series of bands which seem to spring up behind 
it as it advances. These bands remind us of the muscu- 
lar wave and its progress through a contracting tibi'e, only 
with greater dimensions. E ich time that a wave arrives 
at the cephalic region of the animal, it disappears, producing a 
forward motion of the head, which slips a little on the surface 
of the glass and advances slightl}' without any retrogression. 


It appears that the cephalic region lays hold on tlio fixcil 
point touards which all the rest of the body is dragged for- 
\\;inl. In fact, in the posterior region an opj)osite phenome- 
non t.-ilccs place; each ue\v hand which takes its rise there, is 
accompanied l.y a backward motion of that region, which moves 
as if it were drawn by a longitudinal retraction of tlie con- 
tractile tissue. 

Other modes of creeping are not less curious; that, for 
example, which takes place in the interior of a solid body ; 
na a worm, when it advances in the tubular cavity which it 
has hollowed out in the ground. The hinder part of the body, 
soft and extensible, is assuredly of much less size than the 
cavity of the hole from which we endeavour to pull it, and 
\rt the worm resists the force of traction, and breaks rather 
iliati Le drawn out. This is because, within the ground, 
the anterior portion of the body, shortened but swollen, dilates 
within the passage, and finds there a solid point of resistance. 
If we let the worm go we shall see it rapidly shorten its 
body, and withdraw the rest, of it into the ground, being 
dragged backward towards the anterior portion which has a, 
firm hold on the soil. 

15y the side of the action of creeping we may naturally 
place that of climbing, in which the anterior limbs seek to lay 
bold of some elevated projection, and as they bend raise the 
of the body of the animal. The hinder part then fixes 
itself in its new posiiion, and the anterior limbs, thus set free, 
seek, higher up, a fresh resting place to make a new effort. 
What different types in these two modes of terrestrial locomo- 
tion ! The varieties are so great that we can scarcely give 
aa exact idea of them, except by describing the mode of pro- 
gression adopted by each particular animal. 

/ i-oniiilion in unti'r presents a still greater diversity. In 
-piie ease, \ve see a fish which strikes the water with the Hat 
of its tail ; in another, a cuttle fish or a medusa, which, com- 
pressing forcibly its pouch full of liquid, drives out the water 
in one direction and propels itself in a course directly opposite ; 
the same pin -non i en <>i i is pi odin-e-l wh -n a mollusk closes rapidly 
the Valves of its shell, and projects it self in the direction opposed 
to the cm rent of water which it lias produced. The larvie of 


dragon-flipspxpelfrom their intestines a veiy strong jet of liquid, 
and acquire, by this means, a rapid and forcible impulse. 

The oar is found in many insects which move oil the sur- 
face of the water. A contrivance is employed by other 
animals, which resembles the action of an oar used at the 
stern of a boat in the process called sculling. To this 
latter motive power may be referred all those movements 
in which an inclined plane is displaced in the liquid, 
and finds in the resistance of the water, which it presses 
obliquely, two component forces, of which one furnishes a 
movement of propulsion. This mechanism will require some 
explanation ; it will be found ia its proper place, with all 
the developments which it affords. 

Aerial locomotion. This mechanism is still the same ; the 
motion of an inclined plane, which causes motion through 
the air. The wing 1 , in fact, in the insect as well as in 
the bird, strikes the air in an oblique manner, repels it in a 
certain direction, and gives the body a motion directly oppo- 
site. With the exception of certain birds which spread their 
wings to the wind, and which, hr vering thus without any 
other effort than simply steering, have received the picturesque 
name of hovering or sailing birds (oiseaux voiliers), all 
animals move forward only by an (ffort exerted between t\vo 
masses unequally movable. It can be easily understood that 
if one of these points where the force is applied is absolutely 
fixed, the other alone will receive will cut diminution the 
motive work developed ; such is the condition of terrestrial 
locomotion on soil perfectly solid. But we can understand 
also that the softness of the ground constitutes a condition un- 
favourable to the utilization of the force employed, and that 
the extreme mobility both of the air and the water offer still 
less favourable conditions for swimming or flight. 

But this mobility of the point of resistance varies with the 
rapidity of the movement; so that a certain stroke of the 
wing or the oar, which would be without effect if produced 
slowly, would become efficacious by its very rapidity. 

In different kinds of locomotion, the resistance which it 
is necessary to overcome in order to displace the body, does 
not vary less than that which serves as an external point of 


resistance. This variability depends on many causes. Thus, 
different kinds of animals, when they move, have not to 
struggle with the same effort against their weight. The fish, 
which is of nearly the same specific gravity as water, finds 
itself su-pended in it without having to exert any force; 
and if it wishes to move in any direction, it lias only to 
overcome the resistance of the fluid which it is necessary 
to displace. The bird, on the contrary, if it desires to sus- 
tain itself in the air, must make an effort capable of 
neutralizing the action of its weight. If it moves forward 
at the same time, it must perform, in addition, the work 
which is consumed in overcoming the resistance of the air. 

Partition of muscular force between the points of resistance and 
the muss of the lodij. When, in physiology, we seek to es- 
timate the work of a muscle, we fix it firmly by one of its 
attachments, and we ascertain the extent passed through 
by its movable extremity. If we know the weight which 
this muscle can raise as it contracts, and the extent through 
which that weight is raised, we have elements by which we 
can estimate the work effected. But these are almost ideal 
conditions, which are scarcely ever found in terrestrial loco- 
motion; nor can we observe them in animals which move in 
the water, and more especially in those which fly through the 
air. Let us only compare the effort necessary to walk on a 
movable soil, on sandy dunes, for instance, with that required 
in walking on firm soil. We shall see that the mobility of 
iho resisting surface presented by the sand destroys a part of 
the dlort necessary for the contraction of our muscles; in 
other words, that a greater eff.rt is necessary to produce the 
same useful work, when the point of resistance is not stable. 

This amount of work is easy to be understood, and even to 
be measured. 

When a man, while walking, places one of his feet on the 
ground, the corresponding leg, slightly bent, draws itself up, 
and pressing on the ground In-low, gives at the same time an 
upward impulse to the body. If the ground entirely resist 
this pressure, all the movement produced will be in tho 
dim-lion ol' the trunk of the body, which will be raised 
to a certain height, three centimetres for example. But if 


(lie ground sink two centimetres under the pressure of the 
loot, it is evident that the body will only be raised one 
centimetre, and the useful work will be diminished by two- 

The compression of the soil under the foot certainly con- 
stitutes work, according to the mechanical definition of this 
word. In fact, the soil, as it yields, offers a certain resist- 
ance. This resistance must be multiplied by the extent to 
which the soil is indented, in order to ascertain the value of 
the work accomplished in this direction. But this work is 
absolutely useless with respect to locomotion : it is an entire 
loss of the motive force expended. 

When a fish strikes the water with his tail, in order to 
drive himself forward, he executes a double work ; a part 
tends to drive behind him a certain mass of fluid with a 
certain velocity, and the other to drive the animal forward in 
spite of the resistance of the surrounding water. This last 
work alone is utilized ; it would be much more considerable 
if the tail of the animal met with a solid point of resistance 
instead of the water which flies from before it. 

Is it possible to measure the dimiuution of useful work 
in locomotion, according to the greater or less mobility of the 
point of resistance ? 

If the ground on which we walk resist perfectly, it must be 
admitted that no part of the muscular work is lost; but in 
every case in which a displacement of the resisting surface 
exists at the same time as that of the body, it is necessary to 
determine the law according to which this partition is made. 
A principle established by Newton regulates the science of 
mechanics ; this is that " action and re-action are equal." 
Does this mean, in the case before us, that half of the work 
is expended on the resisting surface, and the other half on 
the displacement of the body of the animal? This cannot be 
true, if we may judge by the many cases in which a force acts 
on two bodies at the same time. 

Thus, in the science of projectiles, the motive force of the 
powder that is to say, the pressure of the gases which are 
disengaged in the cannon, acts at the same time on the pro- 
jectile and on the piece, giving these masses a velocity in 


opposite directions. Thus, the momentum (M.Y.) is equally 
divided between the two projectiles, .so that the mass of the 
cannon and of its carriage, multiplied by the velocity of the 
recoil which is commuuicuted to it, is equal to the mass of 
the projectile multiplied by the velocity of propulsion which 
it receives. As the cannon weighs much more than the ball, 
the velocity of its recoil is much loss thaii that commuui- 
cated to the projectile. 

As to the u-iirk developed b} T tlie powder against the cannon 
and against the ball, it is divided very unequally between 
these t \\ o masses. 

In fart, the work produced by an active force being pro- 
portional to the square of the velocity of the mass in motion 
(ils formula is '^'), calculation shows that this work, when 
the piece weighs 300 times more than the ball, would be 300 
t lines greater for the ball than for the cannon. 

We shall return to these questions, when in considering the 
particular kinds of animal motion, we enter on the investiga- 
tion of human locomotion. 



Choice of certain types in order to study terrestrial locomotion - Human 
locomotion Walking Pressure exerted on the ground, its duration 
and intensity Re-actions on the body during walking Graphic 
nirtlmd of .studying them Vertical oscillations of the body 
Jlnri/Diital oscillations Attempt to represent the trajectory of the 
pnlii.s Forward movement of the body - Inequalities ol ils velocity 
during the time occupied by a pace. 


TM K types of terrestrial locomotion are so various that wo 
must, fur a time at least, confine ourselves to the study of the 
most, important among them. For locomotion among liipeds 
we \\ill take as a type that of man. The horse will be chosen 


ns the most important representative of tlie method of walking 
adopted by quadrupeds. As to other animals, they will be 
studied in an accessory manner, and especially with reference 
to the resemblances and differences which the modes of their 
locomotion present when compared with the types which we 
have chosen. 

Many authors have already treated on this subject; from 
the time of Borelli to that of modern physiologists, science 
has slowly advanced : it seems to ns that it can now resolve 
all obscure questions, and determine them definitely, by the 
employment of the graphic method. 

While observation employed alone furnishes only incom- 
plete and sometimes false data, the graphic nn-tliod carries its 
precision into the analysis of the very complex movements 
concerned in locomotion. We shall see, when we treat of the 
paces of the horse, that the disagreement we find among 
writers on this sulject shows clearly the insufficiency of the 
methods hitherto employed. 

Human locomotion, though much more simple in its mechan- 
ism, is still very difficult to analyse; the works of the t\vo 
Webers, though considered as the deepest investigation of 
human locomotion that have yet been made, show many 
omissions and some errors. 

The most simple and usual pace is wit/lung, which, according 
to the received definition, consists in that mode of locomotion 
in which the bmlij never quits the ground. In running and 
leaping, on the contrary, we shall see that the body is en- 
tirely raised above the ground, and remains suspended during 
a certain time. 

In walking, the weight of the body passes alternately from 
one leg to the other, and as each of these limbs places itself 
in turn before the other, the body is thus continually carried 
forward. This action appears very simple at first sight, but 
its complexity is soon observed when we seek to ascertain 
what are the movements which concur in producing this 

We see, in fact, that each movement of the limbs brings 
under consideration a phase of impact and one of support in 
each of these ; the different articulations bend and extend 


alternately, while the muscles of the log and the thigh, which 
produce these movements, pass through alternations of con- 
traction and relaxation. 

The intensity of the pressure of the feet on the ground 
varies with the rapidity of walking 1 and with the length of the 
step. Besides this, the body passes through periodical oscil- 
l.itions, the re-action of the impact of each foot on the ground; 
and the different parts of the body are subject to this re-action 
in various degrees. These oscillations are produced in diffe- 
rent directions; some are vertical, others horizontal, so that 
the trajectory which follows any point of a body is a very 
complex curve. In addition to this, the body is inclined and 
drawn up again at each movement of one of tie legs ; it 
revolves as on a pivot round the coxo-femoral articulation, at the 
same time that it is slightly bent following the axis of the 
vertebral column; and, under the action of the lumbar muscles, 
the pelvis moves and oscillates with a sort of rolling motion. 
At the same time the anterior limbs, exerting an alternate 
balancing power, lessen (he influences which, at each instant, 
lend to cause the body to deviate from the straight course 
which it strives to maintain. 

All those acts have been analysed with much sagacity by 
one of our pupils, Mons. G. Carlet,* from whom \ve quote some 
of the results which he has obtained. 

The motive force developed in walking, its pressure oil the 
ground in one direction, and its propelling effects on the mass 
of the body on the other hand, are the three elements which 
\\ill at first occupy our attention. 

Motive force. This is found in the nclion of the exterior 
muscles of the thigh, the leg, and the foot. The lower limb 
forms, as a whole, a broken column, whose angles are rounded 
off, and whose return to the perpendicular is effected by pres- 
Mire on the ground below, and on the body above. This is all 
that we can say on this head, which, if treated more at length, 
\\ould require considerable amplifications. 

1'n'sani-e on the tjntunil. This piessure, equal, as we have 
leloii- si en, to that ill the opposite direction, which tends to 
impel the body loi \\ard, must, bo studied in its duili<>it, its 
(I. i';ir!it, Ktmlf .lr l.i M;nrhf. Anuales des Sciences nuturelles, 187'2. 



phases, mid its intensity. The registering apparatus enables us 
to do this perfectly ; an experimental instrument placed under 
the sole of the foot is connected with a lever which gives the 
signals of the impact and of the rising of the foot, as well as 
the expression of the force with which the foot is pressed upon 
the ground. We call this first instrument the experimental 
shoe, which may be thus described : 

Under the sole of au ordinary shoe is fixed with heated 
guita percha a strong sole of india-rubber lj centimetres in 
thickness. Within this sole there is au air chamber, which 
in tig. 19 is represented by dotted lines. 

FIG. 19. Experimental shoe, intended t'> show the pressure of tho foot 
on tlio ground, with its duration and its phases. 

Tliis chamber, having upon it a small piece of projecting 
wood, is compressed at the moment that the foot exerts its 
pressure on the ground. The air expelled from this cavity 
escapes by a tube into a dnun- with a lever attached, which 
registers the duration and the phases of the pressure of 
the foot. 

Let us suppose that the experimenter is provided on both 
feet with similar shoes, and that he walks at a regular pace 
round a table -which supports the registering apparatus ; we 
shall then understand the arrangement of the experiment. 

The registering instruments employed are already known to 
the reader; they resemble in all points those which have 

1 1 I- ANIMAL Mi:< 1IAXISM. 

served for the investigation of tin- muscular wave (fi. 7, 
pajje :17 . If\\e substitute in this ii^-iire an experimental 
shoe l'..r each <>!' tin- myographical flips 1 ami _', we shall 
have the arrangement of the apparatus necessary for the study 
..)' /' otstept or iiitjxH-ts of the foot on the ground. 

l-'iu-. _'() has lii-cii furnished }>y an experiment in walking. 
Txvti tracings arc ^iven by tlie intermittent pressure of the 
fret on the ground. The full line 1) corresponds with the 
ri-ht loot ; the dotted line with the left. 

Fin. 20. Tnuv'ngs >f the.' impact mid the riseof the two feet in our ordinary walk. 

Knowing the arrangement of the apparatus, we can under- 
stand that each impact of the foot on the ground will bo 
represented by the elevated part of the corresponding curve. 

In fact, the pressure of the foot on the ground compresses the, 
india-rubber sole and diminishes the capacity of the included 
air-chamber. A part of the contained air escapes by the con- 
necting tube, and passes into the registering drum. 

\Ve see in 11^-. '_'<) that the pressure of the riijit foot, for 
in-tance, commences at the moment when that of the left 
In -ins to decrease; and that in all the tracings then- is an 
;.l.ei -nation between the impads of the t\vo feet. The period 
< f Mi/i/mrt of each foot is shown by a horizontal line which 
joins the minima, of two successive curves. 

The impacts of the ri^ht and left feet have the same dura- 
tion, so that the \\eijjit of the lody passes alternately from 
one foot to the other. It Would not be the same \\itll respect 
to a lame person ; lamenrss corresponds essentially with the 
inequality of the impacts of the two feet. 

Then- is a 1 \\ays a very short period during which the body 

i- partially supported by our foot, but \\hen it already lic- 

!i- jest on the cilhcr thi. time is .sraicely ipial to the 

WALKING}. 115 

sixlli prrt cf tlic dura! ion of a single impact or pressure of 
the loot. 

Intensity of the pressure of the foot upon tlie ground. The 
curves traced by walking 1 may also furnish the measure of the 
effort exerted by the foot upon the ground. The experimental 
shoes constitute a kind of dynameter of pressure; they com- 
press the drum, less or more, according 1 to the effort they 
exert ; and consequently they transmit to the registering level- 
more or less extensive movements. In order to estimate, 
according to the elevation of the curve, the pressure exerted 
by the foot, we must substitute for the weight of the body a 
certain number of kilogrammes. We see thus that, if the 
weight of the body (75 It ilograi nines, for example) is sufficient 
to raise the lever to the height which it attains at the com- 
mencement of each curve, an additional weight will be required 
to raise it to the maximum elevatiou which it attains towards 
the end of its period of pressure. 

That proves that, in walking, the pressure of the foot on 
the ground is not only equal to the weight of the body which 
the foot has to sustain, but that a greater effort is produced at 
a given moment in order to give the body the movements of 
elevation and progression which we have just been studying. 

According to Mons. Cavlet, this additional effort is not more 
than 20 kilogrammes, even in rapid walking, but it is much 
greater in running and leaping. 

Reactions. We shall designate by this name the movements 
\\hich the action of the leg produces on the mass of the body. 
These movements are very complex ; they are effected at the 
same time in every direction, and give to the trajectory 
which a point of the body describes in space, some very com- 
plicated sinuosities. The graphic method alone can enable 
us, at least as yet, to appreciate the real nature of these 

In the first place, what point of the body shall we choose 
in order to observe the displacement caused by the act of 
walking? Almost all authors have taken for this purpose the 
centre of gravity, the point which Borelli places inter nates ct 
pulim. But if we reflect that the centre of gravity changes 
as soon as the body moves, that in the flexion of the legs this 



centre rises, tliat it is altered if we raise our arms, that, in 
fart, it des< rilies within the interior of the body all sorts of 
movements, as Mum as we cease to be motionless, it is easy 
to understand that it will bu impossible to refer to this 
ideal and iimvalilc point, the reactionary movements produced 
liv the pres-ure of tlie feet upon tiie ground. It will be 
belter to chouse a detenu inate ]iart of the trunk of the body, 
the pubis. for example, in order to study its movements in the 
at ualkiug. 

I'll.. Jl. Tr;uisiui*Mi>li "f ;iu c'si-ilhunrv niiiYi/im-ut tnllic registering :i]>|>ur:itu.:. 

The instrument which we have already employed will be 
applicable to tlie study of these displacements'. 

Let there be t\vo Jeri-r drtn/ix, united l>y a long tube T T T. 
Let a vertical osrillary moveiiu nt l>e <;iv(>n to one of these 
levels, so as, for example, to carry the lever L downwards 
into the position indicated by the dotted line, the ether lever 
will be displaced in the opposite direction, and will assume the 
position also shown by the dotted line near it. Under these 
conditions the lowering of one lever corresponds with the ele- 
vation i.f the other, since the compression of the air in one of 
the drums must lead to its expansion in the other. If we 
wish to obtain from the t\\o parts of the apparatus indications 
in the same direction, it would be necessary to turn one of 
the drums. 80 R8 to pl.-ice its lever downwards. 

I , i ti,, if iiKi-Uliidniin ,,f tin- /in, 1 1/ Let us sup] lose that one of 
these levers traces ;i curve on the r-'eistering apparatus, while 
the o'hcr rests, l'\ its point, on tlie pibi> of a 111:111 who is 



walking ; all the vertical oscillations of the pubis will be 


But, in order that the experimental lever may receive and 
transmit faithfully the vertical oscillations which the pubis 
executes during the act of walking, the drum itself must be 
protected from these oscillations. For this purpose an instru- 
ment has been invented, composed of two horizontal arms, 
which turn on a centre. These arms can move only in a hori- 
zontal plane, situated at the height of the pubis of the person 
under experiment ; to one of these arms is fixed the experi- 
mental lever drum. 

Fie. 22. The upper curves, one in full line, the other do' tod, repiei-eut 
the phases of the iinpact and of the rise of the 7ight and left foot. Reading 
the figure from leftt right, ea--h risen)' the curve denotes thecommence- 
ment of pressure: tbe upper horizontal part corresponds with the dura- 
tion of the pressure, and the descent with the rise of the foot. The 
lower horizontal part of the curve indioa'es that the corresponding foot 
is in the air. (> Pv. Oscillations of the pubis from above downwards, 
that is vertically, O Ph. Oscillations in a lateral direction, or hori- 
zontally. It is evident that two oscillations in the vertical direction 
correspond with a single horizontal oscillation. 

The person who walks, follows during this time a circular 
path, pushing before him the arm of the instrument, to which 
is fixed the apparatus which is to experiment on the vertical 
oscillations of the pubis. We get thus the tracing repre- 


sontcd by llio line O P0 (fig. 22). It is seen that the pubis 
rises at the middle of the pressuic exerted by each foot, and 
sinlcs at the instant when the weight of the body passes from 
one foot to the other. 

The real amplitude of those oscillations is about 14 milli- 
metres, according to MOJIS. Carle t. This movement, however, 
varies with the length of the step; it increases with it, but 
this increase docs not depend on the maxima of the curve 
being more elevated, luit on its minima being lower. 

AVe may explain these phenomena very easily. When the 
body is about to quit the support of one leg, this limb is in 
an inclined position, and the result of its obliquity is that its 
superior extremity which sustains the trunk is at a less height. 
The other leg, which reaches the ground at this instant, is 
slightly bent ; it will soon draw itself up, and thus raise the 
body which is supported by it; but in this movement, the 
leg describes the arc of a circle around the foot resting on the 
ground; therefore, in the series of successive positions which 
it occupies, the body rises more and more as the leg which 
supports it approaches the vertical position; it sinks again as 
the ley becomes oblique. 

We can easily peiceive that the length of the step lowers 
the trunk, by increasing the obliquity of the legs. Indeed, 
the constant character found in the maxima of the vertical 
oscillations is explained by this fact, that the leg, when ex- 
tended and vertical, constilules necessarily a constant height 
that, which answers to the maximum of the elevation of the 

Horizontal oscilltilioni of tlte body. The pubis, since that is 
the point whose displacement we are now studying, is carried 
alternately Irom left to right, and from right to left, at the 
same time as it moves vertically. In order to register these 
movements, we make use of a lever-drum arranged in such a 
manner that the membrane is forced inwards and outwards 
alternately by the lateral movements which are given to the 
lever. During this time the registering lever, connected with 
it by means nf tin; tube, oscillates vertically, in which direc- 
tion alone tracings e,m he made on the cylinder. If, in the 
curve which is traced, the elevation corresponds with a trans- 


ference of the pubis towards the right, the depression will 
express a deviation of this poiut towards the left. 

The experiment gives the curve O P It (fig. 22) for the 
tracing of the horizontal oscillations. It is first to be ob- 
served that the number of these oscillations is only half that 
of those which take place in the vertical direction ; so that 
the body is carried towards the right side at the moment of 
the maximum of elevation, which corresponds witli the middle 
of the pressure on the right foot, and towards the left at the 
middle of the pressure on the left foot. This lateral sway- 
ing of the trunk is the consequence of the alternate passage 
of the body into a position sensibly vertical over each foot. 

If we would give an idea of the true trajectory of the pubis 
under the influence of these two orders of oscillations com- 
bined \\ith forward movement, we must construct a solid 
figure. With an iron wire bent in different directions, we 
may illustrate very clearly this trajectory. Fig. 23 is intended 
to represent the perspective view of this twisted iron wire ; 
but we can scarcely expect the reader to comprehend clearly 
this mode of representation. 

Fie. 2.T. Attempt to illustrate, Viy means of n, metallic wire, the sinnons 
trajectory passed through by the pubis. To understand the sketch of 
this solid t gnre, \ve must supp e the wire to ho close to the observer 
at its left hand extremity, while it is removed from him at the riirlit ex- 
tremity. The amplitude of the oscillations has been g.-catly exaggerated 
to render them more intelligible. 

In short, according to the formula of Mous. Carlet, the 
trajectory of the pubis may be inscribed in a hollow half- 
cylinder, with its concave portion upwards, at the base of 



which lie tin- minima, and on the sides of which, the maxima 
t 'rininati 1 tangentiully. 

i'uncnnt jimi/nx* f (//>' Imilif It is clear that during the 
art of valkin^r, tlie body never ceases to advance; but the 
forward movement has not always the same velocity. To 
appreciate these alternate phases of acceleration and retarda- 
tion, it is iieressarv to employ a method which would ^-ive the 
measurement of the space passed thnugli during each of the 

Fio. 24.- S)i"win^ t\vii snro-;sivr |inMtii>ii> ,,t' tin- :inu nf the iii-t 

anil t h<--<- nv.Nj liii^|.-i;i t r i.-in-.' ) i> nt - of t In- K-VI-I > 1'liu 

arm i if th" li'vrr ln'in^ tlirr. rnetma in I. ii Mli, ,IM<| tin- r.i.lius nf the 
c\lililrr In-ill^' nnly six CentimotrOR, a s : niilir :m;nil;ir ilisjilaciMin'ii' nf 
the p'T-mi walking, an-l Hi tin 1 >tyli' *vlii -li wi\tj>, will I'linvsiH":! 1 witii 

sli.ll'c-i wllirll Will In- tn i-in-li ul MI a.s "ill tO 1. 

movements in the act of walking, and which would also 
e\pn the time employed in passing through each of these 
NpUCas. In older to olitain this doiilde indication, we have 
recourse to the following method : 

It i> necessary, lir-t, to ascertain how far tin- body advances 
at tin- dilfeiviit instants of the act of walking. This measure 
of the spaces pa^-rd through, is obtained bv inscribing tlio 
curves of locomotion, no longer on a cvlinder turning with a 
Imt on an immovable our. on which the 


registering levers are displaced by a quantity proportionate to 
the space passed through. 

For this purpose the cylinder is placed on the axis round 
which the instrument turns, and on the central end of one of 
these revolving arms the registering instruments are fixed. 
The ratio of the radius of the cylinder to that of the circle 
described by the person walking, allows us to estimate in the 
tracings the length of the space passed through at each instant. 
This ratio was 50 to 1 in our experiments. 

Thus, in the tracing obtained, if from one point to another 
we reckon an interval of a centimetre, this corresponds \vith 
50 centimetres passed over on the ground by the person 
\\alking. This first notion would be but slightly interesting 
in itself, since it would teach us nothing more than what we 
learn concerning the intervals between two positions of the 
feet, as measured on the ground. The impressions left by 
our steps on soft ground would furnish in a very simple' 
manner this measurement. But if, in addition to this know- 
ledge of the space traversed, the tracing gives us the intima- 
tion of the time passed in traversing it, we are provided 
witli a method of estimating the rapidity of the advance of the 
body at every instant. 

FIG. 25. D Tracing of the impact and rise of the right foot, furnished by 
a le> er subjected at the KIMIC time to 10 viliratimis per second. It is 
seen that the vibrations occupy more space at the end of the pressure 
of the; this expiessus the greatest rapidity of the advance of the 
body at this moment. The same sicctler ition is observed at the end of 
the perod of support o f the right font ; this is explained by the action 
of the left foot, which is, at th s m 'ineiit, at the end of its pressure. 

Fig. 25 shows (line D) the tracings of the impact and rise 
of a limb, and those of the vibrations of a chronograph 
inscribed simultaneously. To obtain these tracings, we cause 
to converge at the same time, on the same lever-drum, two 
transmitting tubes, one of which conveys the variations of 


t'> which the experimental shoe is subjected ifi^. 19), 
and th<- other, ten vihratinns per second furnished by u c-hrouo- 

tuning-fork of lar^e .-i/e. 

| \ tmiiii- f> !!: wli.i^i- viliritii'li" :iro reduced l.y IMM.-.SI-S (if 

, i aata ,, n n, ng lever drum, l.y ..n i-\i <-n 

inditiil ilriini all:i li.-.l t" "ii.- "f il~ iirain-ln-^ Thi- . vr:it tin- 

) liy .-i till \\ itli l\vn In Hi' lii'S tin 1 intlui ni-i- K'th ..I tin.' iinii.wt 

:ind ritiogoftha l"' ! li.-- I- ' n who walks. 

l-'iiT. 'JO shows how the.-e insiniinents are arranged. It is 
seen tliat the drum \\ill l>e allected liy the doul.le inlliieiice 


of the changes in <lie pressure of the foot on the ground, and 
of the vibrations of the tuning-fork ; and this produces in a 
single tracing the interference <>f two movements, giving at 
the same time the notion of the sp-ice traversed, and that of 
the time employed in passing over it. 

In order to analyse this tracing, lot us consider only, in the 
first place, the sinuous curve which obeys at the same time 
the tuuing-fork, and the experimental shoo on the right foot; 
and in this curve let us only examine the elevated part that 
which corresponds with the pressure of the foot upon the 
ground. We see that, during the duration of this pressure, 
the style has passed through a space on the cylinder measuring 
about 2 centimetres ; therefore, as the displacement of the style 
is fifty times less than that of the person walking, lie will have 
advanced about one metre during the pressure of one foot. But 
while he traversed this metre, he did not advance with an 
uniform velocity; in fact, during the first half of this distance, 
the tuning fork made about four vibrations, whilst in the 
second, it has scarcely made two and a half. Thus the foot 
which presses the ground with a force increasing from the 
commencement to the end of its impact, gives the body an 
impulse whose velocity equally increases. 

During the rise of the foot, the line traced by the tuning- 
fork indicates also that the body of the person walking 
progresses with an accelerated motion. That is easily under- 
stood if we remember that, in walking, the rise of one foot 
corresponds exactly with the tread of the other. It is, there- 
fore, the impact of the left foot on the ground which gives the 
body of the walking person an accelerated motion, which is 
observed during the rise of the right foot. 

This method appears to us applicable to all cases in which 
it is necessary to measure the relative durations of different 
phases of movement. 

The inequality in the speed of the man who walks brings 
with it an important consequence. When a man drags a 
load, the effort which he makes cannot be constant ; at each 
foot-fall a redoubled energy is produced in the traction that is 
developed, and as this increase of effort has but a very short 
duration, a series of shocks, as \ve may call them, occurs at 


each instant. T5ut we know tliat these shocks are very un- 
favourable, to the full utilization of mechanical force; we have 
explained (page 49) the inconvenience which would arise 
from them in the work of living motive agents, and the 
manner in which these shocks are lessened by the elasticity 
of muscular fibre. 

Under the conditions in which a man dragging a load is 
placed, if he is attached by a rigid strap to the mass which 
lie has to draw, the shocks of which we have spoken will be 
produced, and he will feel their reaction on his shoulders. In 
order to avoid these painful jerks, and to utilize more fully 
the effort which he makes, we have placed between the car- 
riage and the traction strap an intermediate elastic portion, 
the effect of which has answered our expectations. 

We are endeavouring to construct analogous contrivances, 
which may be adapted to the traces of ordinary carriages, so 
as to lessen the violence of the pressure on the collar, and to 
utilize more fully the strength of the horse. 



Description of the apparatus for the purpose of studying the various modes 
of progression used l>y man Portable registering apparatus Experi- 
mental apparatus for vertical reactions Walking Running Gallop 
Leaping on two feet and hopping on one Notation of these various 
methods Definition of a puce in any of these kinds of locomotion 
Synthetic reproduction of the various modes of progression. 

TIIK principal modes of progression employed by animals, 
are H-iilkiiKj, which we have already described at some length 
as far as it relates to man, rwniiinj at different rates of speed, 
t lie ijallop, and lett^iug on one or two feet. 

The act of walking varies at cording to the nature or the 
slope of the ground; \ve shall have to treit of these dill'erei.t 


in this new study it is no longer p ibbible to employ the 


apparatus which we have used in our previous researches. 
The circular and horizontal track on which the experimenter 
was obliged to walk must be exchanged for surfaces of every 
kind and of every slope. 

If the new instruments to which we must have recourse 
leave the experimenter more liberty in his movements, they 
ai'e, on the other hand, relatively less complete as to the indi- 
cations which they furnish ; therefore, we can only require 
from them two kinds of indications ; those of the pressures of 
the feet on the ground, and those of the vertical re-actions 
which are communicated to the body by these pressures. 

Fig. 27 shows a runner furnished with apparatus of the 
new construction. He wears the experimental shoes which 
we have already described, and holds in Ids hand a portable 
registering instrument, on which are traced the curves produced 
bj r the pressure of his fret. As the cylinder of this instru- 
ment turns uniformly, the curves will be registered in propor- 
tion to the time, and not to the space traversed during 1 each 
of the acts by which this curve is traced. 

In order to facilitate the experiment, and to allow the 
apparatus to assume a uniform motion before it traces on the 
paper, we have recourse to a special expedient. The points 
of the tracing levers do not touch the cylinder; but in order 
to bring tlnm in contact witli the paper, an india-rubber ball 
must be compressed. As soon as this compression ceases, the 
points retreat from the c}'linder, and the tracing is no longer 
produced. In fig. 27 the runner holds this ball in his left 
hand, and compresses it with his thumb. 

In addition to this, the runner, in order to obtain Ihe 
tracings of the vertical re-actions, carries on his head an 
instrument whose arrangement is represented in fig. 28. 

It is an experimental lever-drum fixed on a piece of wood, 
which is fastened with moulding wax on the head of the ex- 
perimenter, as seen in fig. 27. The drum is provided with 
a piece of lead placed at the extremity of its lever ; this mass 
acts by its inertia. 

While the body oscillates vertically, the mass of lead resists 
these movements, and causes the membrane of the drum to 
sink when the body rises, and to rise when the body descends. 



I ,,. 27. Uuuiiur provided wiili tli<- :i]'iunitus i.itci:Jcd to register his 


From alternate actions a current of air results, which, 
transmitted by a tube to a registering lever, shows by a curve 
the oscillatory movements of the body. 

Fin. 28 Instrument to register the vertical re-actions during the various jiticus. 

We will not enter into the details of the experiments which 
have served to verify the exactitude of the tracings thus 
obtained; they consisted in adjusting the weight of the disc 
of lead and the elasticity of the membrane of the drum, 
until the movements given to the apparatus are faithfully 
represented in the tracing. 

We will call step-curves each of the curves formed by the 
pressure of a foot upon the ground, and we will designate by 
the name of ascending or descending oscillations, the curve of 
the vertical re-actions on the body. 

1. Of walking. We have already pointed out the distinc- 
tive character of walking considered as one of the modes of 
progression in man. We have said that the body, in walking, 
never leaves the ground, and that the footsteps follow each 
other without any interval, so that the weight of the body 
passes alternately from one foot to the other. 

But this definition cannot apply to walking on an inclined 
surface, on yielding soil, or upstairs. Being obliged to pass 
rapidly over these peculiar conditions of walking, we will only 
give the tracing which corresponds with the act of mounting 
a staircase (fig. 29). 

It is to be remarked that the step-curves encroach on each 
other, showing, that each foot is still pressing on the ground, 
when the other has already planted itself on. the next step. 
Besides this, it is at the time of this double pressure that 
the losver foot exerts its maximum force ; it is at this moment, 
in fact, that the work is produced which raises the body to 
the whole height of a step. 



Nothing like lliis is observed in the descent of a staircase; 
tin- step-curves cease to encroach 0:1 c.icli other, and succeed 
each other very nearly as in ordinary \\alking on level 

l'i .;. '?'.' Tracing prodnee'l l>y walking upstairs. TX tr.-viii<_r <>f tin- pressure 
aii'l i ise cif tin- rijlit fii it full line. (',. tracing ul the li-ft I'm it (tintf-il 

lilie). It is sccll that flu- l/U I VI- x )iv,.,lueeil l.y lln- t'i'i-t i -1 1, T, -aril i 'Hi' 'll 11 10 

<> her. Mini tliat tin- in.-ixiiii.i of the pressures of the fuct curru.spiinil with 

till- UlH-1 lift lit, 1 IH' 

2. Of running. Tins mode of progression, more rapid 
than walking, consists, like if, in alternate treads of the two 
feet, wli< >se step-curves follow eacli other at equal iiu.Tvals; 
but it presents this diil'erence, that in running;, the body 
leaves the ground for an instant at each step. 

Accordingly, as r:muing is more or less rapid, different 
names are <jiv"ii to it; those of the t/i/iiiiiustic nunrh and the 
trot present no utility in a physiological point of view ; they 
correspond, with but slight variations, to running at various 
degrees of speed. To ascertain the principal characters of 
this mode of progression, it is only necessary to analyse 
fig. 30. 

I 10 " l-.i iiu- produced by runn '07 (in ni.-in) |l (eurve fm-nii-il 1>\ :i 
I'M II line , i 111 1 1. let an I n~e of ri/ht to it. li. , I tie. I 1 in -i ae 1 1 "ii ,i| the left i> oscillations and vertical re actions of tneli.l\. 

The Jiressure.S of the |',-i-t ;ii-,. niol'e energetic than ill 

w. ilking; in fact, they not only sustain the \\eight of the 


body, but impel it with a certain speed both upwards and 
forwards. It is known that to give a mass a rising motion, 
a greater effort must be exerted than would be sufficient 
simply to sustain it. 

The duration of the pressures on the ground is less than in 
walking ; this brevity is proportional to the energy witli 
which the feot, tread on the ground. These two elements, 
force and brevity of pressure, increase generally with the 
speed at which a person runs. The frequency of the foot- 
falls increases also with the epeed of the runner ; but among 
the various kinds of running, there are some in which the 
extent of space passed over in a given time depends rather 
on the extent of each pace than on their number. 

The essential character of running is, as we have said, the 
time of suspension during which the body remains in the air 
between two foot-falls. Fig. 30 clearly shows the suspension, by 
the interval which separates the descent of the curves of the 
right foot from the ascent of the curves of the left foot, and 
vice versa. The duration of this time of suspension seems to 
vary but little in an absolute manner ; but if we compare it 
with the speed of a runner, we see that the relative time 
occupied by tnis suspension increases with the speed of the 
course, for the duration of each tread diminishes in proportion 
to this speed. 

How is this suspension of the body at each impulse of the 
feet produced ? We might think, on first consideration, that 
it is the effect of a kind of leap, in which the body is pro- 
jected upwards in so violent a manner by the impulse of the 
feet, that it would describe in the air a curve, in the midst of 
which it would attain its maximum elevation from the ground. 
In order to convince ourselves that such is not the case, let us 
make use of the apparatus which registers the re-actions or 
vertical oscillations of the body. 

In fig. 30 is seen (upper line 0) the tracing of oscillations 
in running. This trace shows us that the body executes each 
of its vertical elevations daring the downward pressure of the 
foot, so that it begins to rise as soon as the foot touches the 
ground ; it attains its maximum elevation at the middle of the 
pressure of this foot, and begins to descend again, in order to 


roach its minimum, at the moment when one foot has just 
risen, and l>"fore the other has reached the ground. 

This relation of the vertical oscillations to the pressure 
of the feet shows plainly that the time of suspension does not 
depend on the fact that the body, projected into the air, has 
loft the ground, but that the leys lutre wit ltd ni ten from the 
ground by the effect of their flexion; and this takes place at 
the very moment when the body was at its greatest elevation. 

We shall have again to recur to these phenomena when we 
come to speak of the paces of the horse, in which a similar 
suspension of the body exists, aoid which are called on that 
account elevated paces. 

The influence of the different inclinations of the ground 
acts in nearly the same manner in running as in walking, 
with this difference, that in running, their effects are generally 

3. Of the gallop. In the modes of progression described 
hitherto, the movement of the limbs is regularh' alternate, so 
that the succession of stops is made at equal intervals. 
These are the normal hinds of human locomotion ; but man 
can imit.iie, to a certain extent, by the movements of his feet, 
those periodically irregular cadences \\fiich axe produced by a 
horse- when he gallops Children, in their amusements, often 
imitate this mo-le of locomotion, when they play at horses. 
This abnormal kind of motion is of no interest, except to 
explain the mechanism of the gallop in quadrupeds. 

Bv registering together the step-curves and the re-aclion*, 
it is seen (fig. 31) that the foot placed behind is the first 
which readies the ground; that it exerts an energetic and 
prolonged pressure, towards the end of which the foot iu front 
touches the ground in its turn, but during a shorter time ; 
after which there is a considerable period of suspension. 
Thus, (here is a moment when the two feet are in the air. 

In this mode of progression, the re-actions are similar in 
elm-actor, in some respects, to the pressures. In fact, a long 
re-acti.>n (line O) is produced, in which wo recognise the 
interfere^ i- () f two vertical osi -illations, the second of which 
commences before the first has finished. After this re-action 
o is observed a lowering of the curve, whose minimum 


corresponds with the moment when the two feet are in 
the air. 

FIG. 31. Man galloping wilh the right foot first. Step-curves and re- 
actions. There is an encroachment of one curve over the other, and thun 
a snspi nsion of the body. The curve O, which corresponds with the 
re-actions, snows the effect of the two successive impulses exerted on 
the body by the feet. 

4. Of leaping. Although leaping is not a sustained mode 
of progression in human locomotion, we will say a few words 
about it, in order to complete the series of the movements 
which man is able to execute. 

The two feet being joined together, we can make a series 
of leaps, and advance thus, by imitating the mode of locomo- 
tion of some birds, or of certain quadrupeds, as the kangaroo. 

FIG. 32. Leap on two feet at once, D and G. The line R, the curve of re- 
actions, shows that the maximum of elevations corresponds with the 
middle ol the pressure of the feet. 

The apparatus intended to illustrate the vertical oscillations 
of the body, being placed on the head of the experimenter, 


we get tliroo tracings at once ; those of the pressures of the two 
feet, ami that of the re-actions ; these furnish fig. 32. 

We sec here that the maxima of the curve of re-actions 
(line R) coincide with the pressures. Thus, ly their united 
energy, tlie t\v> legs raise the body, and then let it fall again at 
tlie moment \vlien they bend and prepare to act afresh. 

Hopping n one foot gives the tracings (fig. 33) which 
only consist in the pressure and rise of a single foot. The 
elevations of the liody coincide with tlie step-curves In fact, 
when the speed of the leap is lessened, it is prolonged more 
especially at the period of the pressure of the foot on the 
ground, that of suspension remaining very nearly constant. 

Fio 33. D, series of hup* on the right foot. The duration of the time 
of Mi*|H'ii.siiiii remains evidently OOILataut, even when tliutot'the pressure 
of the loot varies. 

In certain species of animals, successive leaps constitute 
the ordinary mode of locomotion ; it will be interesting to 
study by the graphic method the various paces of these 


Among tlie characters of various modes of progression, it 
is the rhythm of the impact of the feet which is the most 
striking. The strokes of the feet upon the ground give rise 
to sounds, the order of whose succession is sufficient for a per- 
son with an ear accustomed to them to recognise the kind of 
pace which originates them. Wo will, therefore, endeavour 
to establish the classification of the various paces by attending 
to this order of succession. 

In order to give the figure of each of these rhythms, we shall 
employ the musical notation, modified so as to furnish at the 


same time the notion of the duration of each pressure, that of 
the foot to which this pressure belongs, and also the length of 
time during which the body is suspended. This notation of 
rhythms is constructed in a very simple manner from the 
tracings furnished by the apparatus. 

FIG. 34. 

Let us return (fig. 34) to the curve which corresponds witli 
the act of running in man. Below this figure let us draw 
two horizontal Hues 1 and 2 ; these will form the staff on 
which will be written this simple music, consisting only of 
two notes, which we shall call right foot, left foot. From the 
commencement of the ascending part of one step-curve be- 
longing to the right foot, let us let fall upon the staff a per- 
pendicular (a) ; this line will determine the commencement of 
the pressure of the right foot. A perpendicular (') let full 
from the end of the curve will determine where the pressure 
of this foot ends. Between these two points, let us trace a 
broad white line ; it will expi-ess, by its length, the duration, 
of the pressure of the right foot. 

A similar construction made on the step-curve (No. 1) will 
give the notation of the pressure of the left foot. The nota- 
tions of the left foot have been shaded with oblique lines to 
avoid all confusion. 

Between the pressure of the two feet there is found to "be silence 
in the rhythm ; that is to say, the expression of that instant 
of the course when the body is suspended above the ground. 


If we note in this manner the rhythms of all the juices used 
by man, \ve shall ohtain a synoptical table which will much 
facilitate tin- coiiipan.-ou of these varied rhythms. Fig-. 25 
represents the syin>j>ti<-nl ni>t<iti<m of the four kinds of progres- 
sion, or paces, which are regularly rhythmical, and in which 
the two feet act alternately. 

Line 1 represents the nutation <>j the rhythm of the ivalkin-j 
/"i'. This is the principle of the representation. 

The pressure of the right foot on the ground is represented 
by a thick white stroke, a sort of rectangle, the length of 
which corresponds with the duration of that pressure. For 
the left foot there is a greyish rectangle shaded with oblique 

These alternations of grey and white express, by their suc- 
cession, that in walking the pressure of one foot succeed^ the 
other without allowing any interval between the two. 

Fio. 35. Synoptical notation of the four kinds of progression used by num. 

Lino 2 is the notation which corresponds with the ascent <>f 
it staircase. It is seen, agreeably with what has been already 
explained (fig. 29), that the step-curves encroach on each 
other, and that, consequently, the body during an instant rests 
on b:>th leet at Once. 

Line ;; corresponds with the rhythm f runniiii/. After a 
fihorter step-curve of the right foot than in the walking pace, 
an interval is teen which corresponds with the suspension of 
the body; then a short impulse of the left foot, followed by a 
fresh suspension, and so on continually. 

Line 1 answers to a more ni/ii,l nil,' <//' niiiiiin;/. AVe find in 
it a shorter duration of the pressures, a longer time of the 


suspension of the body, and a more rapid succession of the 
various movements 

FIG. 36. Notations of the gallop. 1. Left gallop. 2. Right gallop. 

Fig. 36 is the notation of the gallop of children, a mode of 
progression in which both the feet do not move in the same 
mauuer. In this figure, Hue 1 represents the left gallop that 
is, with the left foot always forward. It is seen that the right 
foot presses on the ground first; then the left falls and touches 
the ground for a shorter time. 

Then, there occurs a suspension of the body, after which 
the right foot falls afresh, and so on. The time of the simul- 
taneous pressure of both feet is measured according to the 
space by which the shaded rectangle rests on the white one. 

Line 2 is the notation of the ri/jht gallop ; that is to say, 
when the right foot is always in advance, reaching the ground 
later than the left. Thus, in the gallop, the body is sometimes 
in the air, sometimes on one foot, and sometimes supported 
by two. 

Finally, the notations represented in fig. 37 would be: 
upper line, a series of jumps on two feet ; lower line, a series 
of hops on the right foot only. 

Fio. 37. (Upper line), notation of a series of jumps on two feet. (Lower 
line), nota'ion of hops on light foot. It is seen that there is constancy 
in the durations of suspension, notwithstanding the variability of the 

Thk method of representation is less complete than the 


curves given before, for it does not indicate the phases of 
variable pressure exerted by the foot upon the ground ; but it 
is much more simple, and allows the two modes of progression 
to be compared much more easily than the other. It will be 
seen farther on, when speaking of quadrupedal locomotion, 
that the complication of the subject renders it indispensable 
to employ this very simple notation of the rhythm of move- 

Definition of a pace in any kind of progression. It is usually 
considered that a pace is produced by the series of movements 
which are executed between the action of one foot and that 
of the other, whether we choose for the commencement of 
the pace the instant that the feet reach the ground, or that 
when they rise from it. Thus, in measuring a pace on the 
ground, we usually take as its length the distance which 
separates one portion of the print of the right foot from 
a similar point of the impression made by the left. 

We shall be obliged to depart from this usage. Although 
we regret any innovation, yet we shall consider the standard 
pace only as half a pace, and we shall thus define it : A pace 
is the series of movements executed between two similar positions of 
the same foot between the two successive treads of the right 
foot, for example, or two successive elevations of the left 
foot, &c. 

In the same manner the extent of a pace on the ground 
will be the distance which separates two homologous points 
taken in the two successive impressions of the same foot. 
The pace is estimated in this manner in Mexico. This is the 
only method of counting which will prevent errors in the very 
complicated moments of quadrupedal progression. 



Since wo have completed the analysis of a phenomenon of 
which we now seem to understand all the details, it is by 
synthesis that we will endeavour to construct a counter-proof. 
This method has proved very useful in verifying our theories 
concerning certain physiological actions, as, for instance, the 
circulation of the blood. It consisted in representing, by arti- 


ficial means, the movements and the sounds of the heart, Ilio 
arterial pulsations, &c., and we thus proved the correctness 
of our theories as to the nature of these phenomena. The 
same method will serve hereafter to verify our theories of the 
flight of insects and birds. In the present case it is necessary 
to represent, according- to the data afforded by analysis, the 
movements of walking and of the other paces employed by 

Every one knows Ilie ingenious optical instrument invented 
by Plateau, and called by him " Phcnakistoscope." This 
instrument, which is also known by the name of Zootropo, 
presents to the eye a series of successive images of persons or 
animals represented in various attitudes. When these atti- 
tudes are co-ordinated so as to bring before the eye all the 
phases of a movement, the illusion is complete ; we seem to 
see living persons moving in different ways. 

This instrument, usually constructed for the amusement of 
children, generally represents grotesque or' fantastic figures 
moving in a ridiculous manner. But it has occurred to us 
that, by depicting on the apparatus figures constructed with 
care, and representing faithfully the successive attitudes of the 
body during walking, running, &c., we might reproduce the 
appearance of the different kinds of progression employed 
by man. 

MOMS. Carlet, whose remarkable studies of walking we have 
before quoted, and Mons. Mathias Duval, professor of anatomy 
at the Eeole des Beaux-arts, have carried out this plan, and, 
after many attempts, have arrived at excellent results. 

Mous. Duval is engaged in perfecting his diagram, which 
furnishes to the eye sixteen successive positions for each kind 
of locomotion employed by man. Each figure is carefully 
drawn according to the results afforded by the graphic method. 
When rotated with suitable speed, the instrument shows, with 
perfect precision, the different movements of walking or run- 
ning. But its principal advantage is that, by turning it less 
quickly, we cause it to represent the movements much more 
slowly, so that the eye can ascertain with the greatest facility 
these actions, the succession of which cannot be apprehended in 
ordinary walking. 




[nsnfficiency of the senses for the analysis of tlic paces of the horse 
Comparison of I Midi's Khytlmis of tlie prices studied by means of the 
car Insufficiency of language to express th"sc rhythms -Musical 
nutation Notation of the amble, of the walkinj pace, of tlie trot 
Synoptical table of paces noted according to the definition of eacli of 
them by dilferent authors Instruments intended .to determine by tlie 
graphic method the rhythms of the various paces, aud tho re-actions 
which accompany them 

THERE is scarcely any branch of animal mechanics which 
has given rise to more labour and greater controversy than the 
question of tho paces of the horse. Tlie subject is one of 
grent importance to a large number of persons engaged iu 
special pursuits, but its extreme complexity has caused in- 
terminable discussions. Any one who proposed at the present 
time to write a treatise on the paces of the horse, would have 
to discuss many different opinions put forward by a great 
number of authors. 

While reading these works, on which so much sagacity of 
observation and such rigorous reasoning have been expended, 
one is astonished to find that the greater number of these 
writers are not agreed in their definitions of the paces. This 
disagreement in similar observers can only be accounted for 
on the principle of the insufficiency of tho means at their 
disposal to enable them to analyse tlie very complex and rapid 
movements of the horse. The dilliciilty of expressing in 
words the rhythms and tl.o durations of these various move- 
ments adds still more to the confusion. "When a horse is 
running, and passing from one kind of motion to another; 
when he moves his limbs \\ith a rapidity which makes one 
di/x.v, and according to the most varied rhythms, how can we 
appreciate and deserve, faithfully all these actions? It would 
be as e.isy u task, after looking ut the fingers of a pianist 


when running over tlie keys, to try and describe the move- 
ments which have just been executed. 

Still, in the midst of this confusion, it has been found 
possible, by observation alone, to establish certain divisions 
which singularly simplify the study. Thus, certain paces give 
to the ear a rhythm in which the strokes <.f the hoofs succeed 
each other at sufficiently regular intervals; others, such as the 
different kinds of gallop, offer an irregular rhythm, recurring 
at periodical times. These latter paces are the most difficult 
to analyse. 

But if we observe a horse either at a walking pace, ambling, 
or trotting, and if we concentrate our attention on the anterior 
limbs alone, or on the posterior ones, we perceive that the 
rhythm of the impacts and elevations of the right and left 
foot entirely resemble those of the feet of a man walking or 
running- more or less quickly. The alternation of the strokes 
of the feet is perfectly regular, if the horse be not lame of 
one of the limbs under observation. 

If we then pass to the comparison of the movements in the 
two fore and hind legs on the same side, we see that the two 
feet on the right side, for example, make the same number of 
steps, and that if one of them strikes the ground at a greater 
or less interval before the other, this is preserved as long- as 
the same pace is continued. Add to this that the length of 
the step is the same for both the fore and hind limbs, of 
which fact we may convince ourselves by seeing that these 
two feet always leave on the ground prints situated at the 
same distance from each other. In general, the hind-foot 
covers the print left by the corresponding fore-foot ; if the 
prints be not covered, they preserve always the same distance 
from each other. Thus, the steps of the fore and hind legs 
are of the same number and the same extant ; these facts 
have not escaped former observers. 

Dugcs lias compared the quadruped when walking to two 
men placed one before the other, and following each other. 
According as these two persons (who ought both to take the 
same number of stops) move their limbs simultaneously, or 
alternately; according as the man in front executes his move- 
ments more quickly or more slowly than the one behind, we 


see all the rhythms of the movements which characterise 
the different pairs of the horse reproduced. 

Every one has seen in the circus or the masquerade those 
figures of animals whose legs are formed by those of two mei* 
witli their bodies concealed in that of the horse. This gro- 
texjut; imitation bears a striking resemblance to the animal, 
when the movements of the two men are well co-ordinated, so 
as to reproduce the rhythms of the paces of a real quadruped. 

In the examination of the tracings furnished by the graphic 
method when applied to the paces of the horse, we may have 
recourse to the theory propounded by Duges; we shall then 
find the curves furnished by human locomotion twice repeated. 
We shall see that the difference between one pace and another 
consists in the manner in which the footfalls of the hind leg 
of a horse succeed each other, with relation to those of the 
fore leg on the same side. But this determination of the 
order of the succession of footfalls presents singular dilli- 
culties, even for the most skilful observers. 

Many attempts have been made to bring to perfection the 
means of observation, and to remedy the insufficiency of 
language in the description of the observed phenomena. 
Long since, the rhythm of the steps according to the sounds 
which they produce has been substituted for their examination 
by means of the eye. The ear, in fact, is better adapted than 
the eye to distinguish the rhythms or relations of succession. 
To ascertain the order in which each limb strikes the ground, 
certain experimenters have attached to the legs of the horso 
bells of different tones, which can be easily distinguished from 
each other. 

A point \vhich has been better ascertained with respect to 
the locomotion of the horse, is the determination of the space 
passed over on the ground during each of the various kinds 
of paces. This space has been directly measured by means 
of the distance between the prints of the feet left on the 
ground. To render the distinction between the footprints 
more easy, each of the animal's feet has been shod in a 
iliHiTcnt manner. Besides this, observers have studied the 
proportion which exists between the. height of the animal and 
the length of its various paces. All who have made 


any progress in this interesting; study Lave arrived at it by 
the employment of rigorous methods of observation. 

On the other hand, the manner of expressing the observed 
phenomena has occupied the attention of different authors. 
Almost all have had recourse, with great advantage, to the 
use of drawings, but have agreed but little in their mode of 
representing the successive actions which characterise the 
different paces. The most perfect kind of representation 
is that employed during the last century by Vincent and 
Goiffon.* A sort of musical staff, composed of four lines, 
served to note the instant of each impact of the four feet, and 
the duration of the succeeding pressures on tlie ground. This 
notation resembles, to a certain degree, that which we have 
employed to represent the different rhythms of human loco- 
motion, and which will hereafter serve to explain the various 
paces of the horse. But we must not forget that the method 
of Vincent mid Goiffon only expressed a succession of move- 
ments observed by the sight or the ear, and that it realised no 
greater exactitude than that of the individual observer. 

Our registering instruments resolve the double problem of 
analysing with fidelity the acts which the senses could not 
accurately appreciate, and expressing clearly the result of this 

Before we describe our experiments, we shall, in order that 
the reader may understand their utility, try to present a 
summary of the present state of the science, and to show what 
disagreement exists on various points among different authors. 
As the standard definitions are not always easy to be under- 
stood, we shall add to them the notation of each of the paces, 
trusting that this method of representation will render them 
more intelligible, and especially more easy to be compared 
with each other. 

Notation of the various paces of the horse. Recurring to the 
comparison used by Duges, let us represent the horse as com- 
posed of two bipeds walking one behind the other. We must 
determine the manner in which the rise and fall of the feet 

* Meiuoire artificielle des principes relatifs h la fiddle reprdscntatiou des 
aiiimaux, taut et. peinture qu'en sculpture. Altoid, 17CJ>. 


sun-red each other, in each of the persons supposed to be 

< >t' tin' niiili'i'. Let ns take the simplest case, iii which the 
INNO jiersons walking steadily go through the same movements 
at the same time. If \\ e represent, by the notation before 
employed, the movements of these two men, placing at tho top 
the notation which belongs to the foremost, and below it thai 
of the hindmost, we shall have the following iigure : 

Fio. 38. Notation of a horse's amble. 

The footfalls of the right and left foot being produced at 
the same time by the person walking in front and by him who 
follows, must bo represented by similar signs placed exactly 
over each other. Thus, in the paces of the horse, this 
agreement between the movements of the. fore and hind limbs 
belongs to the amble. The notation (fig. 38) will be that of 
a horse's amble ; the upper line referring to the movements 
of the fore quarters of the animal, and the lower line to the 
hind limbs. 

The standard definition is the following: "The amble is a 
kind of pace characterised by the alternate and exclusive 
action of two lateral l>i/ilx ." Authors are entirely agreed on 
this point. Let us add that in the amide the ear perceives 
onlv tn-ii In-lit^ at each pace, the two limbs on the same side 
striking the ground at the same instant. In the notation 
tln^r u\o sounds are marked by vertical lines joining the two 
synchronous impacts. 

In the ami ile the pressure of tho body on the ground is 
said to be Idtrntl, as the t\vo limbs on one side only are in 
contact with the ground at the same time. 

(if the irdlliinif /i/tci'. -According to the defiailion of the 
greater number of authors, the n;ilkinij ;n/<r consists in an 
eijiial succession of imp ids of the t'.nr feet, which strike the 
ground in the I'olloNxing order: if the right font be considered 
as moving lir>t, \N e shall have the following succession r'ujlit 
fore /""', I'H hind foot, lfftjore-/oot t and then iujht hind-foot. 


To express this succession of movements of the two persons 
walking, it is only necessary to alter the place of the signals of 
the hind feet with respect to those of the fore feet. We shall 
obtain the rhythm indicated by authors by causing the signals 
of the hiiid feet to slip towards the left, which will give the 
following- figure : 

FIG. 39. Notation of the horse's walking pace 

It is seen, therefore, that when compared with the amble, 
the walking pace consists in an anticipation of the hinder 
limbs, whose footfalls precede those of the corresponding fore 
limbs by the half of the duration of one of their pressures 
on the ground. 

If the notations be read from left to right, like ordinary 
writing, it is evident that each sign situated farther to the 
left than another precedes it in order of succession. Thus, 
in fig. 39, the impact of the right hind-foot precedes that of 
the right fore-foot. But as it is of little consequence, in the 
series of successive acts of the same kind of pace, whether we 
choose one instant rather than another as the point of depar- 
ture, we shall always take as the commencement the impact 
of the right fore-foot. 

The ear distinguishes four beats, separated by regular 
intervals, each of which is indicated in the notation by a 
vertical line. Finally, the body rests on the ground twice 
laterally and twice diagonally during one entire pace. It is 
easy to ascertain this by looking at fig. 39, in which, after 
the first impact, the body rests on the right feet (lateral biped 
L) ; after the second impact, on the right foot in front, and 
the left foot behind (diagonal biped D), &c. 

But this notation only expresses the theory of the most 
extended pace. The equality of intervals between the strokes 
of the feet is not admitted by all writers. We ehall see, in 


the course of our experiments, that the walking pace, iu fuct, 
may present different rhythms. 

Of the trot. The notation of the trot is obtained l>y a 
more decided anticipation of the hinder limbs, each of \\hieh 
will have entirely completed its pressure on the ground, 
and begun to rise at the moment when the fore-leg on the 
same side has completed its stroke. Fig. 40 expresses the 
absolute alternation of the two persons supposed to be 

Fia. 40. Notation of a horse's trot 

Authors agree also on this point, that in the trot, the 
limbs which act together are associated in diagonal pairs. 

The ear perceives but tu-o sounds of the hoofs, as in the 
amble, but with this difference, that it is always a right and 
left foot together, and not two feet on the same side, which 
produce each sound. 

The notation also shows that the pressure of the body on the 
ground is always diagonal. What it does not express is, that 
between successive pressures, the body of the animal is, for an 
instant, suspended in the air. This suspension arises from 
the fact the trot is not a walking, but a running pace, and 
that to represent it faithfully we must place together two 
notations similar to that which is represented in fig. 34. 

We have designedly omitted the time of suspension in the 
former notation; it would have rendered a difficult subject 
still more complicated. Besides, this suspension does not 
always take place ; certain horses have a luic trot, which has 
nothing to characterise it except its rhythm in double time 
and the diagonal impacts of the feet. 

We will not fatigue the reader by detailing the definition 
of all the paces admitted by dill'erent authors. We shall 
merely present in a synoptical table the scries of notations 
which c invspoml with them. In this table (lig. 11) it is 
, th it all the U>u; / ;/c< * may be considered as derived 


from the amble, ami that if we wished to make a methodical 
classification, we should group them in a series of which the 
amble would be the first term, and all the other terms would 
be obtained by means of an increasing anticipation of th 
movements of the hinder limbs. Fig. 41 represents this series. 
In the notation of each kind of pace, we have left on the same 
vertical the impact of the right fore-foot, which we shall choose 
as the commencement of each pace, and which will serve aa 
a point of reference to characterise each kind of locomotion. 

This table, prepared from different treatises on the horse, 
represents as faithfully as we have been able to depict it, 
that which each axithor admits as constituting each particular 
kind of pace. The explanatory notes show the disagreement 
which exists bet\veen the various theories relative to the suc- 
cession of movements which characterise each of them. Thus 
Ave see, that with the exception of the amble, on which all 
are agreed, all the other kinds of paces are defined in a 
different manner by various authors. Thus, the notation 
No. 2, which, according to Merche, would correspond with 
the broken amble, would be, according to Bouley, the expres- 
sion of the high step, or the pace of Norman ponies ; while 
this same Norman pace would be, according to Lecoq, that 
which is represented in No. 9. We also see that the notation 
of No. 3 would correspond, according to Merche, witii the 
ordinary step of a pacing horse, while Bouley would consider it 
as a broken amble, and Lecoq the iraquenade which traqiienade, 
according to Merche, would not differ from the pace repre- 
sented by the notation No. 10. The ordinary walking pace 
itself is not understood in the same manner by different 
writers, and if the greater part of them, with Vincent and 
Goiffon, Colin, Bouley, &c., admit in this pace a succession of 
impacts at unequal intervals, it is to be observed that the 
theory of Lecoq and Ilaabe, concerning the normal pace, iy 

This disagreement can easily be explained : first, tl.e 
observation of these movements is very difficult ; then, each 
pace must naturally present, according to the conditions 
under which it is studied, the different forms which each 
writer has arbitrarily taken as the type of the normal walking 



Fio. 41 -Svii..],ti.-;il ii"t.iti'>ns nf tlic paces of the horse, according to 
various writers. Sou Description at the foot uf iiagu H7. 


price. Each one luis suffered himself to be guided in this 
respect by theoretical considerations. Those who admit equal 
intervals between the four footfalls, have thought that they 
found in this type more clearness and a more decided dis- 
tinction between tlte amble and the trot. The other writers 
have attempted the realisation of a certain ideal in the kind 
of pace which served them as a type. For Ka.ibe, it was the 
maximum of stability, which, according- to his theory, ia 
obtained when the weight of the body rests longer on the two 
diagonal feet than on the two lateral feet ; whence arises the 
choice of the type represented by the notation No. 6. Lecoq, 
thinking, on the contrary, that the most rapid pace is the best, 
lias chosen as his type the pace in which the body rests longer on 
the two lateral feet than on the diagonal ones (notation No. 4). 
Whatever may be the value of these considerations, of 
which practical men alone can judge, it seems to us that the 
physiologist must first of all endeavour to search for facts, and 
must take simply such types as experiment may reveal to him. 
It is for this purpose that the investigations have been made with 
registering apparatus, the result of which will now be given. 


For the experimental shoe employed in the experiments made 
on man has been substituted, on the horse, a ball of india- 
rubber filled with horsehair, and attached to the horse's hoof 
by a contrivance Avhich adapts it to the shoe. 

No. \. Amble, according to all writers. 

! iim ''l e > according to Mercho. 

No 2 ! ^ ro ^ CI! iim ''l e > according to Mer 
' ' ( Hi^h step, according to Bouley. 

C Ordinary step of a /incm?/ horse, according to Mazuro. 
No. 3. < Broken amble, according to Buulcy. 

( Traquenade, according to Lecoq. 
No. 4 Normal walking pace, according to Lecoq. 

No. 5. Normal walking pace (Bouley, Vincent and Goiffon, Soil, yscl, Colin). 
No. 6. Normal w ilkint? pace, according to Raibe. 
No. 7. Im-gifar trot (trot deconsu 1 . 

No 8. Ordinary trot. (In thf figure, it is supposed that the aninvd tmts with- 
out leaving the ground, which occurs but rarely. Tliu onlj takes into 
account the rhythm of the impacts of tiie i'cct.) 
No. 9. Norman pace, fnmi Lecoq. 
No. 10. Traquenade, from Merche. 



By turning an adjusting screw we fix it to the horse-shoe 

liy three catches, which 
keep the instrument se- 
curely fastened. A strong 
band of india-rubber passes 
over the apparatus (fig. 42), 
and keeps in its place the 
ball filled with horse-hair, 
so as to allow it to rise 
slightly above the lower 
surface of the hoof. When 
the foot strikes the ground, 
the india-rubber ball is 
compressed, and drives a 
part of the confined air 
into the registering instru- 
ments. When the foot is 
raised, the ball recovers its 
form, and draws again into 
its interior the air which 
(he pressure had expelled. 
These instruments soon 
wear out on the road, but 
will last during some time on the artificial soil of (lie riding-- 

For experiments which we have made on ordinary roads, 
we have had recourse to an instrument represented in fig. 43. 
To the leg of the horse just above the fetlock joint is 
attached a kind of leather bracelet fastened by straps. In front 
of this bracelet, which furnishes a solid point of resistance, 
are pi iced various pieees of apparatus. There is, first, a flat 
box of india-rubber firmly fixed in front of the bracelet ; this 
box communicates, by a transmission tube, with the registering 
apparatus. Kvery pressure exerted on the box moves the 
corresponding registering lever. It is evident that all the 
movements of the horse's foot are shown by pressures on the 
india-rubber box, and are immediately signalled by the regis- 
tt ring levers. 

For this purpose, a plate of copper, inclined about 45, is 

I-'iu. !-. Experiment il :ip|>-ir iti.s lo show 
the pressure of the horse's hoof mi the 



connected at its upper extremity with a kind of hinge, whilst 
its lower end is fastened by a solid wire to the upper face of 
the india-rubber box, on 
which it presses by means 
of a flat disc. On a wire 
parallel to the slip of 
copper slides a ball of lead, 
tlie position of which can 
be varied in order to in- 
crease or diminish the 
pressure which this jointed 
apparatus exerts on the 
india-rubber box. 

The function of this 
apparatus is analogous with 
that of the instrument re- 
presented in fig. 28, in- 
tended to show the re- 
actions which are produced 
in various kinds of loco- 
motion ; only the inclina- 
tion of the oscillating por- 
tions allows them to act on 
the membrane during the 
movement of the elevation, 
the descent, and the hori- 
zontal progress of the foot. 

When the hoof meets 
the ground the ball has a 
tendency to continue its 
motion, and compresses Flfl 43._ Apr ,. ira t us to give the sifrmi- of 

with force the india-rubber tlie pressure and rise ol the borsu s hoof. 

box. When the foot rises, 

the inertia of the ball produces in its turn a compression 
by a kind of mechanism already described with reference to 
fig. 28. 

Through the kindness of Mons. Pellier, we have been able 
to experiment on several horses, ridden by himself, while 
holding in his hand the registering instruments. 



"When tlidiorse had his feet furnished with tlie india-rubher 
boxes which have just been described, thick transmitting 
tubes not easily crushed were iitted to these receptacles. 
These tubes art- usually 1'isteiiel by flannel hands to the le^.s 
oC llie animal, and thence directed to a point of alta-hment 
;il the level c>f the withers; they are then coul inued to the 
registering apparatus, which has been already described 
in the experiments on biped, locomotion. The registrar now 

I'M; il. Tliis fig"re represents R trotting hors- 1 , fumislx-d with thedlfibreot 

r\)Tiiiii'iit il i]i>|- ntni'iils ; tin- lini-MMii in c:n Tvni'.- tin' ri'i'i-li-r <>f the 

JMCr. llntlu: .,11(1 I In- .-iIX 1 il^triUIH-l.t.s lnHlniWtl, 


carries a j^reat iMimber of levers ; he must have four at -one for each of the le^s, and usually two other levers 
which receive their movements <,f re-action from the withers 
and the croup. Similar kinds of apparatus to tli-ise repre- 
sented in l\'^. 'JS are employed for this purpose. 

The rider carries hyihe handle a portable registering in- 
strument, 1o which all the levers ^i\e their signals at once; 
the han I wliich holds the reins is also ready to t-ompve^s a 


l>all of india-rubber at the moment when the horseman wishes 
the tracings to commence. Fig. 44 represents the general 
arrangement of the apparatus at the moment when the rider 
is about to collect the graphic signals of any particular pace. 



Double aim of these experiments : determination of the movements under 

the physiological point of view, and of the attitudes with reference 

to art. 
Experiments on the trot Tracings of the pressures of the feet and of the 

re-actions Notation of the trot Piste of the trot Representation 

of the trotting horse. 
Experiments on the walking pare Notation of this kind of motion ; its 

varieties Piste of the walking pace Representation of a pacing 


THE aim of these experiments is twofold; as far as 
physiology is concerned, we derive from them the expression 
of the duration, actions, and re-actions of each pace, the 
energy and duration of each movement, and the rhythm of 
their succession. But the artist is no less interested in 
knowing exactly the attitude which corresponds with each 
movement, in order to represent it faithfully with the various 
pnscs which characterise it. All these details are furnished 
by the registering apparatus; the artist need fear no error if 
he conform his sketches to the indications furnished by the 
tracings made by the instrument. 

The remarkable work of Vincent and Goiifon was expressly 
intended to establish principles relative to the faithful repre- 
sentation of the horse. We shall borrow some tilings from 
this book, which seems to have been too much forgotten, and 
not to have exercised upon art the influence that might havo 
been expected. This is doubtless owing, in some degree, to a 
certain obscurity in the mode of explanation, and still more 
to the fact that the writers, having had recourse only to direct 


observation in order to analyse the paces of the horse, have 
not Leen able to give all the details. We trust that we shall 
be more fortunate in our treatment of the subject; but we are 
assured, at le^st, of the perfect exactitude of the data fur- 
nished by the apparatus which we have used. 

Colonel Duhousset has been kind enough to offer us his 
assistance in representing the horse in its various paces ; it is 
to his skilful pencil that we owe tlic figures represented in this 
chapter, which are the faithful translation of the notation 
which accompanies them. We aie also indebted to Mons. 
Duhousset for some documents relating to the representation 
of the p;iccs. 

The knowledge of the pistes that is to say, the impressions 
which the feet of the horse leave on the ground is of great 
importance ; they enable an experienced eye to recognise the 
pace of the aniinnl which lias marked them. 

These pistes are of extreme value to the artist; they 
alone can represent to him the limbs as they strike the ground, 
with the true distances which they ought to preserve from 
each other according to the size of the horse and the speed of 
the pace. We refer the reader to the works of Vincent and 
Goiffon, of Baron Curnieu, of Colin. &c., on this subject, con- 
tenting ourselves with giving merely, from these writers, the 
jilste which characterises each pace. 

The first series of experiments, the results of which we are 
about to analyse, were made in the riding school of Mons. 
Pellier, fits. The horses were furnished, on each foot, with 
iin instrument for determining pressures, similar to that which 
is represented in fig. 42. We shall first discuss the experi- 
ments on the trot; the tracings which they give are easy to 
be understood ; the study of these will serve as a preparation 
ibr the more complicated analysis of the other pacjs. 


F.rjwimeiit* on the tint An old and very quiet horse fur- 
nished the tracing represented in fig. 45. In this plate are 
shown at the same time the tracings of the pressures of the 
four feet with their notations, and on the other side, the re- 
actions produced on the horse by this kind of pace. 



Let us analyse the details of these curves. Above are the 
re-actions taken from the withers for the fore part of the 



7 a 

t- m 

if: 71 


-t- OJ 


a z 





nnininl, which aro given liy iho lino RA (anterior re-nctions), 
and from the croup for the hinder part, which correspond 
with the line R P (posterior re-actions). 

Below are given the curves of pressure of the four feet ; 
llioy are drawn at two different levels; ahove are the curves 
of the anterior, below those of the posterior limbs. In each 
of these series the curves of the left foot are drawn -with 
dotted linos, those of the right with full lines. Whether 
dotted or full, these lines have been made thicker for the 
fore-limbs than for the hinder ones ; this difference, though 
of little use in curves as simple as those of the trot, will 
serve to render the more complicated tracings much more 

The moment whrn the curve begins its rise, represents the 
commencement of the pressure of the foot on the ground. 
The instant when the curve descends again gives the signal 
of the rise of the foot.* It is seen from these tracings 
that the feet A G and P D, left fore-foot and right hind foot, 
strike the ground at the same time. The simultaneous lower- 
ing of the curves of the two feet shows that they also rise from 
the ground simultaneously. Under these curves is the nota- 
tion which represents the press -ire of the left diagonal biped. f 

The second impact is given ly the feet AD and P G (right 
diagonal biped), and so oil through all the length of the 

This experiment confirms the correctness of the standard 
theory of the trot, and at the same time affords additional 
information on some points. Thus, all writers agree in 
choosing, as the type of the free trot, the pace in which all the 
four feet give but two strokes, and in which the ground is 
struck in turn by the two diagonal bipeds. It is admitted 

1 Tin- duration of the pressure ought to bo marked by a horizontal liiif, 
but \vc liavc made the tube somewhat narrow in ordi-r to lessen the fi'ivc 
of the shocks given to the registering lever ; the narrowing of the tube 
has sightly affected the curve, which, however, produces no inconvenience 
in studying the rhythms. 

t Each diagonal bi|d is named after the anterior foot of which it forms 
a part ; the left diagonal bijcil means, th'.Tclure, left fore foot, riyht liind 


also that the trot is a high pace, and that, in the interval 
between two successive strokes, the animal is for an iustaut 
raised above the ground. 

But we find disagreement when we come to estimate the 
duration of this suspension. Thus, according to Bouley, it is 
very short in proportion to the duration of the pressure ; 
whilst RaaLe thinks, on the contrary, that the pressure is 
very short, so that the animal is a longer time in the air than 
on the ground. 

In the notation of the tracing (fig. 45), it is peen that the 
pressures are twice as long as the periods during which the 
body is suspended above the ground. This experiment, there- 
fore, would confirm the opinion of Bouley in opposition to 
that of Raabe ; but it appears to us that there is a great 
variety in the relative duration of the pressures, and of the 
periods of suspension above the ground during the trot. 
Thus, certain horses running in harness have furnished 
tracings in which the phase of suspension was scarcely 
visible ; so that this form of trot resembled the low paces, 
only preserving that characteristic of the free type which 
arises from the perfect synchronism of the diagonal strokes of 
the feet. We have not yet been able to study the movements 
of rapid trotters ; iu these perhaps we should see, in an 
inverse ratio, the time of suspension, increase over that of the 
duration of pressures. 

If we siM-k to ascertain the correspondence between the 
re actions (II A and 11 P) and the movements of the limbs, we 
see that the moment when the body of the animal is at the 
lowest part of its vertical oscillation coincides precisely with 
that at which its feet touch the ground. The time of suspen- 
sion does not depend on the fact that the body of the horse is 
projected into the air, but that all four legs are bent during 
this short period. The maximum height, of the suspension of 
the body corresponds, on the contrary, willi the end of the 
pressure of the limbs on the ground. It seems, according to 
the tracings, that the elevation of the body does not com- 
mence till after each double impact, and that it continues 
during the whole time of the pressure. 

It is also seen, in the same figure, that the re-actions of the 



fore-limbs are much more considerable tliau those of the 
hinder ones. This fact appears to us to lie constant ; and the 
inequality of the re-actions is still more marked in tl:" walk- 
ing pace, her. HIM- the apparatus placed on the \vilhers almost 
always gives appreciable re-actions, while that on the croup 
gives scarcely any. 

( >/' tin- iri'i'iniliir tn.t (tint decOUStl). We call that alive 
trot which gives two distinct sounds to the ear fi r each pace, 
and we name that irregular, each of which is in a cer- 
tain degree divided hy the want of synchronism in the strokes 
of each diagonal biped. The irregular trot has been met, 
with in many of our experiments. Occasionally this pace; was 
continued, and then the want of synchronism existed SOUK - 
times in the impacts of the two diagonal bipeds, and some- 
times in one pair only; at other times, on the contrary, tlio 
trot was irregular only for an instant, at the moment of tin- 
passage from one kind of pace to another. In nil the experi- 
ments which we have hitherto made, the want of synchronism 
depended on the hinder limb being behind the anterior limb 
which corresponded diagonally with it. 

Fig. -It) represents the notation of an irn'yulitr trot, in 
which the diagonal impacts leave between them an appre- 
ciable interval of time. We can recognise this by the 
obliquity of the dotted lino which unites with each other the 
impacts of the t\vo diagonal bipeds. 

thu Irregular trot 

The jiixd- .f the trot is represented in fig. -17, according (o 
Vincent and (Joill'on. All the prints are double, for the 
hinder-foot al\\ays comes up to take the place of the lore-foot 
on the same i ide. 

In tig. 17 \\ e have rendered this Superposition imperfect 



in order to avoid confusion ; for the same purpose, we have 
represented the prints of the fore-feet by dotted lines, those of 
the hind-feet by full lines. In the trot, the prints of the left 
f et alternate perfectly with those of the right feet. 

FIG. 47. Piste of the trot according to Vincent and Guiffon. 

According 1 to the speed of the trot, and the size of the 
horse, the piste varies much with respee f to the space which 
separates the prints on the same side 

Fin. 48. Horse trotting with i low kind of pace. The instant corresponding 
with the attitude represented in this figure, is marked with a white dot 
on the not;iti' in. 

In the representation of the trotting horse we must dis- 
tinguish the different forms of this pace. 

The low and short trot is represented in fig. 48. We usually 



make our observations at the start of the animal, or at the 
liniment when he passes from the walking pace to the trot. 
The diagonal impacts succeed each other without interval, as 
is seen in the notation placed below the figure. The animal 
has been depicted from the notation. 

The instant which the artist has chosen is that which is 
marked in the notation by a white dot. At this moment, as 
the superposition indicates, the left fore-foot is at the end of 
its pressure 5 the right fore-foot is about to reach the ground ; 
the right hind-foot is finishing its pressure ; the left hind-foot 
is about to fall. The inclination of the limbs is that which 
corresponds with each of the phases of the pressures and the 
rise of the feet. The distance separating the feet is that 
which is indicated by the prints on the ground. Thus, in 
fig. 48, it is seen that the trot is shortened, for the hind-foot. 

Fio. 49. Horse nt full trot. The <lot plural in Ino notation corresponds 

with lli.- a't:ln.l<- iri'ivx lit. .1 


on the point of striking tlie ground, will nut reach the place 
of the fore-foot on the same side. 

The elevated and lengthened trot is represented in fig. 49, 
which hns already served to show the rider and his horse 
furiiisliLd with the ii:s ruments for the purpose of forming 
tracings of the various paces. The animal is depicted at the 
instant which, in the notation, is represented by a dot ; that 
is to say, during the time of suspension, at the moment when 
the left diagonal biped has just riseu and the right diagonal 
biped is about to descend. 


Experiments on the icalking pace. The explanations into 
which we have entered in order to analyse the tracings of a 
trot, will facilitate the interpretation of that of the walking 
pace, represented in fig. 50. These tracings have been obtained 
from the same horse as the preceding ones. 

If we let fall a perpendicular from tho points at which the 
curves commence, we shall have the position of tho successive 
impacts of the four legs. On account of the thickness of the 
style employed to trace these curves, the foot corresponding 
\\ith each of them is easily recognised, therefore we cau 
maik on each of these perpendicular lines the initial letters 
of the foot which at this moment reaches the ground. The 
order of succession of impacts is represented by the letters 
A I), P G, A G, P D ; that is to say, right fore-foot, left hind- 
fnot, left fore-foot, r'ujht hind foot, which is the succession 
admitted by writers on the subject. 

There remaius to be determined the greater or less regu- 
larity in the succession of these impacts, and the relative 
extent of the intervals which separate them. For this purpose 
it is sufficient to construct the notation of the rhythm, of the 
pressure of each foot according to the registered curves. 
This notation for fig. 50 shows that the interval which sepa- 
rates the impacts is always the same, and, consequently, that 
the horse rests during the same time on the lateral as on the 
diagonal bipeds. But this is not always the case. 

That we may render the successive positions of the centre 
of gravity easily understood, we will explain in few words the 



manner in which the notation of i\g. 50 lias lioon o<m>tructed. 
It' \VL- let 1'all perpendiculars ftrrcspmnling' with each of the 
























footfalls, beginning with that of the right fore-foot, which is 
marked No. 1, we shall divide the figures into successive por- 
tions, iu which will be found the impacts, sometimes of two 
legs on. the same side (lateral biped), at others, of t\vo placed 
diagonally (diagonal biped). Thus, from 1 to 2, the horse 
will rest on the right lateral biped ; from 2 to 3, on the right 
diagonal biped (that is to say, on that in which the riykt foot 
comes first] ; from 3 to 4, on the left lateral biped ; from 4 
to 5, on the left diagonal biped ; again, from 5 to 6, the horse 
would find himself, as at the beginning, on the right lateral 

This experiment has reference entirely to the standard 
theory of the pace (see No. 5 of the synoptical table), but 
some horses walk in a manner somewhat ditferent. 

Fig. 51 is the notation of the walking pace of a horse 
which rested longer on the lateral than on the diagonal 

Sometimes the contrary is observed ; in the transitions 
from the walk to the trot, for instance, we have found the 
duration of the diagonal pressures predominate. 

This study, in order to be complete, ought to have been 
carried on under more favourable conditions than those which 
Ave have hitherto been able to meet with. It would be 
desirable to obtain many horses belonging to different breeds; 
to study their movements when led by the hand, mounted, or 
harnessed ; to vary the load which they carry or draw ; to 
experiment on level or sloping ground, &c. All this can only 
be effected by men especially interested in these inquiries, and 
placed in favourable circumstances to undertake them. 

While making observations on draught horses, it has 
seemed to us that when the animal strives to re-act against 
the weight of the carriage pressing upon him, he may have 
three feet on the ground at once. This Borelli considered 
to be the normal walking pace ; we have just seen, on the 
contrary, that in the natural walking pace there are never 
more than two feet on the ground at a time. 

As to the re-actions during the walking pace, they are not 
represented in fig. 50. We have ascertained generally that 
the re-actions of the fore-limbs are the only ones of any iui- 



portanco ; we are led to suppose, by tlie extremely slight re- 
actions of the hinder parts, that their action consists ehielly 
in a forward propulsion, but with very slight impulsion of 
the body in an upward direction. This agrees with the theory 
somewhat generally admitted, by which the fore legs woidd 
have little to do in the normal pace except to support alter- 
nately the fore part of the body, while to the hiinl limbs 
would belong the propulsive action and the tractive force 
developed by the animal. 

The piste of the walking pace, according to Vincent and 
(ioilfon, is analogous with that of the trot, except that it pre- 
sents a shorter interval between the successive footprints on 
the same side. 

Fio. 52. riste of the walking pace, after Vincent and Goiffon. 

In the ordinary walk, this distance would be equal t> the 
height of the horse, measured at the withers. As in the trot, 
the prints are covered at each pace; those of the right foot 
alternate perfectly with those of the left. This character of 
the jnntc. of the walking pace is, however, observed only under 

Fio /;.'!. Pi.sto of flic ainlilr. after Vincent and (ioiffon : it differ* from that 
cif tlio walking )> nv. only liy tin. 1 7n ni sii] in im-itnm of tlic footjiri'its on 
tin 1 Mum- Mile. Tin' liiii't fimt is placed on tbo groun.l beyond i ho im- 
:iin t tlio fo.u foot. 

certain conditions of speed, and on level ground. On rising 
ground the prints of the hind-feet are usually behind those of 
the fore -feet ; in a de-cent, on the contrary, they may possibly 
pa;-s bevond them, vhicli would give the jtistc of the walk 
some itv-rml, lance to that of the amble. 



Representation of a pacing horse. The representation of a 
horse at the walkiu^ pace has been given by Moiis. Duhousset 
in tig. 54. The instant chosen is marked iti the notation by 
a dot. We shall not give an enumeration of the positions of 
the limbs of the animal as shown in the notation, as we have 
already done so in the representation of the trot. 

FIQ. 54. Representation of the liorse at a walking pact. 




Experiments on the gallop Notation of the gallop lie-actions Bases of 

support Pistes of tlie gallop Representation of a galloping horse in 

the various times of this pace. 
Transitions, or passage, from one step to the other Analysis of the paces 

by means of the notation rule Synthetic reproduction of the 

different paces of the horse. 


SEVERAL different paces, the common character of which is 
Unit irregular impacts return at regular intervals, are compre- 
hended under this name. Most of the writers distinguish 
three kinds of gallop by the rhythm of the impacts, nud 
name them, according to this rhythm, gallop in tiro, three, 
iiwl/r time. The most ordinary hind is the gallop in three- 
time ; this we shall study in the first place. 

Experiments on the gallop. Fig- 55 has heen obtained from 
a horse which galloped in three-time. At first sight, tho 
notation of this pace reminds us of that which wo have 
represented when speaking of human gallop (fig. 36, p. 13-1), 
a pace used by children when " playing at horses." It 
appears that the notation of the horse's gnllop has been 
obtained by placing one over another two of these notations 
of tho biped gallop; so that, in fact, the comparison used by 
Duges is perfectly just, even \\lien it is applied to the gallop. 

Analysis of the tracing. At the commencement of the figure, 
the animal is suspended above tho ground ; then comes tho 
impact P O, which announces that the left hind-foot touches 
the ground. This is the foot diagonally opposed to that which 
the horse places forward in the gallop, and whose impact A D 
will be produced the last. Between these two impacts, and 
distinctly in the middle of the interval which separates them, 
comes the simultaneous impact of tho two feet forming the 



left diagonal biped. The superposition of the notations A G, 
P D, clearly shows this synchronism. 


In this series of movements the ear lias, therefore, dis- 
tinguished three sounds, at nearly equal intervals. The first 
sound is produced by a hinder foot, the second by a diagonal 
biped, tin; third by a fore-foot. Between the single impact of 
the fore-foot, which constitutes the third sound, and the first 
brat of the pace which follows, reigns a silence whose dura 
tion is exactly equal to that of the three impacts taken 
together; then the series of movements recommences. 

By the inspection of the curves, we see that the pressure 
of the feet on the ground must be more energetic in tin- 
gallop than in the other paces already represented, for the 
height of ihe curves i.s evidently greater than for the trot, 
and especially so as compared with the walk. In fact, the 
animal must not only support the weight of its body, but give 
it violent forward impuU.cs. The greatest energy seems to 
belong to the first impact. At this moment, the body, raised 
for an instant from the ground, falls again, and one leg 
alone sustains this shock. 

Fio .V, 0:illn]i in tliroo-tiinc (A) imlicition of tlircu-time. B. indication 
of I lie iiiinii'cr of ti'et wliich form tlie support ot tbe body at cacti instant 
of tlic gallop in three timo. 

If we wish to take account of the successive pressures which 
sustain the body during each of the steps in the gallop, we 
have only to divide the duration of this pace into successive 
instants in which the body is sometimes supported on one or 
on several feet, and sometimes suspended. The notation (fig. 
50) allows us to follow in (A) the succession of impacts, and 
shows in (B) the succession of the limbs wliich cause these 
pressures on the ground. 

II wo wish to ascertain what are (he rr-iictimis produced nt 
the withers, we see them represented in lig. '>'> Cupper line K 
We find an undulatory cle\ ; uioii, \\hich lasts all the tune 



that the animal touches the ground; in this elevation are 
recognised the effects of the three impacts, which give it a 
triple undulation. The minimum elevation of the curve cor- 
responds, as in the trot, \\ith the moment when the feet do 
not touch the ground. Therefore, it is not a projection of the 
liody into the air which constitutes the time of suspension iu 
the gallop. Lastly, by comparing the re actions of the gallop 
with tluxse of the trot (fig. 45), we see that in the gallop the 
rise ai.'d fall of the body are effected in a less sudden manner. 
These re-actions are, therefore, less jarring to the rider, 
though they may, in fact, pi'esent a greater amplitude. 

Piste of the gallop in three-time. According to Curnieu, this 
piste is the following : 

FIG. f>7. Fistc of tbe short gallop in tliree-time. The hindc r feet, whose 
prints have the f Tin of 1111 U, reach the ground in front of tlje piinis of 
the fore ftet. Thu latter have been represented by a form souiewliiit like 
an O. 

The piste of the gallop varies according to the speed. In 
the short gallop of the riding school, the hind-feet leave their 
prints behind those of the fore-feet ; in the rapid gallop, on 
the contrary, they come in front of the prints of the fore-feet. 
A horse which, in the pace of the riding school, gallops 
almost entirely within his own length, will, when started at 
full gallop, cover an enormous space. According to Curnieu, 
the famous Eclipse covered 22 English feet. The following 
is the piste which this very rapid pace leaves on the ground : 

FIG. f S. Piste of B-ttpie's gallop, from Curnieu. The prints of the hind- 
feet are very far before those of the fore-feet. 

Representation of a horse galloping. For this representation 
we will give three attitudes, differing much from each other, 



and corresponding nearly with the three kinds of time found 
in this pace. 

l'"lo. "9. H< TSC crrvlloping in tlicfirst tiimfYi^ht foot advancing), the liind left 
foot only on the ground. The white dot, in the nutation, 
with the instant at which the horsois represent r. I 

In the first time, fig. 59, the loft hind-foot, on which the 
horse has just descended, alone rests on the grouu.l. 

In the second time, fig. 00, the left diagonal bipod has just 
finished its impact, the right fore-foot is about to reach the 
ground, the left hind-loot has just risen. 

The third time of the gallop, iig. 01, has been drawn as 
well as the others by Mons. Dulmnssrt according to tin- nota- 
tion; the moment chosen is that in \\hieh the right foot 
alone rests on the ground, and is about to list 1 in ita turn. 



TIG. GO. Horae galloping in the second time (right foot forward). 

Fro. 61. Horse galloping in the third time (right f 'ot forward). 



The figure which represents it is rather si range ; the eye is 
luit little accustomed to see this time of the gallop, which is 
doubtless very run;. When considering this ungraceful figure, 
we are lempted to say with De Curnieii, "the province of 
painting is what one sees, and not what really exists." 

The gallop in four-time differs from that which has just 
I'een described only iu this point, that the impacts of the 
diagonal biped, which constitute the second time, are disunited 
and give distinct sounds ; we see ail example of this in tig. 62. 

Fir.. I'.-j Xnt.-itiiiu of the gallop in four tune. (A) determination of each 
of the successive times. (15 determination of the number of feet which 

support tlio body :it c:n.'h 

According to this notation, the body, at Srst suspended, is 
borne successively on one foot, on three, on two, on three, and 
on one, after which a new suspension recommences. 

(>/' tin' full ij<ill(i}>. This very rapid pace could not lie 
studied by means of the apparatus which we have employed 
hitherto. It was necessary to construct a special registering 
instrument, and new experimental apparatus. 

To leave the two hands of the rider free, the registering 
instrument was enclosed in a flat box, attached to the back of 
the horseman by straps like the knapsack of the soldier. We 
shall not attempt the detailed description of this instrument, 
which carried five levers, tracing on smoked glass the curves 
of the action of the four le^s, and the reaction of the withers. 
The violence of the impacts on the ground is such that they 
would instantly have broken the apparatus before employed. 
We have, substituted for this a copp.T tube, in which moves a 
leaden piston, suspended between two spiral springs. The 
shocks given to this pistrm at each footfall, produce an effect 
like that of an air-pump acting on the registers. A ball of 
india-rubber, which can be pressed between the teeth, sets the 


register going-, and allows the tracing to Le taken at a suitable 

Through the kindness of Mons. II. D lamarre, who placed 
at our disposal his stables at Chautilly, we have been able to 
procure tracings of the full gallop, of which the following is 
the notation : 

FIG. 03. Notation of full gallop; re-actions of this pace. 

It is seen that this pace is, in reality, a gallop in four-time. 
The impacts of the hinder limbs, however, follow each other 
at such short intervals, that the ear can only distinguish one 
of them ; but those of the fore-legs are noticeably more dis- 
sociated, and can be heard separately. Another character of 
the full gallop is, that the longest period of silence takes 
place during the pressure of the hinder limbs. The time of 
suspension appears to be extremely shoi't. 

To get the best possible results from these experiments, it 
would be necessary to repeat them on a great number of 
horses, and to ascertain whether there may not be some rela- 
tion between the rhythm of the impacts and the other 
characters of the pace. We must leave this task to those 
who especially addict themselves to the study of the horse. 

Lastly, let us add, that the re-actions, in full gallop, repro- 
duce with great exactness the rhythm of the impacts. Thus, 
it is observed, that at the moment of the almost synchronous 
impacts of the two hinder limbs, there is a sharp and pro- 
longed re-action, after which two less sudden re-actions take 
place, each of which corresponds with the impact of one of 
the fore-legs. 

The line placed above fig. 63 is the tracing of the re-actions 


of (lie withers. This curve, being placed above the notation, 
enables us, by the superposition of its various elements, to 
notice with which impact of the limbs each re-actioii cor- 



An observer finds great difficulty in ascertaining how one 
kind of pace passes into another. Tlie graphic method fur- 
nishes a very easy means of following these transitions; this 
will perhaps lie not one of the least advantages of the employ- 
ment of this method of studying the paces of the horse. 

In order thoroughly to understand what takes place in these 
transitions, we must refer again to the comparison made by 
Duges, and represent to ourselves two persons walking, and 
following each other's footsteps, both in the trot and the 
gallop. In these continued paces, these two persons present 
a constant rhythm in the relation of their movements ; \\hile, 
in the transitions, the foremost or hindermost person, as the 
case may be, quickens or moderates his movements so as to 
change the rhythm of the footfalls. Some examples will 
rentier this more evident. 

The principal transitions are represented in page 174. 

r'ig. G 1 is the notation of the transition from the walking 
pace to the tmt. The dominant character of this change, inde- 
pendently of the increase of rapidity, consists in the hinder 
impacts gaining upon those ot the fore-limbs; so that the 
impact of the left hind-foot, P G, for instance, which, during 
the walking pace, took place exactly in the middle of the 
duration of the pressure of the right fore-foot, A D, gradually 
advances till it coincides with the commencement of the 
pressure A D, and with the impact also, at which time the 
trot is established. 

Fig. G5 indicates, on the contrary, the transition from the 
tmt to the walk. We see here, in an inverse manner, the 
diagonal impacts, synchronous at first, become more and more 
separated. A dotted line, which unites the left diagonal 
impacts, is vertical at the commencement of the figure in the 
part which corresponds with the pace of the trot; by degrees 


this line becomes oLlique, showing that the synchronism is 
disappearing 1 . The direction of the obliquity of this line 
proves that the hinder limbs grow slower in their movements 
in passing from the (rot to the. walk. 

In the passage from the trot to the gall p the transition is 
very curious; it is represented by the notation, fig. CO. We 
see, from the very commencement of (lie figure, that the (rot 
is somewhat irregular ; the dottud line which unites the left 
diagonal impacts A G, P D, is at first rather oblique, and in- 
dicates a slight retardation of the hind-foot. This obliquity 
constantly increases, but only for the left diagonal biped ; the 
right diagonal biped A D, P G, remains united, even after 
the gallop is established. The transition from (he trot to the 
gallop is made, not only by (he retardation of the hind-foot, 
but by the advance of the fore-foot, so that two of (he diagonal 
impacts, which were synchronous in (he trot, leave (he greater 
interval between them ; that which in the ordinary gallop con- 
stitutes the great silence. An opposite change produces the 
transition from, the gallop to the trot, as is seen in fig. 67. The 
transition from the gallop in four-time to that in three-time is 
made by an increasing anticipation of the impacts of the 
hinder limbs. 


The analytical method to which we have hitherto had 
recourse in describing the paces of the horse may have left 
many things obscure in this delicate question. We hope to 
clear them up by recurring to the synthetic method. 

When tracing, at the commencement of (his study, (he 
synoptical table of the different paces, we classed their nota- 
tions in a natural series, the first term of which is the amble, 
and in which the difference between one step and the next 
consists in an anticipation of the action of (he hinder limbs. 
This transition is just what is observed in animals. A drome- 
dary, for instance, whose normal pace is the broken amble,* 

* Through the kindness of Mons. Geoffrey St. Ililaire, director of the 
" Jardin d'Acclimatation," we have been permitted to study the paces of 
different quadrupeds, and especially tluse of the large dromedary which 
lliat garden possesses. 



C '" i; to 


lias given iis the -whole series of notations, which, in our 
synoptical table, separate No. 2 from No. 8. When urging 
on the animal and forcing him to trot, he first broke his amble 
in an exaggerated manner, then he began to walk, and after- 
wards commenced an irregular trot, which soon became a free 
trot. We have just seen that the paces of the horse are formed 
in the same order when the animal passes from the walk to 
the trot. 

When a horse begins to move more slowly, the change of 
pace is effected in an inverse manner ; the paces succeed each 
other by running up the series represented in the plate. 

The greater or less anticipation of the action of the hinder 
limbs is represented in the plain by a sliding backward of the 
notation towards the left of the figure. This fictitious sliding 
may become real by using a liltle instrument, which enables 
us to understand and explain very simply the formation of the 
different paces. It consists of a little rule, somewhat analo- 
gous to the sliding rule used in calculation, and which carries 
the notations of the four limbs on four little slips, which can 
glide side b\ side, and be arranged in various positions. 

Fio. 08. Notation rule, to represent the different paces. 

68 and 69 show the arrangement of this little instru- 

O < ~ } 

incut. Let us imagine a rule made of black wood, having 
four narrow grooves, in which slip sliding portions, alternately 
black and white, or grey and black, in order to represent the 
notation of the amble, as in No. 1 of the plate. If we push 
towards the left the two lowest slides simultaneously (fig. 68), 
we shall form, according to the amount of displacement, one 


or otlier of the notations in the tal>le of regular paces. A 
scale, marked 1, 2, ;!. I. &c., np to which we can bring the 
mark representing the left liintler impact, allows us to form 
without hesitation any notation whatever. 

To form tin- notations of the gallop, it is necessary to shift 
the slides corresponding with the fore-legs, so as to make 
them encroach ou each otlier as is seeu in notation, fig. 69. 

FIG. 69. Notation rule forming the reprenentation of the j.';ill..p in thrce- 


The notation rule is thus used. When we are sure that 
the pace is regular, it is sufficient, for instance, to examine 
the impacts of the two right feet, in order to construct the 
whole notation. According as the hinder impact is synchro- 
nous with that in front, or precedes it hy a quarter, half, 
three-quarters, or the whole of the duration of a pressure, we 
place the two lower slides in the position which they ought to 
occupy, and the notation is thus simplv constructed; it shows 
the rhythms of the impacts, the duration of the lateral and 
diagonal pressures, &<. The construction of the various 
paces of the gallop is effected in the same manner. 

The artist who wishes to represent a horse at any instant 
of a particular pace, can thus easily determine the correspond- 
ing attitude. He forms on his rule the notation of the pace 
of the horse which is to lie represented. Then, on the length 
which corresponds with the extent of a single pace in this 
notation, he erects a perpendicular line at any point. This 
line corresponds with a certain instant of the pace. Thus, as 
he can trace, on the length corresponding with a single pace. 


an indefinite number of perpendicular lines, it follows that the 
artist may choose in the duration of any pace, in any kind of 
locomotion, an indefinite number of different attitudes. Sup- 
pose him to have made his choice, and that he wishes to 
represent in the kind of pace (fig-. 68), the instant which is 
marked by the vertical Hue 7, the notatiou will show him that 
the right foro-foot has just been placed upon the ground, that 
the left fore-loot is therefore beginning to rise, that the right 
hind-foot is almost at the end of its pressure on the ground, 
jind that the left hind -foot is near the end of its rise. All 
that is necessary, in order to represent the animal exactly, is 
to know the attitude of each limb at the different instants of 
its rise, fall, or pressure, which is a comparatively easy matter. 
But the artist, guided by this method, will thus inevitably 
avoid altogether those false attitudes which often cause repre- 
sentations of horses to be so utterly unnatural. 


Mons. Mathias Duval has undertaken to make, in order to 
illustrate the locomotion of the horse, a series of pictures, 
which, seen by means of the zootrope, represent the animal 
as if in motion in the various kinds of paces. This ingenious 
physiologist formed the idea of reproducing in an animated 
form, as it were, that which notation has done for the rhythm 
of the movements. The following is the arrangement which 
he employed, lie first, drew a series of figures of the horse 
taken at different instants of an ambling pace. Sixteen suc- 
cessive figures enabled him to represent the series of positions 
which each limb successively assumes in a pace belonging to 
this kind of locomotion. This baud of paper, when placed 
in the instrument, gives to the eye the appearance of a.n 
ambling horse in actual motion. 

We have said that all the walking paces may be considered 
as derived from the amble, with a more or less anticipation of 
the action of the hind limbs. Mons. Duval has realised this 
in his pictures in the following manner. Each plate, on 
which lias been drawn the series of pictures of the ambling 
horse, is formed of two sheets of paper placed the one on the 
other. The upper one has in it a number of slits or openings, 


so that e;icli horse is drawn half on this sheet, and the other 
half on that which is placed beneath. The hind quarters, 
for example, having been drawn on the upper sheet, the fore 
quarters are drawn on the under sheet, and are visible through 
the portion cut out of the upper sheet. Let us suppose that 
we cause the upper paper to slide as far as the interval which 
separates two figures of the horse, we shall have a series of 
images in which the fore limbs will full back a certain dis- 
tance towards the hind limbs. We shall thus represent, 
under the form of pictures, what is obtained under the form of 
notation, by slipping the two lower slides of the notation rule 
one degree. And as this displacement to the distance of one 
degree for each of the movements of the hinder limbs gives 
the notation of the broken amble, we shall obtain, in the 
figures thus drawn, the series of the successive positions of 
the paces of the broken auible. If the paper be made to slip 
a greater number of degrees, we shall have the series of atti- 
tudes of the horse at his walking pace. A still greater dis- 
placement will give the attitudes of the trot. 

In all these cases, these figures, when placed in the instru- 
ment, make the illusion complete, and show us a horse which 
ambles, walks, or trots, as the case may be. Then, if we 
regulate the swiftness of the rotation given to the instrument, 
we render the movements which the animal seems to execute 
more or less rapid, which will permit the inexperienced 
observer to follow the series of positions of each kind of pace, 
and soon enable him to distinguish with the eye a series of 
movements in the living animal which appear at first sight to 
be in absolute confusion. 

We hope that these plates, though still somewhat defective, 
will soon bo sufficiently perfect to be of real use to those who 
are engaged in the artistic representation of the horse. 

After these studies of terrestrial locomotion, we ought to 
explain the mechanism of aquatic locomotion. Some rect-nt 
experiments of Mons. Ciotti have thrown great light on the 
propulsive action of the tails of fishes; not that they have 
overthrown the theory held ever since the time of Borelli, 
concerning the mechanism of swimming, but they have ap- 
proached the question in another manner, that of the synthetic 


reproduction of this phenomenon. This method will certainly 
permit us to determine, with a precision hitherto unknown, 
both the motive work and resistant work in aquatic 
locomotion. It will, therefore, be advisable to wait for the 
results of experiments which are now being made, and 
which will be of equal service both to mechanicians and to 





Frequency of the strokes of the wing of insects during flight; acoustic 
determination ; graphic determination Influences which modify the 
frequency of the movements of the wing Synchronism of the action 
of the two wings Optical determination of the movements of the 
wing ; its trajectory ; changes in the plane of the wing ; direction 
of the movement of the wing. 

IN terrestrial locomotion we have been able to measure by 
experiment the pressure of the feet on the ground, and hence 
we have deduced the intensity of the re-actions on the body 
of the animal. These two forces were easily ascertained by 
direct measurement. In the problem which is now to occupy 
us, the conditions are very different. The air gives a certain 
resistance to the wings which strike upon it, but it is a resis- 
tance every instant yielding, for it is only in proportion to the 
rapidity with which it is displaced, that the air resists the 
impulse of the wing. When we study the phenomena of flight, 
it is therefore necessary to know the movement of the wing in 
all the phases of its speed, in order to estimate the resistance 
which the air presents to that organ. We will propound in 
the following order the questions which must be resolved. 

1. What is the frequency of the movements of the wing of 
insects ? 

2. What are the successive positions which the wing occu- 
pies during its complete revolution ? 


3. IIo\v is the motive force which sustains and transports 
the body of the animal developed ? 

1. Frequency of the movements of the winy of insects The 
frequency of the movements of the wing varies according to 
species. The ear perceives an acute sound during- the flight 
of mopquitos and certain flies ; there is a graver sound during 
the flight of the bee and the drone fly ; still deeper in the 
inacroglosstu and the sphingidro. As to the other lepidoptera, 
they have, in generul, a silent flight on account of the few 
strokes which they give with their wings. 

Many naturalists have endeavoured to determine the fre- 
quency of the strokes of the wing by the musical note pro- 
duced by the animal as it flies. But in order that this deter- 
mination should be thoroughly reliable, it must be clearly 
established that the sound produced by the wing depends 
exclusively on the frequency of its movements, in the same 
manner as the sound of a tuning-fork results from the fre- 
quency of its vibrations. But opinions differ on this subject; 
certain writers have thought that during flight there is a 
movement of the air through the spiracles of insects, and that the 
sound which is heard depends on these alternate movements. 

Without giving our adherence to this opinion, which 
seems to be contradicted by many f;icts, we think that the 
acoustic method is insufficient to furnish an estimate of the 
frequency with which the wing moves. The reason which 
would induce us not to employ this method, is that the 
musical note produced by the flying insect is varied by other 
influences besides the changes in the "strokes of the wing. 

When we observe the buzzing of an insect flying with a 
uniform rapidity, we perceive that the tone does not continue 
constantly the same. As the insect approaches the ear, the 
tone rises; it sinks as it goes farther from us. Something of 
an analogous kind happens when we cause a vibrating 
tuning-fork to pass before the ear; the note at first becomes 
more shrill and then more grave, and the difference may 
attain to a quarter or eveu to half a tone. We must, there- 
fore, take care that the insect on whicli we experiment should 
be always at the same distance from the observer. This dis- 
turbing phenomenon, however, presents no real difficulty of 


interpretation ; Pisko, tlie German writer on acoustics, lias 
perfectly explained it. There is no doubt that the vibrations 
always follow each other after the same interval of time ; when 
a vibrating plate remains at the same distance from the ear, 
the vibrations require the same time to reach us, and the 
phenomenon, uniform for the instrument, is uniform also fi;r 
our organ. On the contrary, if the instrument be brought 
rapidly nearer, the vibration which is produced every instant 
lias less space to traverse before it reaches the tympanum; it 
thus approximates to that which preceded it, and the sound 
grows sharper. If the instrument be removed to a greater 
distance the vibrations are more extended, and the lone be- 
comes more grave. Everyone has remarked, when travelling 
on a railroad, that if a locomotive passes us while the driver 
is sounding the whistle, the shaipne^s of the tone increases as 
the engine comes nearer, and becomes graver when it has 
passed by us, and the whistle is rapidly carried to a greater 

From these considerations we must be convinced that it is 
very difficult to estimate from the musical tone produced by 
a flying insect, the absolute frequency of the strokes of its 
wings. This depends to some extent on the variation of the 
tone thus produced, which passes at each instant from grave to 
sharp, according to the rapidity and the direction of (he flight. 
Besides this, it is not easy to assign to each wing the part 
which it plays in the production of the sound. "\Ve have also 
to take into consideration that the wing of an insect may, by 
brushing through the air as it flies, be subjected to sonorous 
vibrations much more numerous than the complete revolutions 
which it accomplishes. 

The graphic method furnishes a simple and precise solution 
of the question; it enables us to ascertain almost to a single 
beat the number of movements made per second by an insec t's 

Experiment. A e-heet of paper blackened by the smoke 
of a wax-candle, is stretched upon a cylinder. This cylinder 
turns uniformly on itself at the rate of a turn in a second 
and a -half. 

The insect, the frequency of the movement of \\hoso wings 


is to be studied, is held by the lower part of (lie abdomen, in 
a delicate pair of forceps ; it is placed in such a manner that 
one of its wings brushes against the blackened paper at every 
movement. Each of these contacts removes a portion of 
the black substance which covers the paper, and, as the 
cylinder revolves, new points continually present themselves 
to the wing of the insect. \Ve thus obtain a perfectly regular 
figure, if the insect be held in a steadily fixed position. These 
figures, of which we give some examples, differ according as 
the contact of the wing with the paper has been more or 
less extended. If the contact be very slight, we obtain a 
series of points or short cross-lines, as in fig. 70. 


Fio. 70. Showing the frequency of the strokes of the wing of a drone-fly 
(the three upper lines), and of a bee (the lower dotted line'. Thi foil th is produced by the vibrations of a chronographic tuniir-'ork, fur- 
nished with a style which registers 250 double vibr.itions per second. 

Knowing that the cylinder revolves once in a second and 
a-half, it is easy to see how many revolutions of the wing 
are thus marked on the whole circumference of the cylinder. 
But it is still more convenient and accurate to make use of a 
chronographic tuning-fork, and to register, near the figure 
traced by the insect, the vibrations of the style with which 
the tuning-fork is furnished. 

Fig. 70 shows, by the side of the tracing made by the 
wing of a drone-fly, that of the vibrations of a tuning fork, 
which, executes a double oscillation 250 times in a second. 
This instrument, enabling us to give a definite value to any 
portion of the tracing, shows that the wing of the drone per- 
formed from 240 to 250 complete revolutions per second. 


Influences which modify the frequency of the movements of the 
U'UKJ. Since we know the influence of resistance to the rapidity 
dt' the movements of animals, \ve may suppose that the wing 
which rubs on the cylinder has not its normal rate of motion, 
arid that its revolutions are less numerous iu proportion as 
the friction is greater. Experiment lias confirmed this opinion. 
An insect performing the movements of flight by rubbing its 
wings rather strongly against the paper gave 240 movements 
per second ; by diminishing more and more the contacts of 
the wing with the cylinder, we obtained still gi-eater numbers 
282, 305, and 321. This last number may perhaps ex- 
press with sufficient accuracy the rapidity of the wing when 
moving freely, for the tracing was reduced to a series of 
scarcely-visible points. On the contrary, as the wing rubbed 
more strongly, the frequency of its movements was reduced 
below 240. 

Another modifying cause of the frequency of movement iu 
the wing is the amplitude of those movements. We must 
compare this cause with the preceding, for it is natural to 
admit that great movements meet with greater resistance in 
the air than smaller ones. 

AYhen \\e hold a fly or a drone by the forceps, we see that 
the animal executes sometimes strong movements of flight; 
we then hear a grave sound; but occasionally, when its wing 
is only slightly agitated, \ve perceive only a very shrill tone. 
That which the ear reveals to us with regard to the difference 
in the frequency of the strokes which the insect gives with its 
wings, is entirely confirmed by the experiments which wo 
have made graphically. 

Choosing the instants when the insect is at its strongest 
(light, and also when it gently flutters its wing, we find that 
the frequency varies within very extensive limits, nearly in 
llie proportion of one to three the least frequency belonging 
to the movements of greatest amplitude. 

The different species of insects on which we have experi- 
mented, presented also very great variations in the rapidity of 
the movements of their wings. We have endeavoured as far 
as possible to compare the different species under similar con- 
ditions, during their swiftest flight, aud with slight friction 


on the cylinder. The following are the results obtained as 
the expressions of the number of movements of the wing per 
second in each species : 

Common fly 330 

Drone-fly ... . . 240 

Bee 100 

Wasp 110 

Humming-bird moth (Macvo^Lossti) . 72 

Dragon-fly . . . 28 

Butterfly (Pontia Rupee) ... 9 

Synchronism of the action of the tiro wiinjs. By holding the 
insect in a suitable position we can make both wings rub on 
the cylinder at the same time. It is then seen, on the 
tracing, that the two wings act simultaneously, and that both 
perform the same number of movemeu s. Independently of 
this, we may easily convince ourselves lhat there must neces- 
sarily be a similar motion in both wings. 

If we move one of the wings of an insect recently killed, 
we shall find that a similar movement is given, in a certain 
degree, to the other corresponding wing ; if we extend one 
wing laterally, the other is also extended, if we raise one up, 
the other rises. The wai-p is well suited for this experiment. 

Still, in captive flight, certain insects can perform great 
movements with one of their wings, while the other only exe- 
cutes slight vibrations. The dung-fly, for instance, usually 
affects this kind of alternate flight; when it is held with the 
forceps, its two Avings ruiely move together. The sudden- 
ness and the unforeseen condition of these alternations, and 
the violent deviations which they give to the axis of the body, 
have prevented us from taking the simultaneous tracings of 
the movement of its two wings, and from ascertaining whether 
ihe synchronism continues under these conditions, in SJ ite of 
the unequal amplitude of the movements. 

The preceding figures show the regular periodicity of the 
movements of insect flight, biit they also prove that the 
graphic method cannot represent the whole course of the wing, 
for this organ can only be tangential to a certain portion of 
the surface of the cylinder. Whatever may be the movements 


which the wing describes, its point evidently moves on the 
surface of a sphere, the radius of which is the length of ihe 
wing, and the centre at the point of attachment of this organ 
with the niesolliorax. But a sphere can only touch a pi. me or 
convex surface at one point ; thus, we only olitain a number 
of points for a series of revolutions of the wing, if the turn- 
ing cylinder be only tangential to the extremity of the wing. 
More complicated tracings can only be obtained by more 
extensive contacts, in which the wing bends, and thus rubs 
a, portion of its surfaces or its edges on the blackened paper. 

We will explain the means by which the graphic method 
can serve to determine the movements of the wing, but let 
us first show the results obtained by another method, in 
order to render the explanation more clear. 

2. Ojitical method of the determination of the inurements of 
the uing. Having being convinced by the former experi- 
ments, of the regular periodicity of these movements, we have 
thought it possible to determine their nature by the eye. In 
fact, if we can attach a brilliant spot to the extremity of the 
wing, this spot passing continually through the same space 
would leave a luminous trace which would produce a figure 
completely regular, and free from the deformity incident to 
that effected by the friction on the cylinder. This optical 
method has already been employed for a similar purpose by 
Wheatetone, who placed brilliant metallic balls on rods pro- 
ducing complex vibrations, and thus obtained luminous 
figures varying according to the different combinations of the 
vibrating movements. 

By fixing a small piece of gold-leaf at the extremity of the 
wing of a wasp, and throwing upon it a ray of the sun while 
the insect was executing tin; movements of flight, we have 
obtained a brilliant image of the successive positions of iho 
wing, which gave i.e.uly the appearance represented iu 
fig. 71. 

This figure shows that the point of the wing descvil es a 
very elongated figure 8; sometimes, indeed, the wing sn 
to move entirely in one plane, and the instant afterwards the 
terminal loops which form the 8 are seen to open more ami 
more. When the opening becomes very large, one of the 



loops usually predominates over the other ; it is generally the 
lower one which increases while the upper diminishes. Indeed, 
by a still greater opening, the figure is occasionally trans- 
formed into an irregular ellipse, at the extremity of which MO 
can recognise a vestige of the second loop. 

Fio. 7 

wii ., 

71. Appearance of a wasp, the extremity of each of w 
ings has been gilded. 'Jhc insect is supposed to be place 

who ;o liwg -T 
:d ill a sun- 

We thought that we had been the first to point out the form 
of the trajectory of the wing of the insect, but Dr. J. B. Petti- 
grew, an English author, informs us th-it he had already 
mentioned this figure of 8 appearance described by the wing, 
and had represented it in the plates of his work.* It will 
be seen presently that, notwithstanding this apparent agree- 
ment, our theory and that of Dr. Pettigrew differ materially 
from each other. 

Changes of the plane of the iriiifj. The luminous appearance 
given during flight by the gilded wing of an insect, shows 

* On the Mechanical Appliances by which Flight is Maintained in the 
Animal Kingdom. Transact, of Linnean Society, 1S67,. p. 233. 


besides, that during the alternate movements of flight, tl.c 
plane of tlie wing changes its inclination with respect to the 
axis of the insect's body, and that the upper surface of the 
wing turns a little backward during the period of ascent, 
whilst it is inclined forward a little during its descent. 

If we gild a large portion of the upper surface of a wasp's 
wing, taking precautions that the gold-leaf should be limited 
to this surface only, we see that the animal, placed in the sun's 
rays, gives the figure of 8 with a very unequal intensity in 
the two halves of the image, as represented in fig. 71. The 
figure printed thus H gives an idea of the form which is then 
produced, if we consider the thick stroke of this character as 
corresponding with the more brilliant portion of the imago, 
nnd the thin stroke as representing the part which is less 

It is evident that the c;;use of the phenomenon is to be 
found in a change in the plane of the wing, and consequently 
in the incidence of the solar rays; being favourable to their 
reflection during the period of ascent, and unfavourable during 
the descent. If we turn the animal round, so as to observe 
the luminous figure in the opposite direction, the 8 will then 
present the unequal splendour of its two halvis, but in the 
inverse direction; it becomes bright in the portion before 
relatively obscure, and vice versa. 

We shall find in the employment of the graphic method, 
new proofs of changes in the plane of the wing during flight. 
This phenomenon is of great importance, for in it wo seem to 
find the proximate cause of the motive force which urges for- 
ward the body of the insect. 

In order to verify the preceding experiments, and to assure 
oui selves still more of the reality of the displacement of the 
wing, which the optical method has revealed to us, we have 
introduced the extremity of a small pointer into the interior of 
the figure 8 described by the wing, and we have proved that 
in the middle of these loops there really exist free spaces of 
the form of a funnel, into which the pointer penetrates with- 
out meeting the wing, whilst, if we try to pass the intersection 
where the lines cross each other, the wing immediately strikes 
against the pointer, and the flight is interrupted. 


Graphic method employed for the determination of the move- 
ments of the tviiiff. The preceding experiments throw great light 
on the traces which we obtain by the friction of the insect's 
wing against the blackened cylinder. Although the figures 
thus produced are for the most part incomplete, we are able, 
by means of their scattered elements, to reconstruct the figure 
which has been shown by the optical method. 

It is to be remarked that without sensibly inter firing- with 
the movements of the wing, we can obtain (races of seven or 
eight millimetres when the wing- is rather long. The slight 
flexure to which the wing- is subjected allows it to remain in 
contact with the cylinder to that extent ; we thus obtain a 
partial tracing of the movement ; so that if we are careful to 
produce the contact of the wing with the cylinder in different 
parts of the course passed through by the limb, we obtain a 
series of partial tracings which are complementary to each 
other, and thus allow us to deduce from them the form of a 
perfect curve of the revolution of a wing. Suppose, then, 
that in fig. 71, the curve described by the gilded wing is 
divided by horizontal lines into three zones : the upper one, 
formed by the upper loop ; that in the middle, comprehending 
the two branches of the 8, crossing each other and forming a 
sort of X ; the lower one including the lower loop. 

By registering the movement of the middle zone, we get 

Fio. 72. - -Tracinsr of the middle reyion of the course of the wing of a bee, 
showing the crossing of ihe two branches of the 8. One ol the branches 
is prolonged rai her far, but still the tracing of the lower loop has not been 

figures somewhat resembling each other, in which the lines, 
placed obliquely with respect to each other, cut ra-h other. 
This is the case in fig. 72, the middle region of the tracing 
of a bee, and in fig. 73, the middle portion of that of a 
humming-bird moth. 



The upper zone of the revolution of the wing jjives tracings 
analogous with that of fig. 74, in which t' e upper 'oops of I lie 
8 are plainly visiUe. The tracings of the zone which c< rre- 

Fm. ".'!. Tracing of the ini<l<ll> > -/.in- in tliu c..ur-c rtescribi .1 l.y tin- wit g of 
a humming-bird moth. Tlic numerous strokesot wl,k-h this tracing is 
formed, .-iris" fmni tho extremity of tho wing bein;i f ringed and present- 
ing a rough sti. face. 

spoiuls with the lower course of the wing give also loops like 
those of the upper arch (fig. 75 shows a specimen of them) ; 
so thnt the figure 8 of the tracing can lie reproduced l>y 

FlO. 74. Tins figure shows, in the tracing ni.-icle bj- a \v;is]>. tin 1 ii]'i T oop, 
aiicl all I he fxti lit oi' , in: 1 rani-h o the S. The niMillu part of tbis 
brnnclj is merely dut:e I liucaune of the feeble friction of the wing. 

bringing together the three fragments of its course successively 

If \vc could only once pi-mire the entire tracing formed by 
the wing of an ins-ret, we i-hould then get a figure identical 
with that which our learned writer on acoustics, Ko'iiig, was 
the first to obtain \\itli a \Vheatstone rod tuned to the octave, 
that is to say, describing an 8 in space. This typical form is 
represented in tiir. 70. We ^liall see that the graphic niet.hod 



is adapted to other experiments iutended to verify those which 
Me have already made l<y other means. By van ing- the inci- 
dence of the wing on the revolving cylinder, \ve cau foretell 
what will be the figure traced, if it be true lhat the 


r. ally d* scribes \hi i'oriu of au 8. Thus, if we obtaiu a figure 

Kio. To. Tracings of the wing of a wa<*p ; several of the lowi-r In V s r "'" 1 
dist.n -tly sjen Tliis traci'iir was nbtiiue'i by I'oldintr the insect sins 
to rub the cylinder by the hinder puint oi the wing, which gives very ex- 
ten' led curves 

conformable to that which we have foreseen, it will be an 
evident proof of the reality of these movements. 

Fin. 7<t. Tracing of a Wheattone's kaleidophone rod, timed to the octave, 
that is to say. vihr itinsf twice transversely for each longitudinal vibration. 
(This figure is ta vCn from 14. Kceniar. ' The slackeirni,' speed of the 
cylinder producer an app;oxima ion of the cui ves towards, the end ot the 

Let us suppose that the wing of the insect, instead of 
touching the cylinder with its point, as we have seen just 
now, brushes it with one of its edges ; and let us admit for 
an instant that the 8 described by the wing is so lengthened 
that it departs but slightly from the plane passing through 
the vertical axis of this figure. If we press the wing slightly 
against the cylinder the contact will be continuous, mid the 
tracing uninterrupted ; but the figure obtained will no 
longer be an 8 , if the cjiinder be immovable it will be an 
arc of a circle, whose concavity will be turned towards the 
point of insertion of the wing, a point which will occupy pre- 
cisely the centre of the curve described. 



If the cylinder revolve, the figure will be spread out liki- 
the oscillation of a tuning-fork registered under the samo 
conditions, and wo shall obtain a tracing more or less ap- 
proaching in form to that which is represented in fig. 77. 



Miajty ji j 

Fio. 77.- -Tracing olrtained with the wine of a lice "spillatinp in a piano 
which is sensibly tangential to the generatrix ol tueru^. storing cylinders. 

Tliis form, which theory enables us to predict, is always 
produced when the plane in which the wing moves is tan- 
gential to the generatrix of the cylinder. 

Hut in examining these tracings we easily recognise chainjc* 
in the thickness of the stroke parts which appear to have been 
made by a grr.-ner or less friction of the wing <>n the cylin- 
der; we here find a ne\v and certain proof of the existence of 
a movement in the form of an 8, as we now propose to show 
by a synthetic method. 

Let us take a Wheatstone's rod tuned to the octave ; let us fix 
on it the wing of an insect as a style, and let us trace the vibra- 
tions which it executes. We shall obtain, if the cylinder be 
motionless, figures of 8 when the wing tone' cs the paper by 
its point applied perpendicularly to its surface ; and if the 
cylinder revolve, we shall have lengthened figures of 8. 

We may obtain, with a rod tuned to the octave, tracings 
identical with those given by the insect ; of which a proof is 
afforded by the comparison of the two following figures: 

L'lu. 7- Tracings nf a wnp ; the Insesl i- l> H *" tint its win- t..u.'hiH 
tlie cylinder b> it--> j'uiul, .mJ ti.icc^ i;oi.c;all,> Uje mver loi.ji ..f the a. 



The graphic method also furnishes us with the proof of 
changes in. the plane of the Aving of the insect during the 
various instants of its revolutions. 

FIG. 70. Tracings of a Whentstone rod tuned to the octave, furnished 
with the win^r of a wasp, and arranged so as to register especially the 
upper loop of the 8. 

Fig. 80 shows the tracing furnished by a wing of a hum- 
ming-bird moth, arranged so as to touch the cylinder with its 
posterior edge. Ey bringing the insect not too near, we can 
succeed in producing only intermittent contacts ; these take 
place at the moment when the wing describes that part of the 
loops of the 8 whose convexity is tangential to the cylinder. 
The contacts which occupy the upper half of the figure alter- 
nate with those occupying the lower half. It is .seen, besides, 
that it is not the same surface of the wing which produces 
these two kinds of friction. In fact, it is evident that the 

FIG. 80. Tracings of the movements of the wing of a humming-bird 
muth (luacroglossa) rubbing on the cylinder by its lower eclga. 

marks of the upper half, each formed of a series of oblique 
strokes, are produced by the contact of a fringed border, while 
the contacts of the lower part are produced by another portion 
(if the wing which presents a region unprovided with fringes, 
and leaves a whiter trace witli boundaries better defined. 


These changes of plane are only found in great movements 
of the wing. This is an important fact, for it will explain to 
us the method of their production. Fig. 81 was furnished 
like fig. 80 by the movements of the wing of a moth (mucro- 
glossu) ; but on account of its fatigue these movements had 
lost nearly all their amplitude. 

r r r r- r r r r r- t\;st r r r r ' 

Fio. 81.- -Trncitiff of th" wim; of :i fatigued nvieni'-riossa. The figure 8 i< 
no longer to be seen, but only ;i siuiplu pcii'lular osci.Uitiou. 

We see only in this figure a series of pcndular oscillations, 
showing that the wing merely rose and fell without changing 
its plane. The bright line which borders the ascending and 
upper parts of these curves is explained by the alternate 
flexions of the wing as it rubs upon the paper, and shows 
that the upper surface was rough, and left a distinct trace, 
while the lower surface presented no simil/ir roughness. 

3. IHn'ctioit of the movement of tlie winy. One more very 
important element is required to give us a complete knowledge 
of the movements which the insect's wing executes in its flight. 
The optical method, while it shows us all the points in the 
curve described by the gilded extremity of the wing, does not 
indicate the direction in which this revolution is accomplished ; 
whatever may be the direction in which the wing moves in its 
orbit, the luminous image which it it fiords must be always 
the same. 

A very simple method has furnished a solution of this now 
(juestion. Let fig. 82 be the luminous image furnished by 
the movements of tlie right wing of an insect. The direction 
of these movements which the eye cannot follow is indicated 
by arrows. 

To determine the direction of these movements, we take a 
small rod of polished glass and blacken it with the smoke of 
u wax taper; when holding the rod at right angles to the 
direction in which the \\ing moves, we present the blackened 


end to (), that is to say, in front of the lo\ver loop. We 
endeavour to pass this point iiito the interior of the course 
described by the wing ; but as soou as it enters this region, 
the rod receives a series of shocks from the wing, vhich rubs 
on its surface, and wipes off the soot which covered it. When 
we examine the surface of the glass, we see that the soot has 
been removed only on the upper part, which shows that at 
the point (</) of its course, the wing is descending. The 
same expeiiment being repeated in ('), that is to say, in the 
hinder part of the orbit of the wing, it is found that the rod 
lias been rubbed beneath ; so that the wing at a was ascending. 
In the same manner it may be shown that the wing rises at 
b and descends al I'. 

Fio. S'2 Detcrtu'nation of the direction of the movements of ;:n iutect's 


We now know all the movements executed by an insect's wing 
during its revolution, as well as the double change of plane which 
accompanies them. The knowledge of this change of plane 
was given to us by the unequal brightness of the two branches 
of the luminous 8. Thus we may feel assured that in the 
course of ihe descending wing, that is from b' to a in fig. 82, 
the upper surface of the wing turns slighlly forward, while 
from a to b, that is, in ascending, this surface turns a little 





Causes of tin- movements .if the wihgs of insects The muscles only give 
a motion to and fro, the resistance of the air modifies the course of 
the wing Artificial representation of the movements of the insect's 
wing Of the propulsive effect of the wings of insects Construc- 
tion of an artificial insect which moves horizontally Change in the 
plane in flight. 

1. Causes of the movements of the win/j. These exceedingly 
complicated movements would induce us to suppose that there 
exists in insects a very co-nplex muscular apparatus, but 
anatomy does not reveal to us muscles capable of giving rise 
to all these movements. We scarcely find any but elevating 
and depressing forces in the muscles which move the wing ; 
besides this, when we examine more closely the mechanical 
conditions of the flight of the insect, we see that an upward 
and downward motion given by the muscles is sufficient to pro- 
duce all these successive acts, so well co-ordinated with each 
other ; the resistance of the air effecting all the other move- 

If we take off the wing of an insect (fig. 83), and holding 
it by the small joint which connects it with the thorax, expose 
it to a current of air, we see that the plane of the wing is 

Fio !xi - Structuiu "f :in inst'.'t'.s wing. 

inclined more and more as it is subjected to a more powerful 
impulse of the wind. The anterior nervure resists, but the 
membranous portion which is prolonged behind bends on 
in count of its greiiter pliancy. If we blow upon the upper sur- 


face of the wing, we see this surface carried backward?, while 
by blowing on it from beneath, we turn the upper surface 
forwards. In certain species of insects, according to Felix 
Plateau, the wing resists the pressure of the air acting from 
below upwards, more than that exerted in an opposite 

Is it not evident, that in the movements which take place 
during flight, the resistance of the air will produce upon the 
plane of the wing the same effects as the currents of air which 
we have just employed ? The changes in the plane, caused 
by the resistance of the air under these conditions, are pre- 
cisely those which are observed in flight. We have seen that 
the descending wing presents its anterior surface forwards, 
which is explained by the resistance of the air acting from 
below upwards; while the ascending wing turns its upper sur- 
face backwards, because the resistance of the air acts upon it 
from above downwards. 

It is, therefore, not necessary to look for special muscular 
actions to produce changes in the plane of the wing ; these, 
in their turn, will give us the key to the oblique curvilinear 
movements which produce the figure of 8 course followed by 
the insect's wing. 

Let us return to fig. 82 : the wing which descends has at 
the same time a forward motion ; therefore, the inclination 
taken by the plane of the wing, under the influence of the 
resistance of the air, necessarily causes the oblique descent 
from If to a. An inclined plane which strikes on the air has 
a tendency to move in the direction of its own inclination. 

Let us suppose, then, that the wing only rises and falls by 
its muscular action ; the resistance of the air, by pressing on 
the plane of the wing, will force the organ to move forward 
while it is being lowered. But this deviation cannot be 
effected without the nervure being slightly bent. The force 
which causes the wing to deviate in a forward direction neces- 
sarily varies in intensity according to the rapidity with which 
the organ is depressed. Thus, when the wing towards the 
end of its descending course moves more slowly, we shall 
see the nervure, as it is bent with less force, bring the wing 
backwards in a curvilinear direction. Thus we explain 


naturally llie formation of the descending branch of the 8 
passed through by the wing. 

The same theory applies to the formation of the ascending 
branch of this figure. In short, a kind of pendular oscilla- 
tion executed by the uervure of the wing is sufficient, to- 
gether with the resistance of the air, to give rise to all the 
movements revealed to us by our experiments. 

2. Aiti/'nial representation of the movements of the insects whig. 
These theoretical deductions require experimental verifica- 
tion, in order that they may be thorough!}- borne out. We 
have succeeded in obtaining the following results : 

Let fig. 84 be an instrument, which, by means of a multi- 
plying wheel and a connecting rod, gives to a flexible shaft 
rapid to and fro movements in a vertical plane. Let us take 
a membrane similar to that in the wings of insects, and fix it 
to this shaft, which will then represent the main rib of the 
wing ; we shall see this contrivance execute all the move- 
ments which the wing of the insect describes in space. 

If we illuminate the extremity of this artificial wing, we 
shall see that its point describes the figure 8, like a real wing; 
we shall observe also that the plane of the wing changes 
twice during each revolution in the same manner as in tiie 
insect itself. But in the apparatus which we now employ, 
the movement communicated to the wing is only upwards 
and downwards. Were it not for the lesistance of the air, 
the wing would only rise and fall in a vertical plane ; all 
these complicated movements are due therefore only to the 
resistance presented by the air. Consequently, it is this 
which bends the main rib of the wing, turning it in a direc- 
tion perpendicular to the plane in which its oscillation is 

But if the wing be pushed aside from its main-rib at each 
of its alternate movements, it is evident that the air, acted 
upon by this wing, will receive nn impulse in an opposite 
direction ; that is to say, it will escape at the side of the 
flexible portion of the wing, and cause in this direction a 
current of air. It is seen, in figure 84, that a candle placed 
by the bide of the thin edge of the wing, is strongly blown 
by the current of air which is produced. In front of the wing, 



on the contrary, the air will he drawn forwards, so that the 
fl.-ime of another candle placed in front of the nerviire will lie 
strongly drawn towards it. 

Fin. 84. Artificial representation of the movements of an insect's wing. 

3. Of the propulsive action of the wings of insects. In the 
same manner as the squib moves in the opposite direction to 
the jet of flame which it throws out, the insect propels itself 
in the course opposed to the current of air produced by the 
movement of its wings. 

Each stroke of the wing acts on the air obliquely, and 
neutralizes its resistance, so that a horizontal force results, 


which impels tin- insect forwards. This resultant acts in the 
descent of the wing 1 , as well as iu its upward movement, so 
that each part of the oscill itiou of tin- wing lias ;n action 
favourable to the propulsion of the animal. 

An effect is produced analogous with that which takes place 
when an oar is used in the stern of a boat in the action of 
sculling. Each stroke of the oar, which presents an inclined 
plane to the resisting water, divides this resistance into two 
forces: one acts in a direction oppose, 1 to the motion of the 
oar, the other, in a direction perpendicular to that movement, 
and it is the latter which impels the boat. 

Most of the propellers which act in water overcome the 
resistance of the fluid l>y the action of an inclined plane. 
The tail of the fish produces a propulsion of this kind; that 
of the beaver does the same, with this difference, that it 
oscillates in a vertical plane. Even the screw may be con- 
sidered as an inclined plane, movement is continuous, 
and alwnvs in the same direction. 

FJO. 85 R '1'i'i.xuiituUciii cf thu chiiugus in the i>l.lne of the insert's wing. 

If we wish to represent the inclination of the plane of the 
wing at the different parts of fts course, we shall obtain 
fig. N.>, in which the arrows indicate the direction of the 
course, of (he wing, and the lines, whether dotted or full, 
show the inclination of its plane. 

After this, we need only show the figure traced by Dr. Pet- 
ti^-rew in his work on flight, to prove how far the ideas of 
tliis English writer differ from ours 

The trajectory of the wing is represented by l)r. 1'etti- 
grew by means of fig. SU. Four arrows indicate, according 
to this writer, the direction of movements in the different por- 


tions of this trajectory. These arrows are in the same 
direction, and this first fact is opposed to the experiment 
described in page 195, where we have investigated the direc- 
tion of the movement of the wing, and have f( und it pass in 
opposite directions in the two branches of the 8. In order to 
explain the form which he assigns to this trajectory, Dr. Pet- 
tigrew admits that in its passage from right to left, the wing 
describes by its thicker edge the thick branch of the 8, and tho 

FIG. 86. Trajectory of the wing. 

thin branch by its narrow edge. The crossing of the 8 there- 
fore would be formed by a complete reversal of the plane of 
the wing during one of the phases of its revolution. In fact, 
the author seems to perceive in this reversal of the plane, an 
action similar to that of a screw, of which the air would form. 
the nut. We will not dwell any longer on this theory, but 
we have deemed it necessary to bring it forward, in con- 
sequence of the appeal which has been made to us. 

4. Artificial representation of an insect's flight. In order to 
render the action of the wing and the effects of the resistance 
of the air more intelligible, we have made use of the following 
apparatus : 

Let fig. 87 represent two artificial wings composed of a rigid 
main-rib connected with a flexible membrane, composed of 
gold-beater's skin, strengthened by fine nervures of steel ; the 
plane of these wings is horizontal ; a system of bent levers 
raises or lowers them without giving them any lateral mo- 

The movement of the wings is caused by a little copper 
drum, in which the air is alternately condensed and rarefied 
by the action of a pump. The circular surfaces of this drum 








are formed of india-rubber membranes connected with the 
two wings by bent levers ; the air when compressed or rarefied 
gives to these flexible membranes powerful and rapid move- 
ments, which are transmitted to both wings at the same time. 

A horizontal tube, balanced by a counterpoise, allows the 
apparatus to turn upon a central axis, and serves at the same 
time to conduct the air into the drum, which produces the 
motion. This axis is formed of a kind of mercurial gaso- 
meter, which hermetically seals the air conduits, while it allows 
the instrument to turn freely in a horizontal plane. 

Thus arranged, the apparatus shows the mechanism by 
which the resistance of the air, combined with the movements 
of the wing, produces the propulsion of the insect. 

If we set in motion the wings of the artificial insect by 
means of the air-pump, we see the apparatus soon begin to 
revolve rapidly around its axis. The mechanism of the mo- 
tion of the insect is clearly illustrated by this experiment, 
entirely confirming the theories which we have deduced from 
optical and graphic analysis of the movements of the wing 
during flight. 

It may be asked whether the figure of 8 movements de- 
scribed by the wing of a captive insect are also produced when 
the creature flies. We have just seen that the bending of the 
main- rib is entirely due to the force which carries the insect 
forward when it has become free. We might therefore sup- 
pose that the main-rib of the wing does not yield to this force 
when the insect flies freely, and that the resulting horizontal 
force is shown only by the impulsion of the whole of the insect 

If, after having gilded the wing of the artificial insect, we 
look at the luminous image produced during its flight, we still 
see the figure of 8 remaining, provided the flight be not too 
rapid. In fact, this figure is modified by the movement of 
the apparatus ; it becomes more extended, and resembles the 
8 registered on a revolving cylinder, but it is not reduced to a 
simple pendular curve, which would be the case if the main- 
rib were always rigid. We can understand that this may be 
caused by the inertia of the apparatus, which cannot be 
affected by the variable movements which each stroke of the 


wing tends to bring to Lear upon it. The artificial insect, 
when once set in motion, is sometimes before, and at others 
behind the horizontal force developed by the wing : on this 
account the rib of the wing is forced to bend, because the 
mass to be moved does not obey instantaneously the resulting 
horizontal force which the wing derives from the resistance of 
the air. The same phenomenon must take place in the flight 
of a real insect. 

5. Plane of oscillation of an insect's iriiiy. The apparatus 
which has just been described does not yet give a perfect idea 
of the mechanism of insect flight. We have been compelled, 
for the sake of explaining the movements of the wing more 
easily, to suppose that its oscillation is made from above 
downwards ; that is to say, from the back of the insect towards 
its lower surface, Avhen lying horizontally in the air. 

But we need only observe the flight of certain insects, the 
common fly, for instance, and most of the other diptera, 
to see that the plane in which the wings move is not verti- 
cal, but, on the contrary, very nearly horizontal. This plane 
directs its upper surface somewhat forward, and therefore 
the main-rib of the wing corresponds with this surl'm-o. 
Consecpaeutly, it is from below upwards, and a little forward 
that the propulsion of the insect is effected. The greater part 
of the force exerted by the wing will be employed in sup- 
porting the insect against the action of its weight ; the rest of 
this impulse will carry it forward. 

By changing the inclination of the plane of oscillation of its 
wings, which can be done by moving the abdomen so as to 
displace the centre of gravity, the insect can, according to its 
wishes, increase the rapidity of its forward flight, lessen the 
speed acquired, retrograde, or dart toward the side. 

It is easily to be seen that, when a hymenopterous insect 
living at full speed, stops upon a flower, this insect directs the 
plane of the oscillation of its wings backwards with considi-r- 
al>lo force. 

Nothing is more variable, in fact, than the inclination of 
the plane in which the wings of different species of insects 

The diptera nppoar to us to have this plane of oscillation 












very nearly horizontal; in the hymenoptera, tlie wing moves 
in a plane of nearly 45, but vhe lepidoptera flap their wings 
almost vertically, after the manner of birds. 

In order to render the influence of the plane of oscilla- 
tion more evident, and to show that the force derived from the 
resistance of the air has the double effect of raising the in-< i-r 
and directing its course, we must arrange t\\e ji'ujht intd-min-nt 
in a peculiar manner. It, will be necessary, in the first place, 
to be able to change the plane of oscillation of the wings, 
winch is effected by placing the drum on a pivot at the ex- 
tremity of the horizontal tube, at the end of which it turns. 
To show the ascensional force which is developed in this new 
arrangement, the instrument must no longer be confined to a 
simple movement of rotation in the horizontal piano, but it 
must be able to oscillate in a vertical plane like the scale beam 
of a balance. 

Fig. 88 shows the new arrangement which we have given 
to the instrument in order to obtain this double result. 

In this modification of the apparatus, the air-pump which 
constitutes the moving force is retained ; as is also the turn- 
ing 1 column which moves in the mercurial gasometer. But 
above the disc which terminates this column at the upper end, 
is fixed a new joint, which allows the horizontully-bulauced 
tube at the end of which the artificial insect is placed, to 
oscillate in the vertical plane like a scale-beam. In order to 
establish a communication between the revolving column and 
the tube carrying the insect, we make use of a little india- 
rubber tube, sufficiently flexible not to interfere with the 
oscillatory movements of the apparatus. 

Oilier accessory modifications may be seen in fig. 88; one 
consists in employing a glass tube to convey the air from the 
pump which moves the in>i t ; ; the other in a change of the 
in-': lianism by which motion is imparted to the win^s. The 
most important alteration is the introduction of a joint \\hieh 
allows us to give every possible, inclination to the plane in 
\\ hivh the \\ ings oscillate. 

The apparalus bring arranged so that the counterpoise, 
having he"ii brought nearer to the point of suspension, does 
l:ot ixactly balance the weight of the insect, the latter is 


placed so that its wings may move in a horizontal plane, the 
main-rib being uppermost. Thus all the motive force is 
directed from below upwards, and as soon as the pump begins 
to act, we see the insect rise vertically. We can easily esti- 
mate the weight raised by the flapping of the wings, and as 
we can vary the weight of the insect by altering the position 
of the counterpoise, we can determine the effort which is 
developed according to the frequency or the amplitude of the 

By turning the insect half way round, so that its wings, 
still oscillating in a horizontal plane, should turn their main- 
rib downwards, we develop a descending vertical force which 
may be measured by removing the counterpoise to a greater 
or less distance, and causing it to be raised by the descent of 
the insect. 

If we adjust the plane of oscillation of the wings vertically, 
the insect turns horizontally round its point of support in 
the same manner as has been previously described and 
represented in tig. 87. 

Lastly, if we give to the plane of oscillation of the wings, 
the oblique position which it presents in the greater number 
of insects ; that is to say, so that the main-rib turns at once 
upwards and slightly forward, we see the insect rise against 
its own weight, and turn at the same time round the vertical 
axis ; in a word, the apparatus represents the double effect 
which is observed in a flying insect, which obtains from the 
stroke of its wings, both the force which sustains it in the 
air, and that which directs its course in space. 

The first of these forces is by far the more considerable ; 
thus, when an insect hovers over a flower, and we see it 
illuminated obliquely by the setting sun, we may satisfy our- 
selves that the plane of oscillation of its wings is nearly hori- 
zontal. This inclination must evidently be modified as soon 
as the insect wishes to dart off rapidly in any direction, but 
then the eye can scarcely follow it, and detect the change of 
plane, the existence of which we are compelled to admit by 
the theory and the experiments already detailed. 

A curious point of study would be the movements prepara- 


tory to fliglit. We speak not only of the spreading of the 
wings, which in the coleoptera precedes fliglit, a movement 
which is sometimes so slow as to bo easily observed, nor of 
the unfolding of the first pair of wings, as wasps do before 
they fly. Other insects, the diptera, turn their wings as on 
a pivot around its main-rib in a very remarkable manner, 
at the moment when the wings which were previously ex- 
tended on the back in the attitude of repose start outwards 
and forwards before they begin to fly. Flies, tipulo) and 
many other kinds, show this preparatory movement very clearly 
when the insect, being exhausted, has no longer any energy 
in its flight. We see the main-rib of the wing remain sen- 
sibly immovable, and around it turns the membranous portion 
whose free border is directed downwards. This position 
having been obtained, the insect has only to cause its wing 
to oscillate in an almost horizontal direction from backwards 
forwards, and from forwards backwards. If this motion as on 
a pivot did not exist, the wing Avould cut the air with its edge, 
and would be utterly incapable of producing flight. In other 
species, as in the agrion, a small dragon-fly, for instance, the 
four wings, during repose, are laid back to back one against 
the other above the abdomen of the animal. Their main- 
ribs are upwards, and keep their position when the wings pass 
downwards and forwards ; here no preparation for flight is 
necessary. In these insects, as in butterflies, the wing lias 
only to set itself in motion when the creature flies. 

It is interesting to follow throughout the series of insects 
the variations presented by the mechanism of flight. 

The confirmation of the theory just propounded is found iu 
the experiments which certain naturalists have made by 
means of vivisection. For the most interesting of these wo 
are indebted to Professor M. Giraud. All these experiments 
prove that the insect needs for the due function of fliglit a 
rigid main-rib and a flexible membrane. If we cover the. 
llexilile part of the \\ing with a coating which hardens as it 
dries, fliglit is prevented. We hinder it also by destroying 
the rij-iilitv of the anteiior nerune. 


If we only cut oil', on the nmtr.iry, a portion of tiie flexible 
membrane, parallel to its hinder edge, the power of flight 


is preserved, for tlie wing retains the conditions essential to 
this function namely, a rigid main-rib and a flexible sur- 
face. Lastly, in some species the combination of two wings 
is indispensable to flight; a kind of pseudo- elytron consti- 
tutes the nervure, and behind this is extended a membranous 
wing, which is locked in with the posterior border of the 
anterior one. This second wing does not present sufficient 
rigidity to enable it to strike the air with advantage, and in 
these insects flight is rendered impossible, if we cut off the 
false wing-case ; it is as if we had destroyed the main-rib of 
a perfect wing. 



Conformation of the bird with reference to flight Structure of the wing, 
its curves, its muscular apparatus Muscular force of the bird; 
rapidity of contraction of its muscles Form of the bird ; stable 
equilibrium ; conditions favourable to change of plane Proportion of 
the surface of the wings to the weight of the body in birds of different 

THE plan by which we have been guided in the study of 
insect flight must also be followed in investigating that of 
birds. It will be necessary to determine, by a delicate mode 
of analysis, the movements produced by the wing during 
flight ; from these movements we may draw a conclusion as 
to the resistance of the air which affords the bird a fulcrum 
on which to exert its force. Then, having propounded cer- 
tain theories respecting the mechanism of flight, the force 
required for the work effected by the bird, &c., we will under- 
take to represent these phenomena by means of artificial 
instruments, as we have already done with respect to insects. 
But, before we enter methodically on this study, it will be 
useful to prepare ourselves for it by some general observa- 
tions on the organization of the bird, the structure of its wings, 
the force of its muscular system, its conditions of equilibrium 
in the air, &c. 


Conformation (>f the bird. By the simple inspection of a 
bird's wing, it is easy to see that the im < -hanisia of its flight 
is altogether different from that of an insect. From the 
manner in which the leathers of its wing lie upon each other, 
it is evident that the re>istance of the air cau only act from 
below upwards, for in the opposite direction the air would 
force for itself an easy passage by bending the long barbs of 
the feathers, which would no longer sustain each other. This arrangement, so carefully de^-rilied by Prechlt,* 
lias caused persons to suppose that the wing only needed to 
oscillate in a vertical plane in order to sustain the weight of 
the bird, because the resistance of the air acting from be- 
low upwards is greater than that which it exerts iu the 
opposite direction. 

This writer has been wrong in basing on the inspection of 
the organ of tlight all the theory of its function. We shall find 
that experiment contradicts in the most decided manner these 
premature inductions. 

If we take a dead bird, and spread out its wings so as to 
place them in the position represented in tig. 89, we see that at 

FIG. SO. Various curves of the wini; of u binl at different point;; in its 


different points in its length, the wing presents very remark- 
able changes of plane. At the inner part, towards the body, 
the wing inclines considerably both downwards and back- 
wards, while near its extremity, it is horizontal and some- 
times slightly turned up, so that its under surface is directed 
.somewhat backward. 

Dr. Pettigrew thought that he roidd find in this curve a 
sin-face resembling a lelt-handed screw propeller; struck with 
the resemblance between ihe form of the wing and that of 
the >i TCW u-ed in navigation, he considered the wing of a 

* Untersncliungeii i\\-i 'l-u Flu.:; <K-i Vu^.-l. Bvo \ .. mi.i 1S40. 


bird as a screw of which, the air formed the nut. AVe do 
not think that we need refute such a theory. It is too evi- 
dent that the alternating type which belongs to every muscular 
movement cannot tend to produce the propulsive action of a 
screw ; for while we admit that the wing revolves on an axis, 
this rotation is confined to the fraction of a turn, and is fol- 
lowed by rotation in the opposite direction, which in a screw 
would entirely destroy the effect produced by the previous 
movement. And yet the English writer to whose ideas we 
refer has been so fully convinced of the truth of his theory 
that he lias wished to extend it to the whole animal kingdom. 
He proposes to refer locomotion in all its forms, whether 
terrestrial, aquatic, or aerial to the movements of a screw 
propeller. Let us only seek in the anatomical structure of 
the organs of flight the information which it can afford us ; 
that is to say, that which refers to the forces which the bird 
can develop iu flight, and the direction in which these forces 
are exerted. 

Comparative anatomy shows us in the wing of birds an 
analogue of the fore limb of mammals. The wing when 
reduced to its skeleton, presents, as in the human arm, the 
humerus, the two bones of the fore-arm, and a rudimentary 
hand, in which we still fiud metacarpal bones and phalanges. 
The muscles also present many analogies with those of the 
anterior limb of man ; some parts of these bear such a resem- 
blance both in appearance and in function, that they have 
been designated by the same name. 

In the wing of the bird, the most strongly developed muscles 
are those whose office it is to extend or bend the hand upon 
the fore-arm, the fore-arm on the humerus, and also to move 
the humerus, that is say, the whole arm, round the articula- 
tion of the shoulder. 

In the greater number of birds, especially of the larger 
lauds, the wing seems to remain always extended during flight. 
Thus, the extensor muscles of the different portions of this 
organ would serve to give this organ the position necessary 
for rendering flight possible, and for maintaining it in this posi- 
tion ; as to motive work, it would be executed by other muscles, 
much stronger than the preceding namely, the pectorals. 


All the anterior surface of the thorax of birds is occupied 
by powerful muscular masses, and especially by a large 
iiiuscle, which by its attachments to the sternum, to the ribs 
and the humerus, is analogous with the large pectoral musele 
in man and the mammals ; its office is evidently to lower the 
wing witli force and rapidity, and thus to gain from the air 
the fulcrum necessary to sustain, as well as to move the mass 
of the body. Underneath the large pectoral is found the- 
medium pectoral, whose action is to raise the wing. On the 
exterior, the small pectoral, acting as accessory to the large 
one, extends from the sternum to the humerus. 

Since the force of a muscle is in proportion to the volume 
of this organ, when we consider that these pectoral irmscles 
represent about one- sixth part of the whole weight of the 
bird, we shall immediately understand that the principal 
function of flight devolves on these powerful organs. 

BoVelli endeavoured to deduce from the volume of the pec- 
toral muscles the energy of which they are capable; he con- 
cluded that the force employed \>y the bird in flight was equal 
to 10,000 times its weight. We will not here refute the 
error of Borelli ; many others have undertaken to combat his 
notions, and have substituted for the calculations of the Italian 
physiologist others whose correctness it would be difficult to 
prove. Such great contradictions as are to be found in the 
different estimates formed of the muscular force of birds have 
arisen from the fact that these attempts at measurement were 

Navier, depending on calculations which were not based on 
experiment, considered himself authorized in admitting that 
birds develop enormous mechanical work : seventeen swallows 
would exert work equal to a horse-power. "As easy would it 
be," said M. Bertrand, facetiously, " to prove by calculation 
that birds could not fly a conclusion which would rather com- 
promise mathematics." 

l;< >iiles, we find that Cugniard Latour admitted, basing his 
assertion on theory, that the wing is lowered eight times more 
quickly than it rises. Experiment, however, pi'oves that the 
wing of the bird is raised more quickly than it descends. 

f tin iiiuxciiliii- h'K-f <>f .'In I'ifil. \Ve must at the 


present day measure mechanical force under the form of work. 
It is necessary for this purpose to know what resistance is 
met with by tbe wing at each instant of its movements, 
and the direction in. which it repels from it this resisting 

Such an estimate requires a previous knowledge of the 
resistance of air against surfaces of different curvature moving 
with various degrees of velocity ; it supposes at the same time 
that we know the movements of the wing as well as their 
velocity and direction at every instant. 

. This problem will perhaps be the last which we may hope 
to solve, but we may even now study from other points of 
view the force exerted by the muscles of the bird, and esti- 
mate some of its characteristics. 

Thus, we may obtain experimentally a measure of the maxi- 
mum effort which these muscles can exert. This measure may 
not really correspond with the real effort displayed in flight, 
but it may keep us from forming exaggerated estimates. 

If the calculations of Borelli, or even those of Navier were 
correct, we ought to find in the muscles of the bird a very 
considerable statical force. Experiments show, however, that 
these muscles do not seem capable of more energetic efforts 
than those of other animals. 

Experiment. Our first experiment was made upon a buz- 
zard. The creature being hoodwinked was stretched upon its 
back, with its wings held on the table by bags filled with 
small shot. The application of the hood plunges these birds 
into a sort of hypnotism, during which we can make any num- 
ber of experiments upon them, without their evincing any pain. 

We laid bare the great pectoral muscle and the humeral 
region, we placed a ligature on the artery, disarticulated the 
elbow-joint, and took away all the rest of the wing. A cord 
was fixed to the extremity of the humerus, and at the end of 
this cord was placed a scale-pan, into which small shot was 
poured. The trunk of the bird being rendered perfectly im- 
movable, we excited the muscle by means of interrupted in- 
duced currents ; while the artificial contraction was produced, 
an assistant poured into the pan the small shot, until the 
force of contraction 'of the muscle was counteracted. At this 


movement, the weight supported was 2 kilogrammes 380 
grammes (about 6 '3 8 Ibs. troy). 

If we take into account the unequal length of the arms of 
the lever, on the side of the power and that of the resistance, 
we find that the pectoral muscle had been able to produce a 
total effort of 12 kilogrammes 600 grammes (about 33'78 Ibs. 
troy), which would correspond with a traction of 1298 
grammes (3 - C6 Ibs. troy) for each square centimetre of the 
transverse section of the muscle. 

A pigeon placed under the same conditions has given, as its 
entire effort, a weight of 4860 grammes, which, according to 
the transverse section of its muscle, raised to 1400 grammes 
the effort which each muscular bundle could develop for every 
square centimetre of section. 

If we admit that the electrical action employed in these 
experiments to make the muscles contract, develops an effort 
less than that which is caused by the will, it is not less true 
that these estimates, which are less than those which we 
generally obtain in the muscles of mammals under the same 
conditions, do not authorize us in recognizing in the bird any 
special muscular power. 

Lastly, if we were to take into account in this estimate 
the laws of thermo -dynamics, we might affirm that the bird 
would not develop in flight a very especial amount of work. 

All work, in fact, can only be performed with a certain 
waste of substance, and if the act of flying involved a great 
expenditure of work, we ought to find a notable diminution 
of weight in a bird when it returns from a long flight. Nothing 
of this kind is observed. Persons who train carrier pigeons 
have given us information on this point, from which we gather 
that a bird which has traversed in a single flight a distance ot 
fifty leagues (which it seems to do without taking any food), 
weighs only a few grammes less than at its departure. It 
would be interesting to make these experiments again with 
giviter exactitude. 

Of the rnjiiility of the muscular actions of birds. One of the 
most striking peculiarities in the action of a bird's muscles 
is the extreme rapidity with which force is engendered in 
them. Among the different ^ cies ut animals \\ hose muscular 


acts we have determined, the bird is that which, after the 
insect, has given the most rapid movements. 

This rapidity is indispensable to flight. In fact, the wing 
when lowered, can meet with a sufficient resistance in the 
air only when it moves with great velocity. The resistance 
of the air against a plane surface which strikes upon it 
and repels it, evidently increases in the ratio of the square 
of the velocity with which this plane is displaced. It 
would be of no use for the bird to have energetic muscles, 
capable of effecting considerable work, if they could only 
give slow movements to the wing ; their force could not 
be exerted for want of resistance, and no work could be pro- 
duced. It is otherwise with terrestrial animals which run or 
creep on the ground, with a speed more or less rapid accord- 
ing to the nature of their muscles, but which in every case 
utilize their muscular force by means of the perfect resistance 
of the ground. The necessity of velocity in the movements 
of fishes has been already observed, since the water in which 
they swim resists more or less, according to the rapidity 
with which their tails or their fins act upon it. Thus the 
muscular action of fishes is rapid, but much less so than 
that of birds, which move in a medium far more yielding. 

In order to understand the rapid production of movements 
in the muscles of the bird, we must remember that these 
movements are connected with chemical action, produced in 
the very substance of the muscle, where they give rise, as in 
machines, to heat and motion. We must therefore admit 
that these actions are excited and propagated more readily 
in the muscles of birds than in those of any other species of 
animals. In the same manner the different kinds of powder 
used in war differ much from each other in the rapidity of 
their explosion, and consequently give very different velocities 
to the projectiles which they impel. 

Lastly, the form of movement presents in different species 
of birds peculiarities which we have already noticed. We 
have seen in Chapter VIII. how much the dimensions of the 
pectoral muscles vary according as the strokes of the wing are 
requii-ed to have much force or great extent ; therefore we 
shall not recur again to this subject. 


Form of the bird. All those who have studied the flight of 
birds have very properly paid great attention to the form of 
these creatures, as rendering them eminently adapted to flight. 
They have recognised in them perfect stable equilibrium in 
the aerial medium. They have thoroughly understood the 
part played by the large surfaces formed by the wings, which 
may sometimes act as a parachute, to produce a very slow 
descent; while at other times these surfaces glide through the 
air, and following the inclination of their plane, allow the 
bird to descend very obliquely, and even to rise, or to hover 
while keeping its wings immovable. Some observers have 
gone so far as to admit that certain species of birds play 
an entirely passive part in flight, and that giving up their 
wings to the impulse of the wind, they derive from it a force 
capable of carrying them in every direction, even against the 
wind. It seems to us interesting to discuss, in a lew words, 
this important question in the theory of flight. 

The stable equilibrium, of the bird lias been well explained ; 
there is nothing for us to add to the remarks which have been 
made on this subject. The wings are attached exactly at 
the highest part of the thorax, and consequently when the 
outstretched wings act upon the air as a fulcrum, all the 
weight of the body is placed below this surface of suspension. 
We know also that in the body itself, the lightest organs, the 
lungs and the air vessels, are in the upper part ; while 
the mass of the intestines, which is heavier, is lower; also 
that the thoracic muscles, which are so voluminous and heavy, 
occupy the lower part of the system. Thus the heaviest 
part is placed as low as possible beneath the point of sus- 

The bird, as it descends with its wings outspread, will thus 
present its ventral region downwards, without its being neces- 
Miry to make an effort to keep its equilibrium ; it will take 
this position passively, like a parachute set free in space, or 
like the shuttlecock when it falls upon the battledore. 

But this vertical descent is an exceptional case ; the bird 
which allows itself to fall is almost always impelled by some 
previous horizontal velocity; it therefore slides obliquely upon 
iJie air, us every light body of large surface docs whew placed 



tinder the conditions of stable equilibrium which we have 
just described. Mons. J. Pline has carefully studied the 
different krnds of sliding movement which may take place ; he 
has even represented them by means of small pieces of appa- 
ratus which imitate the insect or the bird when they fly 
without moving their wings. 

If we take a piece of paper of a square form, and fold it in 




JTO /"ilj 

FIG 90. R' presenting, on the left, a contrivance intended to imitate the 
hovering of birds; it is placed in equilibrium by two equal weights 
attached to the extremities of a wire which is fixed in the lower part of 
the angle formed by the folded paper. This piece of apparatus falls verti- 
cally, us shown by the successive positions of .the wire when attiched to 
the two weights. On the right is seen the fame contrivance connected 
with one we.ght only. Its fall is parabolic, as s-hown by the dotted 

tlie middle, so as to form a very obtuse angle (fig. 90) ; then, 
at the bottom of this angle, let us fix with a little wax a 
piece of wire attached to two masses of the same weight ; we 
shall have a system which will maintain stable equilibrium 
in the air. If the centre of gravity pass exactly through the 
centre of the figure, we shall see it descend vertically when 
we let it go, the convexity of its angle being directed down- 

If we take away one of the weights, so as to alter the 
position of the centre of gravity, the apparatus, instead of 
descending vertically, will follow an oblique trajectory, and 
will glide through the air with an accelerated motion (fig. 90, 
to the right). 



The trajectory passed through ly this little instrument will 
be situated in a vertical plane, if the two halves of the appa- 
ratus are perfectly symmetrical ; Imt if they are not, it will 
turn towards the side in which while it cuts the air it finds 
the greater resistance. These effects, which are easily un- 
derstood, are identical with those which the resistance of the 
rudder causes in the advancing motion of a ship. They can 
also be produced in a vertical direction ; so that the trajectory 
of the apparatus may be a curve with its concavity above or 
below, as the case may be. 

Every thin body which is curved tends to glide upon the 
air according to the direction of its own curvature. 

Fir, 91. We have turned liack tin, ri.'lit hand (Miner of the two pianos 
which furm theaiitflc. After a descent in a parabolic curve, the apparatus 
.-iLMin, as shown l>y the doited trajectory. 

If we turn back either the anterior or posterior edge of our 
little apparatus, we shall see it at a given moment of its 
descent rise in opposition to its own weight, but it will soon 
lose its upward movement (fig. 91). Let us consider what 
has taken place. 

So long as the paper descended with but slight rapidity, 
tin- effect of its curvature was not perceptible., because. the 
air resists surfaces only in the ratio of the velocity with which 
they move. But when the rapidity was sullicii ntly great, an 



effect was produced similar to that of a rudder, -which turned 
up the anterior extremity of the little apparatus, and gave it 
an ascending course. Immediately, the weight which was 
the generating force of its gliding movement through the air 
began to retard it ; in proportion as it rose, it lost its velo- 
city until it reached the point of rest. After that, a downward 
movement commenced, then an ascent in the opposite direc- 
tion, so that the paper descended to the ground by successive 

If we give the apparatus a slight concavity downwards, 
the opposite effect is produced; we see (fig. 92), at a certain 


FIG. 9-2. Tbe right hand comer of the pi me of the angle has been bent 
downwards. After a parabolic descent, the apparatus falls very rapidly 
in a perpendicular direction. 

moment, the trajectory turns abruptly downwards, and the 
falling body strikes the ground with considerable violence. In 
this second case, when the rudder-like effect is produced, the 
new direction has in its favour the weight which hastens the 
full of the little instrument, as in the former experiment it 
rendered the re- ascent more slow. 

We have dwelt upon these effects, because they often occur 
in the flight of birds. They are mentioned in the old treatises 
on falconrv. which describe the evolutions of birds used in 

* * 


hawking. Without going further back, we find in Iluber* the 
description of these curvilinear movements of falcons, to which 
they gave the name of passades, and which consisted of an 
oblique descent of the bird, followed by a re-ascent, which 
they called ressource (from the Latin, resurgere). " The bird," 
says Iluber, "carried forward by its own velocity, would dash 
itself against the ground, were it not that it exercises a cer- 
tain power which it possesses of stopping when at its utmost 
speed, and turning directly upwards to a sufficient height to 
enable it to make a second descent. This movement is able 
not only to arrest its descent, but also to carry it without any 
further effort, as high, as the level from which it started." 

Surely, there is some exaggeration in saying that the bird 
can rise, without any active effort, to the height from which 
it stooped; the resistance of the air must destroy a portion of 
the force which it had acquired during its descent, and which 
must be transformed into a rising impulse. We see, how- 
ever, that the phenomenon of the ressource has been noticed 
by many observers, and that it has been considered by them 
as, to a certain extent, a passive motion in which the bird 
has to employ no muscular force. 

The act of hovering presents, in certain cases, a great ana- 
logy with the phenomena just described. When a bird a 
pigeon, fur example has traversed a certain distance by flap- 
ping its wings, we see it suspend all these movements for 
some instants, and glide on either horizontally, ascending or 
descending. The latter kind of hovering motion is that which 
is of longest duration ; in fact, it is only an extremely slow 
fall, but in which the weight assists the movement, while 
it checks it in the horizontal or ascending course. la the last 
two forms, the wing, directed more or less obliquely, derives 
its point of resistance from the air, like the child's plaything 
called a kite, but with this difference, that the vi-lnrity is 
given to the kite by the tractile force exerted on the string 
when the air is calm, while the bird when it hovers utilizes 
the speed which it has already acquired, either by its oblique 
fall or by the previous flapping of its wings. 

We have already said, that observers had admitted that 

* 8vo. (iclirva, 1784. 


certain birds which they called " sailing birds " could sustain 
and direct themselves in the air solely by the action of the 
wind. This theory has all the appearance of a paradox ; we 
cannot understand how the bird, when in the wind, and using 
no exertion, should not be affected by its force. 

If the 2)fissades, or the changes which it effects in the plane 
of its wings, can sometimes carry it in a direction con- 
trary to that of the wind, these can be only transient effects, 
compensated afterwards by a greater force driving them 
before the wind. 

Nevertheless, this theory of sailing flight has been advo- 
cated with great talent by certain observers, and especially by 
Count d'Esterno, the author of a remarkable memoir on the 
flight of birds. 

"Everyone," says this author, "must have seen certain 
birds practise this kind of sailing flight ; to deny it, is to 
contradict evidence." 

We know so little yet of the resistance of the air, especially 
with reference to the resolution of this force when it acts 
against inclined planes under different angles, that it is im- 
possible to decide on this question as to sailing flight. It 
would be rash absolutely to condemn the opinion of observers, 
by depending on a theory or on notions as vague as those 
which we possess on this subject. 

Ratio of the surface of the wings to the ii-eight of the body. 
One of the most interesting points in the conformation of birds 
consists in the determination of the ratio borne by the surface 
of the wings to the weight of the bird. Is there a constant 
relation between these two quantities ? This question has 
been the cause of many controversies. 

It has already been shown that, if we compare birds of 
different species and of equal weight, we may find that some 
have their wings two, three, or four times more extended 
than the others. The birds with large wing surfaces are 
those which usually give themselves up to a kind of hovering 
flight, and have been called sailing birds ; while those whose 
wing is short or narrow are more usually accustomed to a 
flight which resembles rowing. If we compare together 
two "rowing" or two "sailing" birds; if, to be more 



exact, we choose them from the same family, in order to have 
no difference between them except that of size, we shall find 
a tolerably constant ratio between the weight of these birds 
and the surface of their wings. But the determination of this 
ratio must be based upon certain considerations which have 
been long disregarded by naturalists. 

Mons. de Lucy has endeavoured to compare the surface of 
the wings with the weight of the body in all flying animals. 
Then, in order to establish a common unit between creatures 
of such different species and size, he referred all these esti- 
mates to an ideal type, the weight of which was always one 
kilogramme. Thus, having ascertained that the gnat, which 
weighs three milligrammes, possesses wings of thirty square 
millimetres of surface, he concluded that in the gnat type 
each kilogramme of the animal was supported by an alar sur- 
face of ten square millimetres. 

Having drawn up a comparative table of measurements 
taken in animals of a great number of different species 
and sizes, Mons. de Lucy has arrived at the following re- 
sults : 


W.i^ht of Animal. 

Surface of Wings. 

Surface per 

Kilogram mi'. 

Jlnat . 

3 miller. 

30 sq. inillim. 

10 sq. millim. 


20 center. 
290 graiiinirs. 

750 sq. centim. 

83 ,, 
2586 sq. centim. 





Australian Crane. 

9500 ,, 



From these measurements we obtain the following im- 
portant consideration, that animals of large size and great 
weight sustain themselves in the air with a much less pro- 
portionate surface of wing than those of smaller size. 

Such a result plainly shows that the part played by the 
wing in flight is not merely passive, for a sail or a parachute 
ought always to have a surface in proportion to the weight 
which it has to support ; but, on the contrary, when con- 
sidered in its proper point of vie\v, as an organ which strikes 
the air, the wing of the bird ought, as we shall see, to pre- 


sent a surface relatively less in birds of large size and of 
great weight. 

The surprise which we feel at the result obtained by Mons. 
de Lucy disappears when we consider that there is a geome- 
trical reason why the surface of the wing cannot increase in 
the ratio of the weight of the bird. In fact, if we take t\vo 
objects of the same form two cubes, for example one of 
which has a diameter twice as large as the other, each of the 
surfaces of the larger cube will be four times as large as that 
of the smaller one, but the weight of the large cube will be 
eight times that of the small one. 

Thus, for all similar geometrical solids, the linear dimen- 
sions being in a certain ratio, the surfaces will increase in 
proportion to their squares, and the weights in that of their 
cubes. Two birds similar in form, one of which has an 
extent of wing twice as large as the other, will have wing 
surfaces in the proportion of one to four, and weights in that 
of one to eight. 

Dr. Hureau de Villeneuve, basing his enquiries on these 
considerations, has determined the surface of wing which 
would enable a bat having the weight of a man to fly ; and 
he has found that each of the wings need not be three metres 
in length. 

In a remarkable work on the relative extent of wing and 
weight of pectoral muscles in different species of flying ver- 
tebrate animals,* Hartiugs shows that in a series of birds we 
can establish a certain relation between the surface of the 
wing and the weight of the body. But we must be careful 
only to compare elements which admit of comparison; for 
instance, the length of the wings, the square roots of their 
surfaces, and the cube roots of the weights of different birds. 

Let I be the length of the wing ; a, its area or surface ; 
and p the weight of the body ; we can compare together I, >/, 
and <\/p. 

Making observations on different types of birds, Hartings 
ascertained their measurements and weights, from which he 
obtained the following table : 

* Archives Neerlandaises, Vol. XIV., p. 1869. 



Name of Species. 









1. Larus ai'^ciitatus . 




_'. Anas nynira. . . 




3. Fulii-a atra . . 



2 05 

4. Alias rivrra . . . 




5. Lams ridlbandus . . 




6. Marlidrs JiULTIiaX . . 




7. Ilalius aquatu-us . . 




8. Turdus pilaris . . . 

1 (i:3-4 



9. Turdus miTiila . . 

88 8 



10. Sturnus vuljjaris . . 




11. Bombicilla garrula . . 



1 <;<) 

12. Alauda arveiisis. . . 




13. Parus major . . . 




14. Friugilla spinus . . 



2 33 

15. Parus coeruleus 




To this list of Hartings we will add another which we have 
prepared by the same method (p. 225). All the experiments have 
been made on birds killed by the gun, and a few instants after 
death. We have taken the surface of the two wings instead 
of only one, as Hartings had done ; this modification, which 
appeared necessary, is the principal cause of the difference 
which the reader will find between our numbers and those of 
the Dutch physiologist. To compare the two tables, it will 
be necessary to multiply by \/2 the number obtained by 

Hartings as the expression of the ratio -p 

The variations that we find in the ratio of the weight of 
the body to the surface of the wings in different species of 
birds, depends in a great degree on the form of the wings. 
In fact, it is not immaterial whether the surface which strikes 
the air has its maximum near the body or near the extremity; 
these two points have very different velocities. For an equal 
extent of surface the resistance will be greater at the point of 
the \\ing than at its base. It follows from this, that two birds 
of unequal suii'ai n of wing may find in the air an equal resist- 
ance, provided that these surfaces are differently arranged. 

The weight of the pectoral muscles is, on the contrary, in 
a Minplc rat in to tin- total weight of the bird, and imtwiih- 


standing variations which correspond with the different apti- 
tudes for flight with which each species is endowed, we find 
that it is about one- sixth of the whole weight in 
number of birds. 

the greater 

Surface of 

Name of Species. 

"\Veiglit = p. 

Wings = la. 
Square centi- 

Ratio = ^ 



Vultiir . 




Viiltur cinercns . . . 




Falco tiununculus 




,, ,, minor . 




Falco Kobi'.k 




Falco sublatio i?) . . . 




Falco palustris . 




Falco milvns . . 




Strix passerina . 




> 99 ' * "" 




Saxinola CBiiantlie 




Alauda cristata 




Corvus cornix . 




Upupa epops 




Merops apiastcr. 




Alceilo ispula . . . 



3 769 

Alccdo afra (?) . 




Columba vin;icea . . . 




Vanellus spinosus 




(Jlareola . . . 




Butco vulgnris . 




1'erdix cinerca . . . 




Sturnus vulgaris 




Corvus pica . . . . 




) > y t * * " 

275 00 



Hirundo urbk-a . . . 




Turdus merula . 




In conclusion, each animal which sustains itself in the air 
must develop work proportionate to its weight ; it ought, for 
this purpose, to possess muscular mass in proportion to this 
weight ; for, as we have already seen, if the actions performed 
by the muscles of birds are always of the same nature, these 
actions and the work which they perform will be in proportion 
to the mass of the muscles. 


But how is it that \\ings whose surfaces vary as to the 
square of their linear dimensions are sufficient to move the 
weights of birds which vary in the ratio of the cubes of these 

It can be proved that, if the strokes of the wing were as 
frequent in large as in small birds, each stroke woiild have a 
velocity whose value would increase with the size of the bird; 
and as the resistance of the air increases for each element of 
the surface of the wing, according to the square of the velo- 
city of that organ, a considerable advantage would result to 
the bird of large size, as to the work produced upon the air. 

Hence it follows, that it would not be necessary for large 
birds to give such frequent strokes of the wing in order to 
sustain themselves as would be required for those of smaller 

Observers have not, hitherto, been able to determine very 
accurately the number of the strokes of the wing, in order to 
ascertain whether their frequency is in an exact inverse ratio 
to the size of birds ; but it is easy to see that the number of 
strokes varies in birds of different size in a proportion of this 



Frequency of the movements of the wing Relative durations of its rise 
and fall Electrical determination Myographical determination. 

Trajectory of the bird's wing dining flight Construction of the instru- 
ments which register this movement Experiment Elliptical figure 
of the trajectory of the point of the wing. 

IN the general remarks on the form of the bird, and on the 
deductions to be drawn from it, the reader must have sec u 
that many hypotheses await experimental demonstration. For 
this reason, we have been anxious to apply to the flights of 


the Lird the method which has enabled us to analyse the other 
modes of locomotion. 

Frequency of the strokes of the wing. The graphic method 
which enuliled us so easily to determine the frequency of the 
strokes of the insect's wing cannot be employed under the same 
conditions when we experiment on the bird. It will be neces- 
sary to transmit signals between the bird as it flies and the 
registering apparatus. We have here to deal with a problem 
similar to that which we solved with respect to terrestrial 
locomotion, when we registered the number and the relative 
duration of the pressures of the feet upon the ground. We 
must now estimate the duration of the impacts of the wing 
upon the air, and the time which it occupies in its rising 

Electrical method. We made use at first of the electric 
telegraph. The experiments .consist in placing on the ex- 
tremity of the wing a kind of apparatus which breaks or closes 
an electric circuit at each of the alternate movements which 
it is induced to make. In this circuit is placed an electro- 
magnetic arrangement which writes upon a revolving cylinder. 
Figure 94 shows this mode of telegraphy applied to the study 
of a pigeon's flight, simultaneously with the transmission of 
signals of another kind, to be hereafter described. In this 
fiyure the two conducting wires are separated from each other. 

The writing point will trace a wavy line, the elevations and 
depressions of which will correspond with, each change in the 
direction of the movement of the wing. In order that the 
bird may fly as freely as possible, a thin flexible cable, con- 
taining two conducting wires, establishes a communication 
between the bird and the telegraphic tracing point. The two 
ends of the wires are fastened to a very small light instrument 
which acts like a valve under the influence of the resistance of 
the air. When the wing rises, the valve opens, the current 
is broken, and the line of the telegraphic tracing rises. When 
the wing descends, the valve closes, the current closes at the 
same time, and the tracing made by the telegraph is lowered. 

This instrument, when applied to different kinds of birds, 
enables us to ascertain the frequency peculiar to the move- 
ments of each. The number of species which we have been 



nblo to study is very small as yet ; the following arc tlio 
results obtained : 

Sparrow . 
Wild duck 

M"iir bux7;ir.l owl . 

Revolutions of wing 

]u r second. 





The frequency of the strokes of the wing varies also, according 
as the- liird is first starting, in full flight, or at the end of its 
flight. Some birds, as we know, keep their wings perfectly 
still for a time ; they glide upou the air, making use of the 
velocity already acquired. 

Relative duration of the depression and elevation of the wing 
r'uiitrary to the opinion entertained by some writers, the 
duration of the depression of the wing is usually longer than 
that of its rise. The inequality of these two periods is more 
distinctly seen in birds whose wings have a large surface, and 
which beat slowly. Thus, while tho durations are almost 
equal in the duck, whose wings are very narrow, they are 
imi>qu;il in the pigeon, and still more so in the buzzard. 
The follow ing are the results of our experiments : 

Total duration of a 
revolution of the wing. 




1 1 hundreds of a second 



hu't'on . . 




liuz/anl . 




1 1 is more difficult than would have been expected, to determine 
the praise instant when the direction of the line traced by the 
1 1 ',(- i-.-i nh changes. The periods during which the soft iron 
is lust attracted and then sot free, have an appreciable duration 
\\li u the blackened cylinder turns with sullicient rapidity to 
i-iiable us to measure the rapid movements which are the 
subjects of this iiiijuiiy. The inflections of the line traced by 
the telegraph then become curves, the precise commencement 


of each of which it is difficult to discover. There is therefore 
some limit to the precision of the measurements which we can 
take by the electric method ; we can still, however, estimate 
by this means the duration of a movement with a tolerably 
accurate approximation. 

Myographic method. We have seen that a dilatation accom- 
panies the contraction of the muscles, and follows it thiough 
all its phases. A shortening 1 of the muscle, either rapid or 
slow, feeble or energetic, as the case may be, will therefore be 
accompanied by a lateral dilatation which will have similar 
characters of rapidity or intensity. At each depression of the 
wing of a bird, the large pectoral muscles will be subject to a 
dilatation which, it will be necessary to transmit to the re- 
gistering apparatus. 

We shall have recourse, for this purpose, to the apparatus 
which we have employed in determinations of the same kind, 
when treating of human locomotion. Some slight modifica- 
tions \\ill enable them to give signals of the alternate phases 
of dilatation and relaxation of the large p( ctoral muscle. 

Flo 93. Apparatus to investigate the contraction of the thoracic muscles 
of the bird. The upper convex surface is funned of a membrane of india- 
rubber supported by a spiral spring 1 ; this part is applied to the muscles. 
The lower surface, in contact: with the corset, carries four small houks 
which are fastened in the stuff and keep the instrument in its place. 

The bird flies in a space fifteen metres square and eight 
metres high. The registering apparatus being placed in the 
centre of the room where the experiment is made, twelve 
metres of india-rubber tubing are sufficient to establish a 
constant communication between the bird and the apparatus. 

A sort of corset is fixed on a pigeon (see figure 94). Under 
this corset, between the stuff, which is tightly stretched, and 



the pectoral muscles, a small instrument is slipped, which is 
intended to show the dilatation of the muscles, and is constructed 
in the following 1 manner: 

A little metal pan (fig. 93), containing within it a spiral 
spring, is closed by a membrane of india-rubber. This closed 
pan communicates with a tube transmitting air. 

FlO 94 I |>. liim-nl in d. 'termini' liy t'ic electrical nml . 

methods, :it tlio MIIIIC. time, tin- l'iv lUi'lii'V uf til'' movements of the wing 
and the rvl.itivc duration* uf its c'.evati m and deiires.siuu. 

Madi ]in ^siire on the india-rubber membrane depresses 
it, and the spring ^ives way; the air is driven out of the pan, 
and escapes by tin- tube. When the pressure ceases, the air 
is retiirnrd to the instrument by 1 lie elasticity of the spring 


which raises tlie membrane. Alternate outward and inward 
currents of ah- are thus established in the tube, and this 
movement transmits to the registering apparatus the signals 
of the less or greater pressures exerted on the membrane of 
the small pan. 

The registering instrument is the lever drum, with which 
the reader is already acquainted. It gives an ascending curve 
while the muscle contracts, and a descending one when it is 

Fig. 94 represents the general arrangement of the experi- 
ment, in which the electric telegraph and the transmission of 
air are used at the same time. 

It shows a pigeon fitted with a corset, under which is 
slipped the instrument which is to show the action of the 
pectoral muscles. The transmitting tube ends in a registering 
apparatus, which writes on a revolving cylinder. 

At the extremity of the pigeon's wing is the instrument 
which opens or closes an electric current, as the wing rises 
or sinks. The two wires of the circuit are represented as 
separated from one another ; within the circuit are seen two 
elements of Bunsen's pile, and the electro-magnet which, 
being furnished \\itli a lever, registers the telegraphic signals 
of the movements of the wing. 

Experiment. The bird is set free at one extremity of the 
room, the dove-cot in which it is usually kept being placed 
at the opposite end. The bird as it flies naturally seeks its 
nest in which to rest. During its flight we obtain the tracings 
represented by fig. 95. 

It is seen that the tracings differ according to the kind of 
bird on which the experiment is made. However, we ob- 
serve in each of the tracings the periodical return of the two 
movements a and b, which are produced at each revolution of 
the wing. 

On what do these two muscular acts depend ? It is easy 
to discover that the undulation a corresponds with the muscle 
that elevates the wing, and b with that which depresses it. 
This can be proved : first, by collecting, at the same- time as 
the muscular tracing, those of the ascending and descending 
movements of the wing transmitted by electricity. "NY lieu 


these two tracings are placed over each other, they show that 
the time of the elevation of the wing agrees with the dura- 
lion of the undulation a, and the time of its depression coin- 
cides with the undulation b. 

From this we may see how the undulations a and b are 
produced in all the muscular tracings obtained from birds. 
la fact, close by the portion of the bird's breast on which the 
experiment is made, and near the projecting edge of the 
sternum, there are two distinct layers of muscle; the more 
superficial one is formed by the large pectoral, the depressor 
of the wing ; the deeper one by the middle pectoral, or ele- 
vator of the wing, whose tendon passes behind the forked 
part of the sternum to attach itself to the head of the 

These two muscles, being superposed, will act by their 
dilatation on the apparatus applied to them ; the elevator of 
the wing, swelling as it contracts, gives its signal by the un- 
dulation a ; the great pectoral signals the depression of the 
wing by the undulation b. 

We may verify the correctness of this explanation by means 
of a very simple experiment. Anatomy shows us that the 
muscle which elevates the wing is narrow, and only covers the 
depressor in its most inward part, situated along the ridge 
of the sternum ; so that if we displace the little apparatus 
which shows the movement of the muscles, and remove it a 
little outwards, it will occupy a part where the depressor of 
the wing is not covered by the elevator, and the tracing 
Avill only present a simple undulation, corresponding with 
b in the curves of fig. 95. It is thus plainly shown that the 
undulations a and b in the muscular tracings of the birds on 
which we have experimented correspond exactly with the 
actions of the principal muscles which elevate and depress 
the wing ; but we cannot attach great importance to the form 
of the tracings, in order to deduce from them the precise 
nature of the movement performed by the muscle. These 
movements seem, in fact, to encroach on each other ; so that 
the relaxation of the elevator of the wing is probably not 
completed when the depressor begins to act. 

We expect nothing more from these tracings than that 


i - 


which they more readily furnish ; 
namely, the number of the revolu- 
tions of the wing, the greater or less 
regularity of these movements, and 
the equality or inequ ility of each of 

Confining the question within 
these limits, experiment shows that 
the strokes of the bird's wing differ 
in amplitude and in frequency from 
one moment to another as they fly. 
When they first start, the strokes 
are rather fewer, but much more 
energetic ; they reach, after two or 
three strokes of the wing, a rhythm 
almost regular, which they lose 
again when they are about to settle 
(fig. 90). 


We have seen, when treating of 
the mechanism of insect flight, that 
the fundamental experiment was 
that which revealed tons the course 
of the point of the wing throughout 
each of its revolutions. Our know- 
ledge of the mechanism of flight 
naturally flowed, if we may so say, 
from this first notion. 

The same determination is equally 
necessary for the flight of birds ; 
but the optical method is unsuitable 
for this purpose. In fact, the move- 
ment of the bird's wing, although 
too rapid to be appreciable by the 

"M 1 . is not sufficiently so to furnish 
such a persistent impression on the 
retina as to show its whole course. 


The graphic method, with its transmission of signals, which 
we have hitherto employed, only furnishes llio expression, of 
movements which take place in. a straight line, such as the 
contraction or lengthening of a muscle, the vertical and hori- 
zontal oscillations of the body during Ihe act of walking, &c. 
It is only Ly combining this rectilinear movement with the 
uniform advance of the smoked surface that receives the 
tracing, that we obtain, the expression of the velocity with 
which the movement at each instant is effected. 

The action of the wing during flight docs not consist 
merely of alternate elevations and depressions. We have oidy 
to look at a bird as it ilies over our head to ascertain that the 
wing is carried also for\vard and backward at each stroke. 
From this double action must result a curve which it is neces- 
sary to describe. 

It can be geometrically shown that every plums figure, 
that is to say, every figure susceptible of being described upon 
a plane surface, be produced by the rectangular combina- 
tion of two rectilinear movements. The tracings obtained by 
Kocnig by arming with a style Wheatstone's vibrating rods, 
and the luminous figures of musical chords which Lissajous 
produced by the retlection of a pencil of light upon two 
mirrors vibrating perpendicularly to each oilier, are well- 
known examples of the formation of a plane figure by means 
of two rectilinear movements at light angles to each other. 

Thus, if we can transmit at the same time the movements 
of elevation and depression executed by the wing of the bird, 
as well as those which the organ makes forwards and back- 
wards; then, supposing that a tracing point can receive simul- 
taneously the impulse of these two movements at right angles 
to each other, this point will describe on the paper the exact 
tracing of the movements of the bird's wing. 

We have endeavoured first to construct an instrument which 
would thus transmit to a distance any movement whatever, 
and register it on a plane surface, without attending to the 
method by which this machine, which may be more or less 
heavy, might be adapted to the body of the bird. Fig. 97 
represents our first experimental instrument, the description 
of which is indispensable in order to enable our readers to 


understand tho construction of the machine which we finally 

On t\vo solid feet carrying vertical supports, we placed 
two horizontal arms parallel to each other. These were two 
aluminium levers, which, by means of the apparatus we are 
about to describe, will both execute the same movements. 
Kadi of these levers is mounted on a Cardan joint, that is to 
say, a universal joint which allows every kind of movement; 
so that each lever can be carried upwards, downwards, to 
the right or the left ; it can describe with its point the base 
of a cone of which, the Cardan forms the apex ; in fact it will 
execute any kind of movement which the experimenter may 
please to give it. 

It was requisite to effect the transmission of the move- 
ments of one of tliese levers to the other, and that at a dis- 
tance of ten or fifteen metres. This is done by a method with 
which the reader is already acquainted the employment of 
air-drums and tubes. 

The lever, which in fig. 97 is seen to the left hand, is 
fastened by a vertical metallic wire to the membrane of a 
drum placed underneath it. In the vertical movements of 
the lever, the membrane of the drum, alternately depressed 
and raised, will produce a current of air, which will be trans- 
mitted by a long air-tube to the membrane of a similar drum 
belonging to the apparatus on the right hand. The second 
diuiii, placed above the lever which corresponds with it, and 
is fastened to it, will faithfully transmit all the vertical 
movements which have been given to drum No. 1 (that on 
the lefi). The motion of tho two levers will be in the sumo 
direction, on account of the inversion of the position of the 

Let us suppose that we lower the lever No. 1 ; we com- 
press the membrane of the drum beneath it; a current of 
air is produced which r.iiM-s the membrane of the second 
drum, ami consequently lowers lever No. 2. On the contrary, 
the i.-v.itinn of Irver No. 1 will produce an inward current of 
air. which will rai^e (lie menl'iane and the le\vr of No. 2. 

I'mcn-ding in the same manner for the transmission of 

vi mcnts, in the hori/ontal plane, we place to the right of 



one of the levers and to the left of the others, a drum whose 
membrane, situated in the vertical plane, acts in a lateral 
direction; the transmission, of these movements is made by a 
special tube, as in the case of the vertical movements. 

The apparatus having been thus constructed, if \ve take in 
our fingers the extremity of one of the levers, and give it any 
motion whatever, we shall see the other lever repeat it with 
perfect fidelity. 

All the difference consists in a slight diminution of the am- 
plitude of the movements in the second lever. This is because 
the air contained in each of the systems of tubes and drums 
is slightly compressed, and consequently does not transmit 
completely the movement which it receives. It would be easy 
to remedy this inconvenience, if it were found to be one, by 
giving to the receiving apparatus a greater sensibility, which 
might be effected by placing the Cardan joint a little nearer 
the point where the movement is transmitted to Iho lever of 
(lie second instrument. But it is better not to seek to amplify 
the movements too much when we wish to register them by 
tracings, since we then augment the friction, and diminish the 
force by which it must be overcome. 

After having ascertained that the transmission of any move- 
ment whatever is effected ill a satisfactory manner by this ap- 
paratus, we sought for a means of tracing this movement on a 
plane surface. The difficulty which occurred in the application 
of the graphic method to the study of the movement of the 
insect's wing, again presents itself here ; but in this case there 
are no means of avoiding it by taking only partial tracings. 

The point of the lever No. 2 describes in space a spherical 
figure incapable of becoming tangential, except in a single 
point, to the smoked surface which is to receive the tracing. 
Consequently, it lias been necessary to register the projection 
of this figure on a plane surface, and to arrange the lever in 
such a manner that it may lengthen or shorten itself as re- 
quired, in order to keep always in contact with the smoked 
jj.ivs. This result was obtained by means of a spring which 
served a-; a writing point. 

Fig. 98 shows the spring in question, at the extremity of a 
I' r< r. It is \\ide at the base, in order to rctist any tendency 


to lateral deviations under the. influence of the friction ; this 
base is fixed to a vertical piece of aluminium, which is 
attached by its lower part to the extremity of the lever. In 
this manner, the point of the spring which acts as a style is 
considerably in front of the lever whose movements it is to 
register. Let us suppose the levtr to rise, and take the 
position indicated by the dotted line in figure 98 ; while 
traversing this space, it will have described an arc of a circle, 
and its extremity will no longer be in the same plane as before, 
but the elasticity of the spring will have carried the writing 
point more forward ; it will still continue, therefore, to be 

Fio. 98. Elastic point tracing on a smoked glass. 

in contact with the plane on which it is to trace. Thus the 
lever lengthens or shortens, as required, and its point 
always presses on the plane. The surface on which the tracing 
is received is a well-polished glass, and the spring which 
forms the style is so flexible, that the elastic pressure which it 
exerts upon the glass rubs it but slightly. 

The apparatus being thus arranged, it must be submitted 
to a verifying process, to ascertain if movements are faithfully 
transmitted and registered. 

For this purpose, arming the two levers of fig. 97 with 
similar styles, we placed their points against the same piece 
of smoked glass; we directed with the hand one of the levers 
so as to trace any figure, to sign one's name for instance ; the 
other lever ought to trace the same figure, to reproduce the 
same signature. 


It generally happens that the transmission is not equally 
easy in Loth directions ; we perceive a slight deformity iu the 
transmitted figure, which is lengthened more or less both in 
lieight and in width. This fault can al\va}-s be corrected; it 
arises from the fact, that the membrane of one of the drums, 
being more stretched than that of the other, obeys less easily. 
We soon succeed, by various trials, in giving the same sensi- 
bility to the t\vo membranes, which is ascertained, when we 
find that the figure traced by the first lever is identical with 
that of the second. 

l''.c]erii>ient to determine graphically the trajectory of the icing. 
The following are the modifications which allow us to apply 
this mode of transmission to the study of the movements of 
the wing of a flying bird. 

As the apparatus must necessarily be of considerable weight, 
we chose a large bird to carry it; strong full-grown buzzards 
were employed in these experiments. By means of a kind of 
corset which left both the wings and the legs at liberty, we fixed 
on the back of the bird a thin piece of light wood on which 
the apparatus was placed. 

In order that the lever mi^ht execute faithfully the same 
movements as the wing, it was necessary to place the Cardan 
joint of this lever in contact with the humeral articulation of 
the buxzard. Therefore, as the presence of the drums -by the 
side of the lever did not permit this immediate contact, we 
had recourse to a parallelogram, which transmitted to the lever 
of the apparatus the movements of a long rod, the centre of 
motion in which was very near the articulation of the bird's 
wing. Then, in order to obtain perfect correspondence be- 
tween the movements of the rod and those of the buzzard's 
\viug, we fixed on the outer edge of the wing that is to say, 
on the metacnrpal bone of the thumb of the bird, a very tight 
screw clip, furnished with a ring, through which slipped the 
steel rod, of which we have before spoken. 

Fig. 99 represents the buzzard flying with the apparatus 
just described ; underneath it hang the two transmitting tubes 
\\hich are fixed to the registering instrument. 

\lter a great many fruitless attempts and changes in the 
i nn.sliuctiun of (he. apparatus, which, being too fragile, broke 






at almost every ilight of the bird, \\c succeeded in 
satisfactory results. During- the whole of the bird's flight the 

registering lever descrilied a kind 
of ellipse. This ellipse, registered 
Hi a plate having an advancing' 
movement from right to left, gave 
ligure 100. In order to under- 
stand thistigure, wemust imagine 
the bird Hying from left to right 
(as the tracing 1 is to be read), 
and rubbing the extremity of its 
left wing against a wall blackened 
with smoke; the tracing which 
its wing would leave under these 
conditions would be identical with 
tliat represented iu fig. 100. 
This curve is a kind of ellipse 
spread out by the advancing mo- 
tion of the plate which receives 
the tracing. Except some trem- 
blings of the line, which arose 
from the imperfection of the 
apparatus, the trajectory of the 
bird's wing 1 may be compared to 
the tracing given under the same 
conditions by a Wheatstone'srod, 
tuned in unison, and giving- an 
elliptical vibration. 

Fig. 101 represents a tracing- 
of this kind. 

The determination of the course 
of the wing, with the different 
phases of its velocity, is so im- 
portant, that\\e resolved to verify 
liy various methods the reality 
<>i' this elliptical form. All our ex- 
periments have furnished results 
\\hicliugree v ith each other; they have shown that birds of dif- 
I. lent .-pri ies describe \\ith t heir wings an elliptical trajectory. 



D'Esterno had already determined by his experiments that 
this trajectory existed ; arid lie has even figured, in his work, 
the curve described ; but, in his opinion, the larger axis of 
the ellipse would be directed downwards and backwards, which 
is entirely opposed to the result of our experiments. 

FIG. 101. Ellipse formed V>y a WhentsVme's rod tuned in unison and 
tiuciiig o)i a revolving cylinder. 

We remark also the unequal amplitude of 'the strokes of 
the wing from the commencement to the end of fig. 100. 
This variation in size agrees \vith what we have already 
stated concerning fig. 96. This showed that at the com- 
mencement of its flight, the bird gives stronger strokes with 
its wing. It is at that moment, in fact, that it has to effect 
the maximum of work, in order to rise from the ground. 
After this, it will only need to remain at the height which it 
has attained. 




New determination of tlie trajectory of llio wing Description of apparatus 

Tninsiiiivsinii of a movement by the traction of a thread Instni- 
ment an-l ap aratus to suspend the bird Experiment on the flight of 
a pigeon An ilysis of the curves Description of the apparatus 
intended to give indications of the changes in the plane of the wing 
.luring flight Relation of these changes of plane with the other 
movements of the wing. 


THE simultaneous analysis of the changes in the plane of 
the wing, ami of the various phases of its course, would have 
presented great dilliculties, if we had not discovered a new 
arrangement of the apparatus, which allowed us to examine, 
at the same time, an, almost inliuite number of different 

This simplification of the incthod consists in the employ- 
ment of threads to transmit the movement of any point 
whatever to the experimental apparatus, which in its turn, 
bends it by the ordinary means to the registering instrument. 

Dcsci-ijitiuii of apparatus. Let fig. 102 bo two lever-drums 
connected together, similar to those already represented in 

iig. 21. 

The kver L belorys 1o the experimental apparatus, that on 
\\hichthemovernent to be studied is to act. On the frame 
of this first instrument let us place an arm of bent wire, from 
the extremity of which an india-rubber thread, F, will pass to 
tbe lever L. From the san.e lever hangs a cord of twisted 
silk, C C, to which is suspended a leaden ball. 

Let us suppose the ball to be at its lowest position at 
the point A the lever L occupies the place marked by a dotted 
line, while in the registering instrument the air driven out 
raises the lever L', which traces the movement. 


Now let us raise the ball to the position B ; the elasticity 
of the india-rubber thread will cause the lever to rise. Thus 
it is acted upon alternately by two forces, sometimes by the 
traction exerted by the silk thread, which lowers it ; at others, 
by the retraction of the india-rubber, which re-acts as soon as 
the tractile force ceases. Thus the lever will follow faithfully 
all the movements which are given to the extremity of the 
thread which draws it down. 

FIG. 10'2 Transmission of a to anrl-fro movement by means of a simple 


The lever I/, which is to trace on the cylinder the 
ments transmitted to it, moves in an opposite direction to the 
course of the cord C C. The tracing will thus be reversed, 
and if it were important to obtain it in the same direction, it 
would be necessary to turn the registering 1 drum, so as to place 
the membrane downwards.* 

With two instruments of this kind, one acted upon by th'e 

* As many instruments of this kind are required as there are move- 
ments to be studied. But three connected levers will always be sufficient 
to ascertain the movements of a point in space, since each of the posi- 
tions of this point is defined when it has been determined with reference 
to three axes at right angles to each other. 


vertical tractions of a thread attached to (.lie wing of tlio bird, 
and the other by the horizontal tractile force of a second 
thread also fastened to its wing, \ve can verify the experiment 
which has furnished us with the trajectory of this organ, and 
obtain \\ith much greater accuracy the curve illustrating its 
movements. This \ve have perfectly succeeded in doing, as 
we shall show further on. 

But this is not all that we wished to obtain. We might 
have made the bird carry the apparatus which we have just 
described, and put it in communication with the registers by 
means of tubes, as in the experiment represented in fig. 99. 
lint while seeking to render the analogies of the movements 
of flight perfect, we wished also to discover a plan which 
would be equally applicable to the living bird, and to every 
kind of machine intended to represent artificially aerial loco- 

In this project we must endeavour to copy Nature in her 
functions, as the artist does in her form. We must give more 
rapidity to movements which are too slow, and render those 
slower which are too rapid, until they have absolutely the same 
characters and the same mechanical effects as those of the 

This incessant comparison requires us to place ourselves 
under new conditions. Hitherto, our analytical studies have 
been directed to a bird flying at liberty ; for since we have 
never been able to imitate flight exactly by mechanical 
methods, it would be impossible to leave an artificial instru- 
ment to itself; it would be broken at each experiment. 

The comparison of the movements of tlio bird with those 
of imitative instruments does not require those movements to 
be effected under the conditions of free flight. Provided that 
the bird, although restrained in its movements, should flap 
its win^s with the intention of flying, wo shall bo able to 
study these muscular actions with reference to their characters 
of force, extent, and duration. A bird suspended by a cord 
and allowed to flap its wings might, for example, bo com- 
pared with an artificial apparatus suspended in the same 

Wo have tried a less imperfect mode of suspension which 


allows the Lird to fly under conditions almost normal, and 
at the same time will permit the artificial instruments to make 
attempts at flight, without any fear of letting them fall, if 
the movements which they produce should be insufficient to 
sustain them in the air. We will now describe this suspen- 
sory apparatus. 

There is a sort of frame-work of six or seven metres in 
diameter, in which the bird moves continuously, being thus 
able to furnish us with an observation of a circular flight of 
long duration. We give the instrument a large radius, that 
its curve, being less abrupt, should modify less the nature of 
the movement which the bird may make. Harnessed to some 
extent to the extremity of a long arm which turns on a central 
pivot, the bird ought to be as free as possible to go through 
its movements of vertical oscillation. We shall presently see 
that a bird passes through a double oscillatory movement in 
a vertical plane for each revolution of its wings. 

Arrangement of the frame. The conditions to be fulfilled are 
the following : in the first place, a great mobility of the 
instrument, that the bird may have the least possible resist- 
ance to overcome in its flight ; then, a perfect rigidity of the 
arm of the machine, to prevent any vibrations peculiar to 
itself, which might render unnatural the movements executed 
by the bird. 

Fig. 103 shows the general arrangement of the apparatus. 
A steel pivot, resting on a solidly-cast socket of great weight, 
is placed on the platform of a photographic table. This table 
is raised by means of rack-work, so that the operator, after 
having arranged his apparatus so as to suit the experiment, 
may place the platform sufficiently high for the instrument to 
turn freely above his head. 

The frame- work, properly so called, is a bow formed of a 
long piece of fir-wood slightly curved. The string of this 
bow is an iron wire, which is fixed by the middle to a cage 
of wood traversed by the central pivot. Care is taken to 
balance the two ends of the apparatus, by gradually adding 
weights to the arm not carrjiug the bird which is the subject 
of the experiment. 

If wo did not take this precaution, tho apparatus, as it 


1urns, would give lateral movements to tlie pivot on which it 
rests, and to the base itself. 

To furnish the bird with a solid point of suspension, pro- 
tected not only from vertical oscillations, but from move- 
ments of torsion, we have placed at each end of the instrument 
a cross piece of wood, to the two extremities of which are 
attached cords communicating with the ceiling of the room. 
At this point is a revolving hook, which turns freely with the 

Of the apparatus which suspends the bird Fig. 104 shows 
the details of this suspension which binds the biid to the arm 
of the instrument, while it confines as little as possible the 
libeity of its movements. 

Of the registering apparatus. The transmitting tubes are 
arranged along the arm of the instrument ; tln>y are fastened 
to it throughout all its length, and end in a register which 
carries three lever-drums tracing on the i evolving cylinder. 
The instrument in its rotation would cause the transmitting 
tubes to roll round its axis, if the register to which they are 
directed did not participate in the general rotation. 

We see in fig. 103 how this apparatus is arranged. The 
cylinder is placed vertically above the axis of the instrument; 
the three levers trace upon it. The whole apparatus rests 
on a tablet, which turns on the central pivot. We have here 
well-known arrangements, in which several movements are 
registered at the same time on the cylinder ; it will, there- 
fore, be useless to repeat the precautions which are to be 
taken in the management of the apparatus, such as the exact 
superposition of the tracing points, &c. 

The movements of the wing are extremely rapid; they can 
be registered only on a cylinder turning with great velocity ; 
that which is employed in this experiment makes one revolu- 
tion in a second and a half. The shortness of the time ,it 
our disposal to trace the movements of the bird compel us to 
do so only at the precise moment when the phenomena which 
we wish to observe are presented, whether it be the swiltebt 
flight, the gradual slackening of its speed, or the efforts 
made at starting. If the three levers were to rub constantly 
on the cylinder, we should soon have nothing but a confused 





scrawl. It is indispensably necessary so to arrange the 
instrument that the points of the levers should touch the 
cylinder only at the moment when we wish to register the 
phenomena, and to cease this contact after one, or at most 
two revolutions of the cylinder, in order to avoid confusion in 
the tracings. 

We have recourse, for this purpose, to the arrangements 
already made in our experiments upon walking. 

Fig. 103 shows the experimenter at the instant when he 
is about to take a tracing from the pigeon. Observing the 
flight of the bird, he seizes the moment when it becomes 
regular, aud squeezes the india-rubber ball. The contact of 
the levers is immediately produced, and the tracing is made. 
After a second and a half he censes to press it, the spring 
removes the levers from the cylinder, and the tracing is over. 

With a little practice it is very easy to ascertain the dura- 
tion of the revolution of the cylinder, and to confine the 
tracing to the necessary length. 

This long description was necessary, as we were anxious 
to make this apparatus understood, it being the most im- 
portant of all, on account of its double function. We shall 
have to employ it, not only in the analytical, but also in the 
synthetical part of these studies, when we shall attempt to 
represent the movements in the bird's Might. 

New determination of the trajectory <>/ a bird's winy. A 
pigeon was made use of in this experiment. It was a male 
bird of the variety called the Roman pigeon, very vigorous, 
and accustomed to fly.* Fig. 104 shows the arrangement of 
the apparatus which we have used for the purpose of study- 
ing its movements. 

It is more especially to the humerus that we have directed 
our attention, in order to obtain the movements of the wing in 
space. For this purpose a wire is twisted round the bone, 
holding it as in a ring, and furnishing by its free ends a firm 
point of attachment outside the wing for other wires which 
act on the experimental drums. 

This latter point is of great importance, for the greater part of the 
birds in a dove-cot are of no use to us, on account of their inexperience in 



The movements of the two wings being perfectly symmo- 
tiical in regular flight, we cause two wires, which pass sym- 
metrically from the wings, to converge to each of the experi- 
mental drums. Thus, drum No. 1, intended to give signals 
of the elevation and depression of the wing, receives two 
wires, each of which proceeds from one of the humerus hones 
of (lie pigern, at ahout 3 centimetres outside the articulation 
of the shoulder. These wires rise and converge, and are 
attached to the point of the lever No. 1 ; while from the 
same point proceeds an india-rubber thread,* which serves as 
a counter-spring, aud rises vertically to a hook above, which 
holds it. 

We have before seen (fig. 102) how the lever of the 
experimental drum receives, under these conditions, all the 
movements of elevation and depression executed by the 
humerus of the bird. 

Two other wires, each attached to the humerus of the 
pigeon on each wing, and starting from the same point of the 
bone to which were fastened the wires of drum No. 1, con- 
verge also, turning backwards, and proceed to the lever of 
drum No. 2. This is the drum which receives the movements 
exeeuled by the wing in the antero-posterior direction. The 
two drums send their signals by air tubes to the register 
situated in the centre of the apparatus. 

]''.r/'t'rh/u'iit. After having ascertained that the two levers 
intended to trace have their points situated on the same 
vertical, the pigeon is allowed to fly. The bird goes through 
the movements of flight, and soon carries round with con- 
sidemble rapidity the instrument to which it is attached. 
The operator, placed in the centre of the apparatus, has only 
to follow for u few paces the rotation of the instrument. 
J)ming this time he holds in his hand the india-rubber ball, 
and has only t<> compress it, in order that the two levers may 
n^t with their points against the blackened paper, and that 
the tracing may commence. As soon as the flight is well 
established, ai:d seems to be carried on under satisfactory 

* In fi. 104 a sjiir s]iriii has lioni sulisliluU-J for tliis india-rulilicr 


conditions, he compresses the ball, and produces the tracing 1 
represented in fig. 105. 

Fio. 105. Tracing of the movements of a pigeon's wing. Tbe upper lino, 
A P, shows the movements forwards and baekwarJs. Tlie lowir line 
H B, the movements up and down. 

Interpretation of the tracings. The curves are read from left 
to right, like ordinary writing. The upper curve is that 
described by the humerus of a bird in its movements for- 
wards and backwards ; the direction of these movements is 
indicated by the letters A and P, which signify that all the 
tops of the curves, as well as that at A, correspond Avith the 
time when the wing has reached the most forward part of its 
course ; the lower parts of the curves, on the contrary, indicate, 
as well as that at the point P, the moment when the wing 
has readied the hinder part of its movement. 

The horizontal line which cuts this curve has been traced 
in a previous experiment by the point of the lever at the 
instant when the wings of the bird, kept motionless by an 

-2,-. 1 


.oM-tant. may he considered ;ts hori/oiitally extended, tending 
neither forwards nor liackwards. This line represents, there- 
Inn', to some extent, the zern of the scale of the movements 
of tin- \\ing in its antero-posterior direction. The inspection 
ot the curve si io\vs us also, that the pigeon's wing was carried 
more especially in the direction of the upper parts, similar to 
the point A; in other terms, that the forward predominated 
over the Backward movement. 

!'!(. lut; SujMT]isiliiin of tliu preceding curves on p.iper dri'ie<l in inilli. 
iin tic--. The two curves hiive a common direction with reference t the 

Tlie same explanations would apply to the lower curve 
II P, which expresses the movements of the wing upwards 
and downwards 

In order to ascertain if the course of the pigeon's wing iu 
the present experiment is apparently the same as that of tlie 
lni//.ird recorded heiore, we have constructed the complete 
curve of the \\ing during one of its revolutions, making use 
for thi-~ 1'iirpoM' of the two partial curves of tig. 105. 

The following is the method employed in this ((instruction : 

In order to i;ive more facility to the measurement of the 
positions nf the different points of these curves, we have 
ccpied them l.oth on a paper graduated in centimetres ;. I 


millimetres. We have tniced in full line one of these curves, 
that of the movements in. the antero-posterior direction, the 
course of which is indicated by the letters A and P ; then \ve 
have represented, by a dotted line, the curve of the upward 
and downward motions with the letters H and 13. We have 
placed these two tracings over each other, so as to make the 
zero-lines of each coincide. We have also taken care to 
preserve the vertical superposition of the corresponding points 
of each of these curves ; we inny therefore be certain that, 
wherever any vertical line cuts the two curves, the inter- 
sections correspond with the position which the humerus of 
the bird occupies, at that instant, with reference to two planes 
at rig - ] it angles to each other. The intersection with the dotted 
line will express, by the length of the ordinate drawn from 
this point to the axis of the abscissa?, the position which the 
wing then occupies with reference to an horizontal plane ; the 
intersection with the full line will express the position of the 
wing as referred to a vertical plane. 

Tli is determination is realised in fig. 107 for the trajectory 
ol the wing, which has been constructed by successive points 
in the following manner: 

!sii:::::U:::i:HH;::ss sis:::;::;:::: I:::;::::: 

Fir. 107 Constructed from the preceding- curves. An arrow indicates the 
direction of the movement. The separation of the dots exprtsses the 
rapidity of the movements of the wing at the different parts of its 


Let there bo two lines, x x, forming the axis of tlio 
aKsrissiv, and y y that of the ordinates. Let us assume, that 
all which is above the Hue of zeros, iu the full curve that is 
to say, that which corresponds with a movement iu a forward 
direction, ought to point to the right of the line y y. In- 
versely, that all which is below the zeros, in the full curve, 
will point to the left of the axis of y y. The position with 
reference to this axis will be reckoned, parallel to it, by 
means of milliuietric divisions. 

On tlto other hand, the different measurements taken on 
the dotted curve (that which expresses the upward motion of 
the wing) must point to the corresponding elevation, reckoned 
above or below the line x x, according as these points in the 
curve of the elevations are removed a certain number of 
millimetres either above or below the ZL.TO line. 

Let us take as our point of departure, in the construction 
of the new curve, the point c (fig. 107), chosen on the dotted 
line, at one of the times when the wing has arrived at one of 
its anterior limits. 

This point, according to the millimetric scale, shows us 
that the wing is depressed 13 divisions beneath the horizontal 
line. Let us follow the vertical line which passes through 
the point c, till it meets with the curve of movement in the 
nntero-posterior direction : the intersection of this vertical 
lino with the curve shows us that the wing at this moment 
had been carried forward 26 divisions; on the new curve, 
therefore, the point a ought to bo marked at a well-ascertained 
position c, which will be found at the intersection of the thir- 
teenth division below the axis x JT, with the twenty-sixth to the 
right of the axis y y, which according to what we have as- 
Kiimcd, corresponds with 26 divisions iu the forward direction. 

To determine a second point in our curve, let us proceed, 
in reading the tracings, one millimetric division farther to 
the right; wo shall find, as before, the intersection of the 
vertical at this point with the two curves, and we shall thus 
h.ive a second point in the new construction determined. 

The scri' s of succps.-ive points obtained in this manner 
form a carve which shows the course of the wing; the arrow 
indicates the direction of the movement. 


By constructing thus the whole figure, we see that this 
curve, after pioceeding downwards and forwards, rises and 
returns back again. 

By comparing this figure \\iih that which we have obtained 
by means of another apparatus (fig 100), on another kind of 
bird, and by examining the n-ovement of another part of the 
wing, we shall find striking 'resemblances between the two 
curves, which show that birds proceed in their flight by 
movements which are almost identical. In fact, the bone of 
the wing in each describes a kind of irregular ellipse, with 
its greater axis inclined downward and forward. The im- 
portance of this determination is so great, that we trust we 
shall be pardoned for the long and minute details of the 
experiments which have furnished these results. 


We have seen in Chapter I. that the wing of the insect is 
subject to torsions under the influence of the resistance of the 
air, and that the inclination of the plane of its wing is 
changed at every moment. These movements, which are 
entirely passive, constitute the essence of the mechanism of the 
insect's flight; the wing, in each of its alternate movements, 
acts on the resistance of the air, and gains from it a force 
which is exerted on the membrane by the side of the main- 
rib, thus serving to sustain the insect and propel it forward. 
The structure of the bird's wing does not allow the existence 
of a similar mechanism. Its wing during its ascent does not 
present to the air a resisting plane, because the feathers which 
fold over each other would open to allow it to pass through. 
The depn snon of the wing is therefore the only phase in the 
flight of the bird which has any analogy with that of the 
insect. Besides, the curve described by the point of the bird's 
wing is sufficiently different from that of the insect, to prove 
that their mechanical conditions are very dissimilar. 

It was indispensable to determine by experiment the dif- 
ferent inclinations of the plane of the bird's wing at each 
phase of its revolutions. In fact, to estimate the resistance 
which the air presents at each moment of the flight, we must 
know the two elements of this resistance : first, the angle 


under \vliidi (he piano of the wing strikes the air, and 
secondly, the velocity with which it is lowered. Nothing is 
inure easy than to obtain the second data of the problem; 
we can reduce them from the curve which represents the 
position of the wing at each instant, a curve of which we 
hav.- an example in fig. 108, as obtained from a pigeon. But 
the difficulty which presents itself, is to obtain the indication 
of the changes which take place in the plane of the wing 
during flight. For this purpose we have had recourse to the 
following mechanism. 

We have seen, in fig. 99, that a rod connected with a 
Cardan universal joint, whose centre of rotation is near the 
Bcapulo-humeral articulation, can be made to represent ac- 
curately the circular movements of the wing. But Cardan's 
joint, though it obeys the rotary motions of every kind which 
are given to the rod, does not allow any movements of torsion 
with reference to the axis of this rod. 

Viu. 10S. Theoretical figure of tin- apparatus to investigate the torsion c.f 

the wing. 

Let fig. ION lie a kind of apparatus of this sort: we can 
give the rod / / every kind of motion in the vertical or hori- 
zontal direction; it will follow all the impulses which it 
receives. But if we take hold of the extremity of the rod, 
iM-ar the lever / which is perpendicular to it, and try to give 
the lever a movement of torsion, as if we were t lining a screw, 
the Cardan does not allow this movement t > be made, and tho 
rod re-i^ts the impulse brought to bear upon it. Let us 
ihat behind the Cardan joint, and on the prolonga- 
of the rod / /, there is another cylindrical rod, ;>, turning 
in a tube ; thi> rod will turn under the inllm nee of the torsion 
evicted by the hand holding the lever /, and if ihe rod j> 
curies a le\er /', at right angles to it,' and situuti d in the 


8 irae plane as I, we shall see that these levers correspond 
with each other, and that every change of plaue undergone by 
the first will be transmitted to the second. 

Under tl>ese conditions, if we cause the lever I to signal the 
changes of plaue which the wing undergoes in the various 
phases of its revolution, these changes will be communicated 
to the lever I', which can in its turn act on an experimental 
apparatus, and transmit the signal under the form, of a 
tracing. This is precisely the method which we have em- 
plovcd in our experiments. The lever / was placed upon the 
uing of the bird, and was held in a horizontal position. 
The lever I', also horizontal, was fastened by a wire to the 
lever of an experimental drum placed above it, and arranged 
in the same manner as in the experiments described in the 
former chapter. 

When we caused the plane of the wing to oscillate, so as 
to turn its upper surface more or less backwards, the registered 
curve was depressed; it rose, on the contrary, when we turned 
the wing so as to carry forwards. 

Siill a difficulty presented itself. It was not possible to fix 
the lever I at one point of the rod t t ; and, at the same time, 
to render it immovable at a single point in the bird's wing. 
In i'act, the Cardan joint, not having the same centre of motion 
as the articulation of the wing, it followed that in the vertical 
movements the rod slipped upon the wing. It was necessaiy, 
therefore, for the lever I, while fixed to the feathers of the 
bird, to glide freely on the rod in the direction of its length, 
and yet that it should causa it to receive, under the form of 
torsion, all the changes of inclination that are transmitted to 
it by the wings of the bird. We see in fig. 109 how this 
result has been obtained. 

Let 1 1 be the rod which is to follow all the circular move- 
ments executed by the bird. This rod has in it deep 
longitudinal grooves, which give its section the appearance of 
a star ; it glides freely in a tube which is applied to its 
external surface. But at one of the extremities of the tube is 
a metallic sliding casting, the interior part of which is grooved 
like a star, through which passes the rod whose grooves slide 
in those of the star-shaped opening. Then thu lever I is 


soldered to this tube, and is able to move with it to any point 
along tin- rod, thus allowing full liberty to tlic movements of 
(light, while no change of plane ran be effected without com- 
municating a movement of torsion to the red. 

After some experiments, it became necessary to mala; im- 
provements in this apparatus. Tin s, the lever I bad a tendency 
to get twisted on account of the displacement of the feathers 
during llight; it was replaced (Jig. 10'J) by u piece with three 

1 i>;. 10!'. Aotn.-il arniii^fniciit of tlic :i|i]vir;itus intciulcil to experiment, 
tlic movemeilta of tliu will,', ;iinlits ch.uigu tif 

niov.ilJe levers, lib, turning in the same plane round a 
common centre, like the blades of a fan. Each of these little 
braiu-hes terminated in a hook. After having attached the 
sliding tube to the false winy of the Lird, the extremity of 
ach of these three blades Avas tied to one of the long leathers 
of the uing. This ligature, made with india-rubber, gavo 
\ ellent results. 

The lever I (fig. 109) was also defective on account of its 
unequal action. In its stead was substituted a, pulley of short 
rudiiis, placid on the rod prolonged behind the Cardan joint. 
The thin cord / /, which was to transmit tho torsions of the rod, 
] a--i d round the wheel of this pulley. In this manner the 
rotation of the pulley, resulting from the torsion of the rod, 
always faithfully transmitted this torsion to the experimental 

To pnl an vnd to thi* long description of the instrument 

intend' d to Iran SIM it the signals of the elevation and depression 

of 1 lie \\ ing, let us mi ly ,xi v that I he ] /ii < e si t uatcd at 1 he base 

the I'M r / / i, inli nd( d to transmit the \ertical and 


horizontal movements by two systems of cords. For tlio 
vertical ones, a cord v goes to the lever of the experimental 
drum. The cord h transmits to another apparatus the 
movements in the horizontal, that is, iu the autero posterior 

Experiment. A buzzard to which this apparatus has Leeu 
adapted is harnessed to the instrument and allo\vrd to fly : \vo 
obtain at the same time the tline curves represented in 
fig % . 110. AVith these three data, we can construct, not only the 
trajectory of the wing, but the series of inclinations of its plane 
at the different points of its coirrse. 

The curve traced with a full line corresponds with the 
movements of the wing in an antero posterior direction. The 
point A, and those homologous with it, correspond with the 
extreme anterior position of the wing ; the point P witli the 
extreme posterior position. The curve formed of interrupted 
strokes indicates the relative height of the wing in space; the 
point H corresponds with the maximum elevation of the wing, 
and the point 13 with its greatest depression. 

These two first curves enable us to construct, by means of 
points, the closed curve* (fig. Ill) representing the trajectory 
of the buzzard's wing. It is by this trajectory that we shall 
determine the inclination of the plane of the wing at every 
part of its elliptical course. 

For this purpose, we must return (fig. 110) to the dotted 
curve S, which is the expression of the torsions of the wing at 
different instants. The positive and ordinates of this 
curve correspond with the trigonometrical tangents of the 
anglesf which the wing makes with the axis of the body.J 

* This curve is not always closed ; this is the case only when the flight 
ts extremely regular. 

t We must subtract algebraically from the angle found, a constant 
fjiiantity, the angle of 30 which the wing, during repose, makes with the 

J We cannot positively affirm that this axis is horizontal ; it seems 
rather that it is inclined so that the beak of the bird turns slightly 
upwards. This inclination of the axis would necessitate a correction in 
the absolute inclinations of the wing at the different points of its 


They enable us, therefore, to trace iii fig. Ilia series of 
liiu-s, each of which expresses, by its inclination with respect 

t<> tin- horizontal 
ifil t<> tlif l \\liidi tli.' plain v of th wing 
at this saint' portion of its course. 


The direction of tlie movement of the wing is read from above 
and forward, from H to Av. 

Fig-. Ill shows that the wing during its ascent assumes 
an inclined position which allows it to cut the air so as to 
meet with the minimum of resistance ; while in its descent, 
on the contrary, the position of its plane is reversed, so that 
its louer surface turns downwards and slightly backwards. 
It Jollows, that in its period of depression, the wing, by its 
obliquity, acts upon the resistance of the air, and while raising 
the body of the bird, carries it forward. We see, also, that 

Flo. 111. Inclinations of the plane of the wing with reference to the axis 
(Av) ot llie budy during flight. 

the inclination of (lie wing changes gradually, in the different 
phases of its elevation and of its descent. Especially in this 
hitter pha^e, the influence of the air in shaping the course of 
the wing is more evidently seen; it is, in fact, at the moment 
when the rapidity of its depression attains its maximum that 
we see the posterior edge of the wing turn up the more strongly. 

The wing, when it has reached the end of its descending 
course, changes its plane very suddenly. The explanation of 
this movement is very natural. As soon as the resistance of 
the air censes to raise the feathers, these, by their elastic-it}', 
return to their ordinary position, which they occupy during all 
the phase of elevation. 

Even the ellipse which forms the trajectory of the wing cm 


be explained by the resistance of the air. The muscular 

apparatus of the bird, like that of the insect, lias nothing to 
i!o with the course of the wing; elevation and depression arc 
almost all the movements that it can produce. But the 
resistance of the air during the phase of descent gives rise to 
i In- anterior convexity of the curve passed through, by means 
of ,i mechanism which we already understand. The posterior 
convexity which belongs to the ascensional phase is also 
explained by the action of the air on the lower surface of the 
wing, which it carries backward at the same time as it raises 
it. We must seek for the demonstration of this theory in the 
artificial representation of these- different movements. 



He-actions of the movements of the vig Vertical re-actions in di fieri nt 
species ; horizontal re-actions or changes in the rapidity of flight ; 
simultaneous study of the two orders of re-actions Theory of tho 
flight of the bird Passive and active ]urts of the \\ing Reproduc- 
tion of the DiechiUiL-in of the (light of the bird. 

IN order that we may follow, in studying the flight of the 
bird, the same plan which has guided our researches on the 
other kinds of locomotion, wo must determine what are the 
roaciimiiiry ell'rcts of each of the movements of the wing on 
the I -oily of the animal. 

1'wo distinct effects are produced during flight: by one, the 
hiid is sustained in opposition to its weight; by the other, it 
is subjected to a proj ulsive force which carries it from OHO 
ptace to another. Uut do we find that the bird, when sus- 
tained in the air, keeps nt a constant level, or docs it pass 
through oscillations in the vertical plane ? Dors it not 
lirnco, by the intermittent eilect of the flapping of its 
\virgs li-ing and falling nmiiuiis, of which the e\e c.m ! . tci t 



neither the frequency nor the extent ? Again, does riot the bird 
advance in its onward course with variable rapidity ? Shall 
we not find in the action of its wings a series of inipulses, 
which give to its advancing course a jerking motion ? 

These queries can be answered experimentally in the follow- 

ing manner. 

Since we have at our disposal the means of sending the 
r-ignals of movements to a distance, and recording them by 
tracings, Avhen these movements are made to pi'oduce a pres- 
sure on the membrane of a drum filled with air, we must 
endeavour to reduce to a" pressure of this kind the movements 
which we desire to study. 

The oscillations which can be effected by the bird in a hori- 
zontal plane must be made to exert on the membrane of the 
drum pressures alternately strong or feeble, in proportion as the 
bird mounts or descends. The same kind of experiment must 
be made on the variations in its horizontal rapidity. 

The question has been already solved for the vertical 
re-actions, by means of the apparatus represented iu fig. 28, 
when we were treating of terrestrial locomotion ; a slight 
modification will allow us to employ the same method to 
ascertain whether vertical oscillations are produced during 

FIG. 112. Apparatus intended to transmit to the registering instalment all 
tiic vertical oscillations of tbc bird. 

Fig. 112 shows the arrangement that we have adopted. 
The mass of lead is applied directly to the membrane; some 
Mire-work protects the upper surface of the apparatus from 
the friction of the feathers of I ho bird, which, without this 
precaution, might sometimes affect the form, of the tracing. 




C i 



c - 

C K 

C 2 





After having 1 convinced ourselves (hat the apparatus trans- 
mits faithfully the movements which are communicated to it, 
\ve connect it with the registering instrument by means of a 
long tube, and place it on the back of a bird, which is then 
allowed to fly. Experiments made on many different species, 
pigeons, wild ducks, buzzards, moor-buzzards, screech owls, 
have shown that there are very varied types of flight with 
respect to the intensity of the oscillations in the vertical 

Fig. 113 shows the tracings furnished by different species 
of birds. All these tracings, collected on a cylinder revolving 
with a constant rapidity, and referred to a chronographic 
tuning-fork vibrating 60 times in a second, enable us to 
ascertain the absolute and relative duration of the oscillations 
during the flight of different species of birds. 

We find from this figure, that the frequency and amplitude 
of the vertical oscillations vary much according to the species 
cf the bird. In order to ascertain the cause of each of these 
movements with greater accuracy, let us register at the same 
time the vertical oscillations of the bird, and the action of the 
muscles of the wing. If we make this double experiment on 
two birds which differ much in their manner of flight, such 
as the wild duck and the buzzard, we obtain the tracings 
represented in fig. 114. 

The duck (upper line) presents at each elevation of its 
wing two energetic oscillations; that at b, at the moment when 
the wing is lowered, is easy to be understood, as well as that 
at a, at the moment that the wing begins to rise again. To 
explain the ascent of the bird during the time of the elevation 
of the wing, it seems indispensable to refer to the effect of 
the child's kite, to which we have before alluded. The bird 
having acquired a certain velocity, presents its wings to the 
air as inclined planes; an effect is immediately produced, 
similar to the ascent of the hovering apparatus which trans- 
form their acquired velocity into ascensional force. The 
flight of the buzzard shows also, but in a less degree, the 
ascent which accompanies the upward movement of the 

Determination of variations in the rapidity of flijd The 



second question \\liich we have to solve relates to the deter- 
iniiiutiun of the various phases in the rapidity of flight. It 
niav receive, its isulutii)ii by the employment of the same. 
method. If the drum, loaded with a piece of lead, be placed 
ou the back of the bird so as to present its membrane, in a 
vertical plane that is, at right angles to the direction of flight, 

ii: 114. Iu the upper part we sec. ]>l:n'. <l :i)>. .vr mcli oilier, the muscular 

t'.-u-in^ (see )> j::2i. ami that of ihu vertiral i>si-ill;ilimis in a wil<l duck. 
I 'in Iff tin 1 iiiiilulatimi ", whirli slinw.s tin- cli 'V.i tii in uf thu win^'. is MM'II :i 
M'ftii-al i>M'illati 'ii ; ani.tlirf is M'L-M iin.lrr/i. thu tr:iriiiK ci >n < s|KHiilin^ 
witli tin' ili-pu -sii.ii ..I tin' win^'. In the lower hall' of tin figure arc 
t - ii in:' s rolli rtc'l fri.i 1 1 a In I //aril ; tin' o.-r illation at ". wliirli rorrr.s|ii nius 
with thu cluvatii'ii ot tin uin^, is IL-KS marked than that from the duck. 

the apparatus would be insensible to vertical oscillations, and 
\\onld only give the signal of those which are made backwards 
and forwards. Let us turn the membrane of the drum in 
iron) ; it. is evident that if the bird quickens its speed, the 
retarding- influence of the inertia of the mass of lead \\ill 
produce a pressure 071 the membrane of the drum ; (lie air 
will be compressed, and the registering lever will rise; while 


the slackening of the bird's speed will cause a descent of the 
lever by an inverse action. 

Experiments tried upon the species of birds before men- 
tioned, have furnished us with tracings analogous with those 
of the vertical oscillations. 

If it be true, as we have supposed, that the vertical 
oscillation of the bird, at the moment of the ascent of the 
wing, is due to the transformation of speed into elevation, 
we shall have the means of verifying this supposition, by 
collecting simultaneously the tracings of the vertical oscilla- 
tions and those of the variations of rapidity. 

Thus, by registering at the same time the two orders of 
oscillation in the flight of a buzzard, we find that the phase 
of depression of the wing produces at the same time the 
elevation of the bird and the acceleration of its horizontal 
swit'.ness. This effect is the natural consequence of the 
inclination of the plane of the wing at the moment of its 
descent ; this we already know from having obtained it in the 
flight of the insect. As to the elevation of the wing, it is 
found that during the slight ascent which accompanies it, the 
swiftness of the bird diminishes. In fact, the curve of the 
variations of rapidity is depressed at the moment when the 
bird rises. This is, therefore, a confirmation of the theory 
which we have propounded concerning the transformation of 
the horizontal rapidity of the bird into ascensional force. 
Thus by this mechanism, the stroke of the descending wing 
produces the force which will cause the two oscillations of the 
bird in the vertical plane. It produces directly the ascent 
which is synchronous with it, and indirectly prepares the 
second vertical oscillation of the bird by creating rapidity. 

Simultaneous tracing of the two orders of the oscillations of the 
bird. Instead of representing separately the two kinds of 
oscillation exectited by the bird as it flies, it is more instinc- 
tive to seek to obtain a single curve representing together the 
movements which the body of the bird makes as it advances 
in space. 

Tiie method which we have employed to obtain the move- 
ments of the point of the wing may, with certain modifica- 
tions, furnish the simultaneous tracing of the two orders of 


movement which we wish to investigate. For this purpose, the 
two drums combined rectangularly must be connected with the 
same inert mass. 

Let us refer to fig. 97 (p. 237), where we see the two 
lovers connected together and communicating with each other 
by tubes, which transmit to one all the movements executed 
by the other. When we give the first lever any kind of 
movement, we see it reproduced by the second lever in the 
same direction. 

Now, let each of these levers be loaded with a piece of lead, 
and taking in our hand the support of the apparnfrus, let us 
cause it to describe any kind of movement in a plane perpen- 
dicular to the direction of the lever. We shall see that tl.e 
lever No. 2 exi cutes movements of exactly an opposite kind. 
In fact, since the motive force which acts on the membrane of 
the drums is nothing more than the inertia of the mass of 
lead, and the movements of this mass are always later than 
those given to the apparatus, it is clear that if we raise 
the whole system, the mass will keep the lever down, while 
if we lower the instrument the mass will retain the lever 
above; that if we carry it forward, the inertia will keep the 
lever back, &c. Therefore, the lever No. 2, only going 
through the same movements as No. 1, will give curves which 
will be absolutely Opposed to the movement which has been 
given to the stand of the apparatus. This being assumed, lot 
us pass to the experiment; for this, let us employ the 
aop; ratus represented in fig. 99 on the back of the buzzard 
us it Hies ; let us remove the rod which received the movements 
of the wing, as well as the parallelogram which transmitted 
them to the lever ; we will only retain the lever fastened to 
the two drums, and the contrivance which fixes the who!o 
instrument on the back of the buzzard ; lastly, let us adapt a 
piece of lead to this lever, and let the bird fly. The tracing 
procured is represented in fig. 115. The analysis of this 
curve is at first sight extremely difficult; we hope, however, 
to succeed in showing its signification. 

Analysis of the curve illustrating the oscillations of the bird. 
This curve is described on the cylinder in the same manner as 
in fig. 100, which shows the different movements of the point 



of the wing ; the glass 
plate moves from right to 
left; the tracing must be 
read from left to right. 
The head of the l>ird is 
turned towards the left, 
its 'flight is in the direction 
pointed out by the arrow. 

We may divide this 
figure into a series of 
portions by means of ver- 
tical lines passing through 
homologous points, whe- 
ther we let fall these per- 
pendiculars from the top 
of the loops, or from that 
of the simple curves, as 
lias been done at the points 
a and e. Each of these 
portions will enclose toler- 
ably similar elements, with 
the exception of their un- 
equal development in the 
different points of the 
figure : let us neglect this 
detail for the present. 

It is evident that the 
periodical return of similar 
forms corresponds with the 
return of the same phases 
in a revolution of the bird's 
wing. The portion a e will, 
therefore, represent the dif- 
ferent movements of the 
bird in one and the same 

Let us remember that in 
the curve which we analyse, 
all the movements are con- 
Irary to those really per- 
formed by the bird. The 


two vertical oscillations of the bird, the greater and the 
less, must thus be represented by two curves, of which 
the summit will be placed downwards. It is easy to recognise 
their existence in the large curve, a b c, and the smaller one 
c d e. The bird was, therefore, rising from a to b, descending 
from b to c ; it rose again from c to d, and descended from 
d to e. 

But these two oscillations encroach on each oilier, which 
produces the loop c d ; the oscillation c d e partly covers the 
first by turning towards the head of the bird. Since the 
indications of the curve are in a direction contrary to the real 
motion, this is a proof that the bird, at this moment, was 
cither carried backwards, or at least slackened the rapidity of 
its flight. 

This figure, therefore, recalls all that the former experiments 
have taught us concerning the movements of the bird in 
space. We see from them, that at each revolution of its wing 
it rises twice, followed by two descents; that these oscillations 
are unequal : the larger one, as we know, corresponds with the 
lowering of the wing, the smaller one with its elevation. Wo 
see, also, that the ascent of the bird, while tho wing is rising, 
is accompanied by the slackening of its speed, which justifies 
the theory that this re-ascent is made at the expense of the 
velocity acquired by the bird. 

But this is not all : fig. 115 shows us, also, that the move- 
ments of the bird are not the same at the commencement as 
at the end of its flight. We have already seen (figs. 95 and 
100) that ihe strokes of the wing at its departure are more 
extended; we see here that the oscillations produced at its 
departure by the descent of tho wing (shown at the left hand 
of l he figure) are also more extended. But theory enables us 
to foresee that the oscillation of the ascent of the wing, being 
produced by the velocity of the bird, must be very feeble at 
the commencement of its flight, when the bird has, as yet, but 
little rapidity. This figure shows us that this is actually tho 
case, and that at the beginning of the flight, tho second 
oscillation of the wing (that which forms the loop) is but 

Wo are now, therefore, in possession of tho principal 



notions on which may be established the mechanical theory of 

From all these experiments we may deduce that it is 
during the descent of the wing that the bird acquires all the 
motive force which sustains and directs it in space. 

Theory of the flight of the bird. On this subject, as on 
almost all those that belong to this discussion, nearly every- 
thing has been already said ; so that we must not expect to 
find an entirely new theory arise from the experiments which 
have been described. In the works of Borelli we find the 
first correct idea of the mechanism of flight. The wing, 
says this writer, acts on the air like a wedge. Developing 
still farther the thought of the learned Neapolitan physiologist, 
we should now say that the wing of the bird acts on the air 
after the manner of an inclined plane, in order to produce a 
re-action against this resistance which impels the body of the 
bird upward and forward. This theory, confirmed by Strauss- 
Durkheim, has been completed by Liais, who noticed the 
double action of the -wing ; first, that which in the phase of 
depression of this organ, raises the bird and gives it an im 
pulse in a forward direction ; then, the action of the ascending 
wing, which is guided in the same manner as a boy's kite, 
and sustains the body of the bird until the following stroke 
of the wing. 

We have been reproached for relying en a theory which 
had its origin more than two centuries ago ; we much prefer 
an old truth to the most modern error ; therefore we must be 
allowed to render to the genius of Borelli the justice which 
is due to him, and only claim for ourselves the merit of having 
furnished the experimental demonstration of a truth already 

But the theories which had been propounded up to the 
present time neglected many important parts which experi- 
ments reveal, and which we are about to endeavour to bring 
clearly forward. 

Thus, the manner in which the change in the plane of the 
wing is effected in every part of the night was necessary to 
be known, in order to explain the re-actions which tend 


always to sustain the body of the bird, sometimes by acceler- 
ating the rapidity of its flight, sometimes by slackening it.* 
Fig. Ill shows this change of plane. 

As to the re-actions to which the body of the bird is sub- 
jected, experiment has clearly demonstrated them ; it has 
furnished us with the means of estimating their absolute force. 
\\V have seen that these re-actions differ according to the 
species of bird which is observed. They are powerful and 
sudden in birds which have a small surface of wing; longer 
and more gentle in birds formed for hovering; the re-action 
of the period of the re-ascent of the wing disappears almost 
entirely in the latter kind. 

If we could compare terrestrial locomotion with the flight 
of birds, and assimilate alternate with simultaneous move- 
ments, we might find certain analogies between the walk 
of man and the flight of the bird. In both, the body is 
urged forward by an intermittent impulse ; man, like the 
bird, raises himself by borrowing the necessary work from 
the ilifiiuiiiic energy which he has acquired by his muscular 

As to the estimation of the work expended in flight, we 
must, before we can undertake it, have a perfect knowledge 
of the resistance which the air presents to surfaces of every 
form, inclined at different angles, and possessing varied velo- 
cities. We only know as yet the movements of the wings ; 

* "We onglit to beg the reader to remark that the inclinations repre- 
sented iii fig. Ill are referred to a line which probably is not horizontal 
during flight. In fact, this line does not correspond with the axis of the 
body of the bird, for it was suspended in the apparatus by a corset placed 
behind its wings, and thus had its centre of gravity in trout of the point 
of suspension, which caused its beak to hang .slightly down. In five 
11 glit, mi the contrary, the axis of the bird is horizontal or rather turned 
somewhat upward. l.YMoi-ed to this proper position, a fresh direction 
would be given to each of the positions of the wing (tig. Ill), which 
would alter them all by the same number of degrees. Then, probably, 
we should sec that the wing always presents its lower Miil'acc to the air, 
as the only one which can find in it a point of resistance. This supposi- 
tion rci|iiiivs for its verification some fresh experiments, which we hope to 
be soon aUe to make. 


the resistance which they meet with in the air has yet to be 
determined. Our experiments on this subject are still being 
pursued. When once we have these two elements, the mea- 
sure of work will be obtained from the resistance which is 
presented to the wing by the air at every instant, multiplied 
by the distance passed over. This will give us the measure 
of work bi'ought to bear upon the air. 

For its horizontal advance the bird will be obliged only to 
furnish the quantity of work equivalent to the resistance 
presented by the air in front of it, multiplied by the distance 
passed through. A part of this resistance, namely, that 
which is applied to the lower surface of the wing, is utilised 
to sustain the bird, by the kind of action which we have com- 
pared to that of a child's kite. 

It appears that this action is of primary importance in the 
flight of the bird. In fact, among the researches on the 
resistance of the air there is one which we owe to Mons. de 
Louvrie, which seems to prove that if the wing make a very 
small angle with the horizon, nearly all the work obtained 
from the dynamic energy of the bird is employed to sustain 
it ; according to this writer, an angle of 6 30' would be the 
most favourable to the utilisation of its energy. The im- 
portant part played by the gliding of the wing upon the air 
seems also proved by the shape of that organ. The wing 
being alternately active when it strikes the air, and passive 
when it glides through it, is not, in all its parts, equally 
adapted to this double function. 

When a surface strikes the air, it must move with rapidity 
in order to find resistance. Thus the wing, turning around 
the point by which it is attached to the body, shows unequal 
and gradually-increasing velocity in different points according 
as they are nearer to the body, so that being almost nothing 
at the point of attachment of the wing, the velocity will be 
very great at the free end. 

Let us imagine the wing of an insect as large at the base 
as at the extremity ; this size would be useless in the part 
nearest to the body, for the wing, at this point, has not suffi- 
cient rapidity to strike the air with effect. Thus we find, in 
the greater part of insects, the wing reduced to a strong 



ncrvure towards its base. The mcmLranous part commences 
only at the point where rapidity of movement begins to be 
of some use, and the membrane goes on increasing in breadth 
till near the extremity of the wing. Such is (fig. 116) tin- 
type of the wing essentially active that is, intended only to 
strike (lie air. 

FUJ. lid. Wing of an insect. 

In the bird, on the contrary, one of the phases of the 
movement of the wing is, to a certain extent, passive ; that, 
is to say, it receives the pressure of the air on its lower sur- 
face, when the bird is projected rapidly forward by its 
acquired velocity. Under these conditions, the whole bird 
being carried forward into space, all the parts of the wing 
are moved with the same rapidity ; the regions near to tin; 
body are as useful as the others to take advantage of the 
action of the air which presses on them as on a kite. 

I 10. 117. Act. vu iiinl i>:issivc i>:irts of the bird's \viiig. 

Thus, the base of the wing in the bird, far from being re- 
duced, as in the insect, to a rigid but bare rib, is very wide, 
and furnished with fmt/n r.s- and irin;i rarri-ts which constitute 
a lar-e surface, under which the air presses with force, and 
in a manner very rllicat ious to sustain the bird. Fig. 117 
gives an idea of the arrangement of the wing of the bird, at 
the same time active and passive. 

The inner part, deprived of snllicient velocity, may be 


considered, while it is being lowered, as the passive part of the 
organ, while the external part, that which strikes the air, is 
the active portion. 

By its very great velocity, the point of the wing must meet 
with more resistance from the air than any other part of this 
organ ; whence the extreme rigidity of the large feathers of 
which it is formed. 

The conditions of decreasing rapidity explain the flexibility 
which becomes greater and greater in the feathers of those 
parts of the wing nearer to the body, and at last the great 
thinness of those at the base or passive part of the wing. 

Let us add that the effect of the kite must be produced at 
the base of the wing, even while the point strikes the air, so 
that the bird, as soon as it has acquired its velocity, would 
be constantly lightened of part of its weight, on account of 
this inclined plane. 

The reproduction of the mechanism of '/light now occupies the 
minds of many experimenters, and we hesitate not to own 
that we have been sustained in this laborious analysis of the 
different acts in the flight of the bird, by the assured hope of 
being able to imitate, more or less imperfectly, this admirable 
type of aerial locomotion. We have already met with some 
success in our attempts, which have been interrupted during 
the last two years. 

Winged apparatus has been seen in our laboratory, which 
when adapted to the frame-work which had held the bird, 
gave it a rather rapid rotation. But this was only a very 
imperfect imitation, which we hope shortly to improve. 
Already a young and ingenious experimentalist, Mons. 
Alphonse Penaud, has obtained much more satisfactory results 
in this direction. The problem of aerial locomotion, formerly 
considered a Utopian scheme, is now approached in a truly 
scientific manner. 

The plan of the experiments to be made is all traced out : 
they will consist in continually comparing the artificial instru- 
ments of flight with the real bird, by submitting them both 
to the modes of analysis which we have described at such 
length ; the apparatus will, from time to time, be modified 
till it is made to imitate these movements faithfully. For 


this purpose we are about to undertake a new series of ex- 
periments ; some new apparatus is being constructed, which 
will soon be finished. 

We hope that we have proved to the reader that nothing 
is impossible in the analysis of the movements connected with 
the flight of the bird : he will no doubt be willing to allow 
that ine.-haiii^m can always reproduce a movement, the nature 
of which has been clearly defined. 


Action and reaction, 109 

Air, resistance of, changes plane of 

insect's wing, 197 
Aliment, heating power of, 16 
Animal motion, 27 
Animals, high temperature of, 21 

warm and cold blooded, 23 
Apophyses, cause of, 89 
Automatic regulator of temperature, 



Beclard's experiments on heat and 

work, 17 
Bernard on automatic regulator of 

temperature, 25 

Bertrand on birds' muscles, 212 
Biped diagonal, definition of, 154 
B rds, conformation of, 216 

.curves in wing of, 210 

electrical experiment on 

flight of, 231 

flight of, 209 

hovering of, 221 

large pectoral muscles of, 211 

M. de Lucy on, 222 

muscular force of, 213 

passades of, 220 

rapidity of muscular action 

in, 214 

ressource of, 220 

sailing flight of, 221 

stable equilibrium of, 216 
Birds' wings, compared to screw, 211 

duration of elevation 

and depression of, 229 

stroke of, forward and 

backward, 235 
Blood, circulation of, 67 

Bones, change in through age, 90 

Borelli on locomotion, 103 

birds' muscles, 212 
flight of birds, 273 
horse, 161 

Buzzard, muscular force of wing of, 


Chronograph described, 122 
Circulation of blood, variations in, 

furrows the 
bones, 87, 88 
Climbing, 106 
Club-foot, 96 
Creeping, 105 
Cnruieu on Eclipse's gallop, 167 


Darwin's natural selection, 79 
Darwinists, suggestions to, 84 
Davy on torpedo, 52 
Development theory, 78 
Diptera, manner of flight of, 208 
Dromedary, paces of, 173 
Duges on movements of horse, 139 
Duhamei's chronogr;iphic tuning- 
fork, 44 

Duval, representation of horse by 
zoo trope, 177 


Electric fishes, 51 



Lie. trieiiy, ;miin:il, 49 

disappearance when te- 
tani/'-d, ."'" 

Du Bois lii-ymoud on, 


TIM -ehanical \viirk substi- 

tute,! for. .M 
D'Esterno on flight of birds, 221 


Fibre, striped ami un. striped, 28 

and tendon, 69 

in old age replaced by t> inl'n, 

Force, what, 5 

all can be reduced to motion, 8 

indestructible, t!, 13 
potential, 12, 14 

Flight, see Win;,'. 

of bux/anl, 2G1 

of birds, 2u'.i 

of pigeon, -jri'i "f, imitated, 277 

sailing, "f birds, 'J21 

Blight waste of substance in, 


Frog, signals, 32 

"Function makes the organ," Guerin, 


Gorilla, skull in old and young, 90 
lim-riii on club foot, 97 

on change of bones through 

age, '.'u 

theory of function, 84 

Hartin"s on ratio "f bird-,' \viiiL r >t 

weight, -!*;, -J24 

II. at, animal, 19 

loxs of, in external organs, -_"J 
un I'hanii'al equivalent <>l, l ." 
unit of, 13 

Helmholtz on contraction of muscles, 

/ on lost time in mn.srnlar 

adion, 48 
lIiTilciihi-im's cxiicriiin nts mi h.-at 

and work, 17 
Him on and work, 18 

I biiiiolngy nf llillsc'lr-, 7'! 

Jlorsr not jn-ojcrtrd into air, 156 

paces of, I-"; 1 


transition of paces of, 172 

various authors on, II.". 

Vilirrnt 'and I Miill'oli nil, 151 

xoiitro]ir ligun-s of, 177 
Hovering of birds, -j-Jl 
llumerus, curvatures in brad of. i;> 

a contorted fnuur, '.'1 


India-rubber, change of heat into 
work in, 39 

Joule on equivalence of force, 15 


Kalridophone rod, Inn-ing of, 191 
with wing ot 

wasp, ]::', 

Kangaroo, development of crural 
s in, 71 

Lamarck's development theory, 77 
Latoiir on movement of bird s \\inu, 

Lavoisier's theory of animal heat. 2'' 
Levers in animal skeletnn, i'.."i 
Liais on double action of bird's 

\\ing, 27=5 
Lite, organic acts nf, 28 

MI relal Ion, -^ 

Lneiiiiiotiiin. aerial, ISO 277 

aijiiatii-, lnii 
terrestiial, K'2 



Lest time in muscle, Ilelmholtz, 43 
Lucy, M. de, oil wings of birds, 222 
Lungs, not seat of combustion, 23 


Marey's myograph, 32 

Matteucci on torpedo, 52 
Mechanical work, estimation of, Gl 

forms of, 60 
Mechanism of flight, reproduced, 

Modification of animals, 100 

of men, 101 
Momentum, divided between gun 

and carriage, 110 
Moreau on torpedo, 53 
Motion, all force reduced to, 8 
alternate in living motive 

powers, 66 

Motors, living, dynamic energy of, 68 
Movements, see Tracings 

caused by muscles in 

insect's wing, 106 
of snail, 105 
of wing of birds, 226 

insects, 195, 


Muschelbroeck on torpedo, 52 
Muscles, absorption of, from disease, 

adaptation of, to function, 


change of, by age, 99 

by experiment, 

fatty degeneration of, 97 

harmony between form and 

function in, 77 

homology of, 73 

in jaw of carnivorn, 90 
in man and ape, 75 

large, slight contraction of, 

lateral dilatation of, 36 

long and short, 70 

mechanical force in, 39 
pectoral in birds, 72, 211 

penniform, 70 

use of, acquired by habit, 


Muscles, work of, 47 
Muscular current, negative varia- 
tion of, 50 
contraction, tone heard 

in, 46 

force of birds, 213 
of tissue, 64 
shocks, 50, 51 
system, variation in, 94 
tissue, specific force of, 

wave, 35 

speed of, 38 
Myograph, explanation of, 31 


Nerve, function of, 41 
Nervous agent, speed of, 42 

Du Buis Reymond 
on, 41 

centres command action 

without the influence of 
the brain, 29 
tetanus, 45 
Notation of p.ices, man, 134 

horse, amble, 142 

- gallop, 165, 


trot, 144 

lar, 156 

walk, 142, 


synoptical table 

of, 145 

rule, 175 


Oscillation of body, 113 
Oxidation of blood, 20 


Passades of birds, 220 
i Peiia ud's flight instrument, 277 



1'ettigrew, Dr., on birds' wings, 210 
Piste, definition of, 152 

of amble, lo'2 

of slow gallop, 167 

of Eclipse's gallop, 167 

of trot, 157 

of walking pace, 162 

I'line on stable equilibrium of birds, 


Reactions defined, 115 

instruments to show, 116 
of movements of wing of 
birds, 264 

of walking (man), 127 

of leap, ditto, 131 
of gallop, ditto, 131 
of trot of horse, 153 

of gallop, ditto, 165, 171 
Regnault's equivalent of heat, 15 
I.Vssource of birds, 220 
]( ymond, du liois, on muscular 

shocks, 50 

IMiythm of paces, 133 
Running (man), 125 


Selection, natural, 81 
Shuc, experimental, 113 

Skeleton, action o[ aneurism on, 87 
variability of, 85 

change of course and at- 

tachment of 
muscles, 89 

in, transmitted 

to descendants, 

hollows worn by tendons 

in, 86 

Snail, movements of, 105 
Step mrves, 127 

of horse's trot, 1.":; 
gallop, I 1 '."' 

walk, I'lo 

Stiniiilns <>f necessity. S! 
S\ nUn tic ri'prodnetinii of move- 
ments in man, 137 
in horse, 177 


Temperature of animals, 23 
Tetanus, muscular, 45 

from strychnine, 46 

heat developed in. 49 
Yolta and Weber on ner- 
vous, 45 

Thermodynamics, 14 
Torpedo, experiments on, 52 

lost time in, 56 
Tracings, sec Table of Illustrations, 
of walking pace (man), 


of running (man), 128 
of gallop (man), 131 
of hopping (man), 132 
of leaping (man), 131 

of movements of insect's 

wing, 190 ct .-"/. 

of action of pectoral mus- 

cles of birds. 1M2 

of (light of wild duck, buz- 

zard, &c., 266 

of Whcatstone's rod with 

wing of wasp attached, 


of humming-bird moth, 

compared with vibrations 

of chronograph, 121 
Traction, ell'ects of, ou skeleton, 

Trajectory of pubis, 119 

of bird's wing, 234-240 
Transitions in paces of horse, 174 


Unit of heat, 13 
of work, 14 


Veratrino, muscle under, 35 , 

Villenenve, Dr., on birds' wings, 223 
Vincent and GoilFon on horse, 151 
Volta and Weber on nervous te- 
tanus, 45 



Walking (man), 111 

(horse), 142 
Wing (bird's) 

action downward and back- 

ward at each stroke, 235 

active and passive parts of, 


ascent of, like action of boy's 

kite, 273 

analogy to human arm, 211 

at each revolution of, bird 

rises twice, 272 

change of plane in, 244, 


compared to screw, 211 

curves in, 210 

depression of, elevates and 

carries forward the body, 

descent of, gives all motive 

force, 273 

duration of elevation and 

depression of, 228 

frequency of strokes of, 227 
. Hartiugs on, 223 

instrument to show change 

in plane of, 258 

inclination of, changes gra- 

dually, 263 

M. de Lucy on, 222 

Louvrie', M. de, on angle of 

plane of bird's wing, 275 

movements of, 226 

ratio to weight, 222, 225 

Wing (birds') continued. 

re-action of movements of, 

on body, 264 
of wild duck, 
&c., 267 

trajectory of pigeon's, 255 
Wing (insects') 

act as inclined planes, 200 

artificial representation of, 


causes of movement of, 196 

changes in plane of, 190-204 

figure -of-8 movement of, 195 

flexible membrane of, 208 

flight instrument, illustrat- 

ing, 206 

frequency of movement of, 


moves downward and for- 

ward, 197 

movements of, determined 

optically, 187 

propulsion of, from below 

upward and forward, 204 

shape of, 276 
structure of, 196 

trajectory of (Or. Pettigrew), 

Work, mechanical, 60 

unit of, 16 


Zootrope, 137 

Zuckung, shock of muscles, 30 




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