Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/textbookofphysio02gamg r>^. Cr^^^''^^ A TEXT-BOOK OF THE PHYSIOLOGICAL CHEMISTRY OF THE ANIMAL BODY. ^ A TEXT-BOOK " 'm OF THE PHYSIOLOGICAL CHEMISTRY OF THE ANIMAL BODY INCLUDING AN ACCOUNT OF THE CHEMICAL CHANGES OCCURRING IN DISEASE BY ARTHUH GAMGEE, M.D., F.R.S., EMERITUS PROFESSOR OF PHYSIOLOGY IN THE OWENS COLLEGE, VICTORIA UNIVERSITY, MANCHESTER ; LATELY FULLERIAN PROFESSOR OP PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, ETC. WITH TWO CHROMO-LITHOGR'APHIC CHARTS BV SPILLON AND WILEWSON. VOL. IL THE PHYSIOLOGICAL CHEMISTRY OF DIGESTION. MACMILLAN AND CO. AND NEW YOBK. 1893 YAH Rights reserved.] 'rTf7s .308 Glycocine 308 Taurine 311 Sect. 8. The Bile Colouring Matters . 313 Historical Introduction 313 Bilirubin 31.5 Bihverdin 322 Sect. 9. Some Derivatites of the Normal Biliary Colouring Matters . 325 Hydrobilirubin 32-5 Biliary Urobilin (?) 327 BiUcyanin 328 Choletelin 329 Sect. 10. Imperfectly investigated Colouring Matters not pbe-existext IN Bile, but derived from Chromogens existing in it . . 332 Cholohaematin .332 Sect, 11. The Mucoid Nucleo-Albumin of the Bile 335 Sect. 12. The Cholesterin, Fats, Soaps, Lecithin and remaining Organic Constituents of the Normal Bile 339 CONTENTS. XV PAGE Sect. 13. The Minekal Constituents of Normal Bile 341 Sect, 14. The Gases of the Bile 343 Sect. 15. Summary of the Quantitative Composition of the Bile in Man AND CERTAIN OF THE LoWER AnIMALS ...... 344 Human Bile 344 Bile of the Dog 346 Bile of certain other animals 347 CHAPTER V. THE BILE (continued). Sect. 1. Eecapitulation of the Facts relating to the Origin of the Specific Constituents of the Bile 348 .Sect. 2. Discussion of the Question ■whether the Bile is to be considered A DiGESTrvE Secretion. The Action of the Bile on Carbo- hydrates, Proteids and Fats 351 The Antiseptic and Laxative Actions of the Bile . . . .356 CHAPTER VI. THE MODE OF PEODUCTION AND THE PHENOMENA OF ICTERUS OE JAUNDICE. ICTEEOGENIC POISONOUS AGENTS. THE MODIFICA- TIONS IN CHEMICAL COMPOSITION WHICH THE BILE EXHIBITS IN DISEASE. THE INFLUENCE OF DEUGS ON THE SECEETION OF BILE— CHOLAGOGUES. THE ELIMINATION OF MEDICINAL AND POISONOUS AGENTS BY THE BILE. Sect. 1. The Mode of Production and the Phenomena of Icterus or Jaundice. Icterogenic Poisonous Agents .... 359 Does a Hfematogenic, as distinguished from a Hepatogenic, Jaundice exist ? Icterogenic Poisonous Agents 362 Does a ' Urobilin Jaundice ' exist ?....... 366 Sect. 2. The Modifications in Chemical Composition which the Bile exhibits in Disease ......... 366 The secretion of the Gall-Bladder in so-called Hydrops Cystidis FeUeffi 369 Sect. 3. The Influence of Drugs on the Secretion of Bile. Cholagogues 370 Sect. 4. The Elimination of Medicinal and Poisonous Agents in the Bile 374 Passage of Pathogenic Micro-Organisms into the Bile . . . 376 XVI CONTENTS. CHAPTER VII. THE FORM, STRUCTURE AND CHEMICAL COMPOSITION OF BILIARY CALCULI. CHOLELITHIASIS AND THE THEORIES ADVANCED TO EXPLAIN IT. PAGE Sect. 1. The Frequency of Occurrence, the Form, the Classification AND Structure of Gall-stones 377 Sect. 2. Enumeration of the Constituents as yet found in Gall-stones. The Pigments which are only found in Gall-stones (Bili- FUsciN and Bilihumin) 381 Sect. 3. The Mode of Formation of Gall-stones 383 Sect. 4. Results of Quantitative Analyses of the Chief Varieties of Biliary Calculi 389 CHAPTER VIII. METHODS FOR THE ANALYSIS OF THE BILE AND BILIARY CALCULI. Sect. 1. Examination of the Bile for Albumin, Oxyh-emoglobin and its Derivatives, Sugar, Urea, Leucine and Tyrosine . . . 391 Sect. 2. Quantitative Determination of the Specific Gravity, Total Solids, Salts, Mucoid Nucleo-.u.bumin, Bile Acids, Fats, Soaps, Cholesterin, Lecithin and Bile-colouring Matters . 392 Sect. 3. The Methods of Analysing Gall-stones 396 CHAPTER IX. THE INTESTINAL CANAL AND ITS SECRETION. THE INTESTINAL JUICE OR SUCCUS ENTERICUS. Sect. 1. Introductory Observations on the Structure of the Intestinal Tube ... - 397 The Small Intestine 397 Sect. 2. The Retiform or Reticular (Adenoid) Connective Tissuk of the Intestinal Mucous Membrane 401 EeticuUn 403 Sect. 3. The Intestinal Juice or Succus Entericus 405 The Methods of obtaining Intestinal Juice 405 The Secretion of Intestinal Juice and the Conditions which in- fluence it ........•• . 408 Sect. 4. The Physical and Chemical Characters of the Intestinal Juice 412 The Enzymes of the Intestinal Juice 412 CONTENTS. XVU CHAPTER X. THE CHEMICAL PEOCESSES WHICH HAVE TBEIB SEAT IN THE IN- TESTINES AND WHICH ABE THE RESULTS OF THE ACTIVITIES OF MICBO-ORGANISMS. THE PRODUCTS OF THESE PROCESSES. PAGK Introductory Bemarks 418 Sect. 1. Thh Decomposition of the Pboteids under the Influence of Bactebial Action 419 1. Indol 421 2. Skatol 424 3. a-Skatolcarbonic Acid . 426 Derivatives of Tyrosine found in the Products of the Bacterial De- composition of Proteids ........ 428 Hydroparacumaric Acid 429 Para-oxyphenyl-acetic Acid 430 Phenyl-acetic and Phenyl-propionic Acids 430 Phenaceturic acid 432 Phenols resulting from the Putrefactive Decomposition of Tyrosine. Parakresol. Phenol 432 Non-occurrence of Ptomaines as Products of Normal Intestinal De- composition 435 Sect. 2. The Decomposition of the Carbo-hydrates in the Small Intestine UNDER THE INFLUENCE OF BaCTERIAL AcTION .... 436 Sect. 3. The Decomposition of the Fats in the Small Intestine under THE Influence of Bacterial Action 438 Sect. 4. The Gases op the Small Intestine 438 CHAPTER XL A BRIEF SUBVEY OF THE PROCESSES OCCURRING IN THE SMALL INTESTINE IN EELATION ONE TO THE OTHER. THE DESTRUCTION OF THE DIGESTIVE ENZYMES. Newly-discovered Facts tending to prove that none of the water ingested is absorbed by the stomach, but passes into the intestine 439 Recapitulation of the Chemical Processes occurring in the Small Intestine 443 XVIU CONTENTS. CHAPTER XII. THE L.MIGE INTESTINE AND THE PROCESSES WHICH HAVE THEIB SEAT IN IT. THE F.ECES IN HEALTH AND DISEASE, THE IN- TESTINAL GASES. INTESTINAL CONCRETIONS. PAGE Sect. 1. Preliminauy Observations on the Arrangement and Structure of THE Large Intestine 448 Sect. 2. The Characters of the Intestinal Contents as they pass from THE Ileum into the Large Intestine 449 Sect. 3. The final Digestive Processes in the Large Intestine. Its Powers of Absorption 451 Sect. 4. The Micro-Organisms of the Colon anu their Products. The Conversion of the contents of the Colon into F.bces . . 453 Sect. 5. The F.eces in Health 456 The Meconium 461 Sect. 6. The F^ces in Disease 462 Sect. 7. The Gases of the Large Imtestine 466 Sect. 8. Intestinal Concretions 467 CHAPTER XIII. CONCERNING THE MODIFICATIONS OBSERVED IN THE CHEMICAL PROCESSES OF DIGESTION IN SOME DIVISIONS OF THE ANIMAL KINGDOM. Sect. 1. Intr.\-Cellular Digestion in the Lower Invertebrata . . . 468 Sect. 2. The Function of the so-called ' Liver ' of Mollusca . . . 472 Sect. 3. Some Peculiarities or the Digestive Process in Fishes . . . 473 Sect. 4. Some Peculiarities of the Digestion of Birds .... 473 Sect. 5. Digestion in the Herbivora 475 APPENDIX. I. Neumeister's Views concerning the Albumoses, and their relations to the Albu- minous Molecules on the one hand, and to Peptones on the other . . 485 (Supplementary to pages 131 and 132.) II. On the separation of Proto- from Deutero-Albumose 488 (Supplementary to pages 125 and 129.) CONTENTS. XIX in, PAGE On the Diffusibility of Albumoses and Peptones 489 (Supplementary to pages 135 and 141.) IV. Kithne's New Method of separating Albumoses from Peptones, and for the Preparation of the latter 490 (Supplementary to pages 136 and 137.) Notes and Additions on the Nature of the Acids of the Gastric Juice and Gastric Cqptents 495 (Supplementary to pages 92 — 95 and 179.) 1. On the Colour Eeactions which may be employed in the investigation of the Acids of the Gastric Juice and Gastric Contents 495 2. On the systematic use of certain Colour Eeactions in determining the presence of Mineral and Organic Acids in the Contents of the Stomach, and on the Quantitative Estimation of the 'Total Acidity,' and of the ' Acidity ' due to Free Acids (Martius and Liittke) 497 1. Determination of Keaction. Is Hydrochloric Acid present ? . . 497 2. Quantitative Determination of Total Acidity 498 3. Quantitative Determination of Free Acids 498 3. Additional Methods of determining the Acids and especially the Amount of HCl in the Gastric Juice 499 (Supplementary to pages 95 — 100 and 178—182.) 1. The Method of Cahn and v. Mering for the determination of the total Hydrochloric Acid, the Volatile Acids, and the Lactic Acid of the Contents of the Stomach ... .... 499 2. The Method of Sjoqvist modified by v. Jaksch of determining the total HCl in the Gastric Contents ....... 500 3. The Method of Hayem and Winter for determining the free arid combined HCl of the Gastric Contents 501 4. Liittke's Method of determining the total quantity of Hydrochloric Acid in the Gastric Contents ........ 502 (A) The Principles on which the Method is based . . . 502 (B) The Standard Solutions employed in Liittke's process . 503 (C) The Actual Process of Analysis 504 VI. On Methyl-Mercaptan as a product of the putrefaction of Albuminous Sub- stances and as a Gaseotis Constituent of the Large Intestine . . . 506 (Supplementary to pages 420, 428, 466.) Index 507 CORRIGENDA. Page 129, six lines from bottom, for 'hetero-' read 'deutero-'. 129, five lines from bottom, for 'hetero-' read 'deutero-'. 131, six lines from bottom, for ' hemi-deutero-albumose ' read ' anti-deutero- albumose.' 181, first line from bottom, for ' 1859 ' read ' 1852.' 216, seven lines from top, for ' vi.' read 'ix.' 247, twenty-nine lines from top, for ' Para-oxyphenyl-a-propionic acid ' read ' Para-oxyphenyl-propionic acid.' 258, eight and twelve lines from top, for ' Lohr ' read ' Loew. ' 258, thirteen lines from top, for 'Lorsch' read 'Lossen,' 326, three lines from bottom, for 'Monatsch.' read ' Monatshefte.' 364, in several places, for ' Stadelmann ' read ' Stadelraann.' 471 reference omitted to paper by Michael Foster ' On the existence of Glycogen in the tissues of certain Entozoa.' Proceedings of the Royal Society, Vol. 14 (1865), p. 543. BOOK II. THE PHYSIOLOGICAL CHEMISTRY OF DIGESTION. G. CHAPTER I. INTRODUCTORY REMARKS ON THE ALIMENTARY JUICES GENERALLY. SALIVA AND ITS ACTION UPON FOOD. Introductory Observations. Digestion is the process whereby the constituents of the food are rendered soluble and converted into bodies which are capable of absorption. These constituents are in part mineral, and of these the chief undergo no important chemical change prior to absorption. The larger part consists, however, of complex carbon compounds, which are for the most part insoluble in Avater when ingested, and which, after suitable mechanical processes of division and trituration, are subjected to the action of certain digestive juices which dissolve them and render them diffusible. The diges- The juices above referred to are produced in, or tive juices the by the agency of, the epithelium cells lining the products of interior of the glands which are either situated in the glands"^ walls of the alimentary canal or which empty their secretion into it. Although these cells derive the ma- terials necessary for their metabolic activity from the blood, the substances which they elaborate, and which are characteristic of the secretion which they help to form, are not found in the blood, but are the products of the activity of the protoplasm of the oells themselves. Enzymes or The characteristic constituents of the several juices ferments of which are specially concerned in the chemical changes the alimentary ^f the alimentary canal are certain so-called 'unor- canai. ganised ' ferments, which we shall, following the sug- gestion of Kiihne, denominate Enzymes. These are capable, like other ferments, of initiating, imder suitable circumstances, specific changes in certain bodies with which they are brought into contact, changes which may be incommensurably great when contrasted with 1—2 4 CLASSIFICATION OF FERMENTS. [BOOK II. the magnitude of the mass of the ferment engaged. These specific actions of ferments lead to the breaking down of complex into simpler molecules, the decomposition being necessarily associated with the conversion of some potential into kinetic energy, which usually appears as heat. ' Unorganised,' or as they have also been called, ' unformed ' ferments differ, however, from the ' oi'ganised' or 'formed' ferments in that, whilst they are the products of the activity of living proto- plasm, they cease, after being formed, to have any necessary connec- tion with organised forms, and have no power of reproduction or increase. Certain enzymes exert their action unimpaired in the presence of certain bodies which act as poisons to and kill the great majority of organised ferments ; thus salicylic acid and thymol, in not too great quantity, do not hinder peptic and tryptic digestion, but prevent the putrefactive changes which are very apt to occur in the latter case, and which depend upon the development of organised ferments. Certain enzymes, however, as the diastase of malt, or as the diastatic enzymes of saliva and pancreatic juice, are destroyed by salicylic acid. Changes in As will be shewn in detail in the sequel, the secret- secreting cells jj^g (,gjjg Q^ glands which produce enzymes exhibit to"^^variatiaQs ""marked differences or variations which correspond to in the func- different states of activity. In the case of the secreting tionai activity cells of the pancreas, as was discovered by Heiden- of organs. haiu, the cells appear to produce and store up for a time a body, a so-called 'zymogen,' from which an enzyme called ' trypsin ' is set free ; similarly, as the researches of Ebstein and Gilitzner, Langley and others have shewn, the secreting cells of the gastric glands produce in the first instance an antecedent of pepsin which we may term 'pepsinogen.' There is further reason to believe that the rennet-ferment has a corresponding zymogen. The progress of research will probably reveal the ex- istence of zymogens in relation to other animal enzymes. Enzymes or Usually the glandular organs which produce the their -zymo- digestive juices contain stored up w^ithin them during presenTki the ^^® periods in Avhich they are actively secreting their secreting characteristic enzymes or their zymogens ; these may structures be extracted by digesting the comminuted organ in which form water, weak spirit, chloroform-water or still better in em an may g^y^gj-jj^^ which dissolves them nearly all, and furnishes therefrom. solutions which preserve their activity long unimpaired \ 1 In reference to the solubility of enzymes and zymogens in glycerin, Mr Langley has furnished me with the following note : — ' I do not think it proved that ferments or zymogens are soluble in pinv strong glycerin. If they are soluble it is extremely slowly. If the oesophagus of a pig be dried and put in pure glycerin, in a well- stoppered bottle, it does not give one-sixtieth of its ferment (counting zymogen as CHAP. I.] NATURE OF ENZYMES. 5 Enzymes are all insoluble in strong alcohol, so that the tissues from which they are to be extracted, having by mechanical means been reduced to as fine a state of division as possible, may be first de- hydrated by placing them in absolute alcohol, and afterwards ex- tracted with glycerin or other suitable solvent. The treatment with alcohol has for its object the rendering insoluble of proteids which would otherwise dissolve in the liquid employed for the extraction of the ferment and thus furnish a less pure solution. Solutions of enzymes are, for the most part, rendered instantane- ously inactive by boiling; exposure to a temperature of 70° C. also destroys their activity, though less rapidly, and prolonged heating at lower temperatures exerts the same effect, though the lower limit, which doubtless varies in the case of the different enzymes, has not yet been ascertained. Nature of It has already been stated that under the influence the action of enzymes, the complex organic bodies which are exerted by susceptible to their action are decomposed, complex fin 5t vm ftR . . X ' ± breaking up into simpler molecules. These ferments appear to possess the power of rapidly inducing, at the temperature of the animal body, chemical changes in bodies subjected to them which are similar in character to those which are brought about with great slowness by prolonged heating with dilute mineral acids, or by the prolonged action of boiling water or of superheated steam. These operations are of the nature of ' hydrolytic ' decompositions, that is to say, such as are connected with the union of the elements of water with the body undergoing decomposition (see Yol. i. p. 19). A complete treatment of the theory of ferment action, or rather an account of the views which have been held at various times in regard to the action of ferments, though of great interest to the student of scientific history, would require too lengthy a discussion. The subject is one, however, which cannot be passed over without some remarks. The modern scientific history of ferments and their actions commences with the researches of Payen and Persoz^ on Diastase, and those of Cagniard-Latour^, and afterwards of Theodor Schwann^, on Alcoholic Fermentation. Three principal hypotheses have been propounded to account for ferment action : — of these the two first are still appealed to, to explain ferment) after a week. When a tissue has been ground it is impossible to separate the particles from the glycerin, and the particles of the pancreas pass readily through the finest filter paper. In most cases the glycerin extract has been simply strained through linen ; sometimes it has been filtered, but then it is doubtful whether sufficient care has been taken to prevent the dilution of the glycerin ; in dilute glycerin it is probably the water (or dilute salt solution) which is the solvent.' ^ Payen et Persoz, ' Memoire sur la Diastase,' Annales de Chimie et de Physique, Vol. 53 (1833), p. 73. ^ Cagniard-Latour, ' Memoire sur la Fermentation Vineuse, presente a I'Academie le 13 Juin, 1837,' Annales de Chimie et de Physique, Tome 68 (1838), pp. 206—221. ^ Schwann, ' Vorlaufige Mittheilung betreffend Versuche iiber die Weingahrung und Paulniss,' Poggendorff's Annalen, Vol. 41 (1837), pp. 184—193. Eefer also to his ' Microscopic Eesearches, &c.' Sydenham Society, 1847, p. 190. 6 THE THEORY OF 'CATALYSIS* OF BERZELIUS. [BOOK II. the actions of unformed, whilst the tliird has exclusively reference to formed ferments. 1. The contact or 'catalytic' theory of Berzelius. 2. The modification of the catalytic theory formulated by Liebig. 3. The physiological theory, which now holds undivided sway and which owes its commanding position to the splendid researches of Pasteur. This theory considers every ferment process to be the resultant of the activities of a definite organism. __ .. , There are certain chemical reactions which occur between Tne theory of . , ,■ i • i i e i • i ' Catalysis ' of ^'^^'^ bodies, in which the presence or a third exerts a Berzelius. remarkable influence, without the third body appearing on superficial examination to be modified by the process which it has helped to bring about. When, for instance, mixtures of hydrogen and oxygen find themselves in the presence of finely divided platinum, the two gases combine, under certain circumstances, with explosive violence. Again, when platinum black is brought into contact with the vapour of alcohol, the latter is oxidised and acetic acid is formed. To cite a third case, when peroxide of hydrogen, H,,0„, is treated with platinum black, that very unstable compound breaks up into water and oxygen, it being obvious that in this case two molecules, at least, of the peroxide must be concerned, its results being the formation of two molecules of water and a molecule of oxygen. As was discovered long ago, not only is this remark- able reaction brought about by platinum and certain other inorganic bodies, but also l)y certain organic substances. A shred of fibrin, for instance, or a droj) of blood, or of a solution of hsemoglobin will suffice to decompose a large quantity of a solution of hydrogen peroxide, which is thrown into efiervescence and rises in temperature. Berzelius was the first to bring together, and draw attention to, these remarkable phenomena, which he distinguished as ' catalytic ' and ex- plained as due to the action of a hitherto unrecognised force, to which he ascribed the term 'catalytic force'.' ' It is then proved,' he remarked, ' that several simple and compound, soluble and insoluble, bodies, are capable of exerting upon certain other bodies an action which is very difterent from that of chemical affinity. By this agency they are the means of producing in those bodies decomposi- tion of their elements, and subsequent rearrangements of the same without they themselves taking a part in them. ' This new force, which has hitherto been unrecognised, is common to organic and inorganic nature. I shall, therefore, call this force catalytic force. I shall, similarly, call catalysis the decomposition of bodies through the agency of this force.' Amongst the most obvious examples of catalytic phenomena, Berzelius classed the actions of ferments, both formed and unformed. In criticising the theory of Berzelius we must appreciate that its essence consisted in the hypothesis that the catalysing agent remained absolutely passive, whilst no attempt was made to shew in what manner this remarkable ' BerzeUus, ' Quelques idees sur une nouvelle force agissant dans les combinaisons des corps organiques.' (Annales de Chimie et de Physique, Tome 61 (1838), pp. 146 — 151). CHAP, I.] LIEBIG'S views OF ' CATALYSIS.' 7 contact action of the catalysing body operated. In the case of the most striking catalytic actions to which Berzelius drew attention, the progress of research has utterly disproved the passive part of the catalysing agent. The occlusion of gases by metals, for instance, is a process in which un- stable molecular compounds are formed, and it plays, no doubt, a most important part in the cases where finely divided metals bi-ing about the combination of gases. In these cases easily dissociated compounds are doubtless formed, and both the heat generated at the time of combination and the ease with which the newly-formed compound splits up with variations in temperature furnish the conditions which are necessary for the so-called catalytic processes. There are obviously a variety of types of so-called catalytic processes. Essentially they are all processes in which are concerned, as the principal factors, bodies of which the constituent atoms and molecules are in a state of virtually unstable equilibrium. An apparently insignificant variation in the conditions under which they exist is sufficient to lead to a rearrange- ment of the molecules of which they are composed and to chemical trans- formations of the most striking characters, often associated with transfor- mations of energy which are even more startling. To conclude, however, that the catalytic agent, which has furnished the energy which has as it were exploded the mine, remains actually passive, is to embrace a hypo- thesis which is opposed to all analogy. The conception of a catalytic force absolutely indefinite in nature, and displayed by a body whose function is active but whose transformations ai'e none, is, as suggested by Hiifner', neai-ly akin to the adoption of the conception of a vital force to explain obscure phenomena beyond the reach of actual knowledge. The doctrine of catalysis embodied, however, conceptions which are opposed to great and immutable principles. The true and, as it appears to the author, the really philosophical conception of the processes of catalysis was admirably set forth by the great J. R. Mayer. 'We call a force catalytic,' says the philosopher of Heilbron, 'when it holds no commensurable proportion to the assumed results of its action. An avalanche is hurled into the valley a pufi" of wind or the fluttering of a bird's wings is the catalytic force which has given the signal for, and which is the cause of, the widespread disaster".' The theory of catalysis of Berzelius possessed the sole merit of calling attention to a previously unstudied group of phenomena, which however it attempted to explain in a manner which did not tend to throw any light upon them. Lleb'e's mo Liebig^ modified the Berzelian theory, especially in dificatlon of reference to the ferments, by supposing that a ferment is tlie theory of invariably a body in a state analogoiis to, if not identical ' Catalysis.' with, decomposition, and that in virtue of the changes which it is itself undergoing it is able to bring about changes 1 Hiifner, ' Zur Lekre von den katalytischen Wirkungen. Erste Abtheilung, 1. Ueber die geschichtliche Entwiekelung des Begrifis.' Journal/, prakt. Chemie, Vol. 10, 1874, p. 148. 2 J. E. Mayer, Mechanik der Wdrme, 1867, p. 91, quoted by Hiifner. The author has been unable to verify this reference. 3 Liebig, J. v. ' Eechtfertigung der Contact-Theorie.' Annalen, Vol. 36, (1840), pp. 161 — 171. lb. 'Ueber die Gahrung und die Quelle der Muskelkraft.' 8 MODERN VIEWS OF ' CATALYSIS.' [BOOK 11. in the bodies subjected to its action. According to him, then, the body undergoing fermentation is, in a sense, inductively acted upon by the ferment, but the induence of the h\tter is a fortuitous one. Liebig believed the ferments to be essentially albuminous bodies, wliich acquire their fer- ment activities in virtue of their pi-oneness to decomposition, which is so great a characteristic of these bodies in the pi-esence of moisture and a suitable temperatui-e. By this hyiwthesis, Liebig sought to explain the action of the formed, as well as of the unformed ferments, believing that the processes of lite which ai-e chai-acteristic of the former led to the pro- duction of the very unstable substances, whose further puti-efactive decom- position he held to constitute the first stage of any pivx^ess of fermentation. There was, it will be i-emarked, a belief in the accidental, the for- txiitous, nature of ferment actions which inspired this theory of Liebig's. It partook of the spirit which pervade*.! theories of generation before the days of Redi and Spallanzani. In a sense the view of Liebig appears even more iriittional than that of Berzelius, for it assumes a fortuitous behaviour on the pan of bodies whose constancy of behaWour under a:iven conditions is a leading characteristic. Thou£:h advanced bv one whose extraordinary services in the development of modern chemistry cannot be gainsaid, the theory of Liebig was in opposition to a gi-eat number of facts already ascertained at the time when it was promulgated, and the erroneous statements upon which it was based tended more to delay than to funher the pix>gress of science. Whilst the splendid researches of Pasteur' at once shewed how far removed ai-e pix)cesses of fermentation from the category of fortuitous events, and that every true ferment action which is in any way connected with the changes of a li%"ing organism is to be looked upon as the resultant of the chemical acti\"ities of that organism. othei'S were proving the groundlessness of other of Liebig's arguments. In a masterly memoir*, Dumas, inter aUa, dealt with the physical theory which lay at the very foundation of Liebig's theory, to wit, the possibility of transmitting the state of activity engendered by specific ferments through media which are not pervadetl by them. Research soon followed research, which shewed that whilst it is diificult to free the unformed ferments from the proteid bodies which constitute the gixtund matter of the cell protoplasm in which they are formed, there are but slender grounds for coming to the con- clusion that a ferment is essentiaUy a proteid, much less a proteid in a state of decomjx)sition. Have then the more accurate and correct \"iews of catalytic phenomena to which the progress of science has introduced us enabled us to form any conception as to the way in which an unformed ferment may exert its action? To this question we may reply that amongst the phenomena wliich used formerly to be explained on the mere hypothesis of ' catalysis,' there are some which are suggestive of the kind of interchanges which probably go on between the above ferments and the bodies of which they eflfect the decomposition. ^ Pasteur. The student will find it most convenient to read the summary of the very numerous researches in this department of knowledge of this great scientific man in his work entitled -Etudes sur la Biere.' Paris, Gauthier-Villars, 1876. - Dumas. • Recherches sur la fermentation alcooliqne.' Comptes Rendws det stances de VAcademU des Sciences, T. 75, 1872, p. 276. CHAP. I.] CIKCUMSTANCES AFFECTING ENZYMES. 9 It appears almost certain that amongst catalytic phenomena, employing the term in the sense in which J. E,. Mayer employed it, fei-ment pheno- mena resemble those in which there is apparently a periodic synthesis and dissociation of the catalysing agent, which acts in a similar manner to the agent which explodes a train of gunpowder. Amongst chemical phenomena in which one body acts apparently as a go-between, and leads to an almost indefinite series of exchanges of matter and energy, two at once suggest themselves to the mind of the thinker as afibrding a clue to the probable action of ferments, to wit : (1) the function of haemoglobin as an oxygen carrier, as a go-between the atmospheric oxygen, on the one hand, and the organic molecules which are oxidised by it in the organism, on the other, and (2) the function of sulphovinic acid in the process of eetheri- fication. In the latter case, however, the results of the process are the reverse of those which follow the normal action of ferments, in so far that whilst the latter as their pi-imary function lead to the decomposition of complex into simpler compounds, the action of sulphovinic acid leads to the synthesis of a more complex out of simpler molecules, to a conversion of kinetic into potential energy. Enzymes The principal enzymes of the alimentary canal differ in their belong either to the group of ' proteolytic,' or to that of actions. ' amylolytic ' ferments. The enzymes of the first group (pepsin and trypsin), dissolve proteids and effect their more or less profound decomposition. The enzymes of the second class (as the so- called ' ptyalin,' the diastatic enzyme of the salivary glands, and the powerful diastatic enzyme of the pancreas) liquify boiled, gelatinous starch, breaking down the complex starch molecule into molecules of greater and greater simplicity, of which the final representatives are a dextrin, maltose and dextrose. In addition to the two groups of ferments referred to above, there occur in the alimentary canal ' curdling,' * inverting,' and ' fat-decom- posing ' or ' piolytic ' ferments. These enzymes will be considered in detail in the sequel. Circum- i- Temperature. All enzymes exert a more ener- stances wMch getic action at a moderately high than at a low tempe- influence the rature, though the influence of a rise in temperature is activity of more marked in some cases than in others, ii. Reaction. tnzymes. rpj^^ reaction of the medium in which they are placed, influences remarkably the activity of certain enzymes ; thus the proteolytic enzyme of the stomach, pepsin, is inactive in neutral or alkaline solutions, the presence of a free acid being essential to its activity ; whilst the proteolytic ferment of the pancreas, trypsin, acts with feebleness in solutions which are neutral or feebly acid and needs a decidedly alkaline medium for the full exercise of its powers, iii. Presence or absence of excess of certain salts. The influence exerted by salts upon certain reactions induced by ferments is illustrated, (a) by the impossibility of inducing the curdling of casein in the absence of calcium salts. (6) by the hindering action exerted by certain neutral salts on the coagulation of the blood, and of certain 10 PURPOSES SERVED BY SALIVA. [BOOK II. other salts, as for instance, potassium iodide and bromide on peptic digestion. In exerting From a consideration of all the facts bearing on the their action matter it would appear that in exerting their character- are enzymes ^gj.^^ actions the various enzymes are in part slowly and gradually destroyed, so that the activity of a given quantity of enzyme cannot be prolonged indetinitely. In most, perhaps in all, cases the accumulation of bodies which result from the ferment action slows and ultimately stops that action long before the enzyme has been exhausted or destroyed, so that, by merely removino: the bodies so actinor, activity is restored to it. This re- moval can often be etfected by the process of dialysis. Sect. 1. Saliva, and its Action upon the Constituents of Food. ISTRODUCTORY SKETCH, CHIEFLY COXCERXIXG THE SALIVARY GLAXDS. Purposes The interior of the mouth is continually moistened served by by a somewhat viscous, tasteless, watery liquid, the saliva. saliva, a product of the activity of several so-called salivary glands ; the presence of this liquid facilitates the movements of the tongue, lips and cheeks in articulation. Though essential to proper articulation, the saliva is, however, to be looked upon as one of the digestive juices, and is poured out in much increased quantities when food is introduced into the mouth. It acts as a solvent of many sapid substances introduced into the mouth, and as the vehicle which brings them into contact with the end organs of the nerves of taste ; by moistening the food it ren- ders the essential preliminary act of mastication more easy; it prevents the particles of food from adhering to the interior of the mouth, and thus co-operates with the muscular movements of the lips, tongue, and cheeks in forming the crushed food into a bolus which may readily be propelled through the pharynx and oesophagus; lastly, in man and several other animals it exerts, in virtue of the presence of an enzyme, which used formerly to be termed ptyaliu, and which we now usually term the ' diastatic ' or ' amylolytic ' ferment of the saliva, a solvent action upon the starchy constituents of food, and thus initiates the chemical operations to which the food is subjected in its progress thz'ough the alimentary canal. The saliva exerts, therefore, two sets of functions, the mechanical and the chemical, of which the first are unquestionably the more important, as is shewn by the fact that in many animals the saliva is free from diastatic enzyme and therefore from any chemical activity whatsoever, or contains it in such small quantities that they cannot be supposed to exert any appreciable action. CHAP. I.] STRUCTURE OF THE SALIVARY GLANDS. 11 GENERAL OBSERVATIONS UPON THE STRUCTURE OF THE SALIVARY GLANDS WHEN AT REST As has been already said, the saliva is secreted by several glands of which the ducts pour their secretion into the cavity of the mouth, where it is mingled and constitutes the 'mixed saliva.' The chief of these glands are the parotid, submaxillary, and sublingual glands, though their secretion is mixed with that of small glands {mucous and serous) scattered through the mucous membrane of the mouth and tongue, and which are included under the term of ' buccal ' glands. Many animals possess also a fairly large orbital gland, the duct of which opens into the mouth. structure of The salivary glands all belong to the group of the salivary ' acinous ' or ' compound racemose ' glands, although glands. i)^Q terminal alveoli are in reality more tubular than spherical. According to the researches of Heidenhain they may, however, be divided into two groups, which he has denominated serous, or albuminous, and mucous glands, according to the structure of the cells of their acini, their chemical characters, and the nature of the secretion which they elaborate. The parotid gland is, in most, if not in all, mammals, an albu- minous gland, although a few mucous cells may be present in it. The submaxillary gland is in some animals albuminous, as in the rabbit : in others mucous, as in the dog : in others, again, part albuminous and part mucous, as in man. The sub-lingual gland consists in part of tubes with mucous cells and in part of tubes with albuminous cells ; on account of the general preponderance of the mucous element it is classed with mucous glands. The orbital gland is as a rule mucous or serous according as the submaxillary gland is mucous or serous. Glands belonging to the former of these classes secrete a fluid containing some, though it may be only a small, quantity of a proteid coagulable by heat, and resembling, if not identical with, serum-albumin; the mucous glands, on the other hand, as their name implies, secrete a liquid relatively free from albumin ; but containing mucin as its characteristic constituent. In the serous glands hardened in alcohol the epithelium lining the acini is composed of comparatively small, polygonal or rounded cells, of which the outlines are not very distinct until acted upon by certain reagents ; the protoplasm, which is but slowly coloured by carmine, presents many dark granules, and the normally spherical nucleus is often shrunken by the reagent. In the mucous glands the characteristic (mucous) cells of the alveoli are large and clear, very faintly granular, with a rounded or oval nucleus near their periphery surrounded by a little protoplasm. Here too the nucleus may be much shrunken. The part of the cell near the nucleus is usually prolonged into a process which overlaps the neighbouring cell. 12 MICRO-CHEMICAL REACTIONS OF GLAND CELLS. [BOOK IL In addition to the characteristic mucous cells there are found in the alveoli of some mucous salivary glands when examined in a state of rest, situated at some parts of the perij^hery, i.e. lying more internal than, or nearer to, the membrana propria than the mucous cells, small cells, possessed of a round nucleus usually aggregated together, and containing much albumin ; to these aggregations (first described by Gianuszi^) the term demilunes or liimilw has been applied. They may with probability be regarded as albuminous cells which have been overlapped by the larger mucous cells. Microche- ^' "^^^ serous cells possess micro-chemical reactions micai reac- which indicate the presence within them of proteids; tions of the to wit, the addition of dilute mineral acids (containing serous and q.q2 per cent, of acid) causes marked turbidity, an mucous ce s. ggg^t which is much more strongly produced by the same acids in a concentrated condition. Acetic acid causes con- siderable swelling and a clearing up of the cell contents. 2. Mucous cells appear to be composed mainly of mucin or mucigen ( ?). Their substance is precipitated by acetic acid, whilst it is altogether unacted upon by strong mineral acids. 3. According to Nussl)aum" the presence of amylolytic ferment within the secreting cells of the salivary glands is rendered eviflent by the cells assuming a dark colour when brought in contact with a 1 per cent, solution of osmic acid. It has however been shewn by Griitzner^ that the cells of salivary glands, which form no diastatic ferment, as for instance the submaxillary gland of the rabbit, possess the property of reducing osmic acid. Langley^ has shewn that if a judgment as to the cells which form diastatic ferment were based upon the osmic acid reaction, we should be led to the absurd conclusion that the ferment is chiefly formed by the epithelium lining the ducts and ductlets and the part of the alveolus next to the latter, whilst the alveolar cells proper would enjoy no such function. Some glands As has been said, in certain mucous glands the intermediate mucous cells are supplemented by the cells of the demi- in structure. lunes, though certain mucous glands, as those of the tongue, exist where the typical mucous cells alone occur. There are glands, and the submaxillary of man is an example, which are termed mixed glands, inasmuch as some of the acini have all the characters of serous, others of mucous glands. 1 Gianuzzi, Ber. d. SiicJu. Ges. d. Wigs., Sitz. f. 27 Nov. 1867. - Nussbaum, 'Die Ferment-bildung in den Driisen.' Archiv f. micros. Anat. Vol. XIII. (1876), p. 721. 3 Griitzner, ' Ueber Bildung und Ausscheidung von Fermenten.' Pfliiger's Archiv, Vol. XVI. 1877, p. 10.5. ^ Langley, ' Some remarks on the formation of ferment in the submaxillary gland of the rabbit.' Journal of Physiology, Vol. i. (1878), p. 68. CHAP. I.] NERVOUS SUPPLY OF SALIVARY GLANDS. 13 The Nervous Swpply of the Salivary Glands. We shall not enter, in this place, into a detailed description of the innervation of any one of the salivary glands, but shall confine our- selves to the following categoric statements. Each salivary gland is supplied by at least three classes of fibres, viz. secretory fibres, vaso-constrictor and vaso-dilator fibres, of which the first and the third are in general conveyed to the glands in branches of cerebral nerves : these are, the chorda tympani for the submaxillary and sublingual ; and the auriculo-temporal (which how- ever derives them through communications with the otic ganglion) for the parotid. The second class, of vaso-constrictor, fibres for the most part run in sympathetic trunks, which, however, also contain secretory fibres. When therefore one of the cranial branches supplying a gland is stimulated, there occur two acts, viz. secretion'' and simultaneous dilatation of blood-vessels^ ; that these two acts are not absolutely interdependent is proved by the fact that certain drugs such as atropin^ paralyse the one set of fibres, leaving the other intact. When, on the other hand, the sympathetic filaments supplying the gland are stimulated, the blood-vessels of the gland contract, and there is produced a small quantity of saliva differing in physical characters and chemical composition from that obtained under the circumstances first referred to. Heidenhain's According to Heidenhain*, however, in each of the distinction be- two kinds of nerves supplying a salivary gland there tween secre- exist, besides the vascular nerve fibres, secretory and tory and tro- trophic, or as we should prefer to term them, 'metabolic' p ic nerves. fibres, though the number of one or other of these classes may be insignificant ; the secretory usually predominating in the cranial nerve branches, the trophic in the sympathetic. Stimulation of secretory fibres leads, according to Heidenhain, to an increased flow of water ; stimulation of the metabolic to an increased secretion of specific substances, in consequence of the conversion of insoluble into soluble substances, and to an increased production of protoplasm. There are decided objections to accejDting the term trophic (which has already been used in a different and fairly well-known sense) to designate those nerve fibres whose action it is specially to increase the metabolism of secreting cells, and we shall therefore in general use metabolic in the same sense as Heidenhain's expression trophic. The term trojyhic has been generally employed to designate the action which certain nerve 1 Ludwig, 'Neue Versuche iiber die Beihiilfe der Nerven zur Speichelabsonderung.' Zeitschr.f. rat. Mediz., N.F. (1851), p. 259. ^ Claude Bernard, Comptes Rendus, 28 Jan. 1858. ^ Kieuchel, 'Das Atropin u. die Hemmungsnerven.' Dorpat, 1862. ■* Heidenhain, 'Physiologie der Absonderungsvorgange.' Hermann's Handbuch, Vol. V. p. 55. 14 PHENOMENA OF SALIVARY SECRETION. [BOOK II. centi'es exert on the nerve fibres connected with them and on the tissues and organs Avhich are innervated by thera. Thus the Gasserian ganglion is said to exert a trophic influence on the eye, as its complete division leads in general to destructive changes in that organ; or to take a case less open to controversy, the ganglion on the posterior root of a spinal nerve is said to exert a trophic influence on the afferent fibres connected with it, because when these are separated from it, and so removed from its influence, they undergo a process of degeneration. Vasculai' Changes luhich accompany Secretion. Ordinarily when a salivary gland passes from the state of rest into that of activity it is at once the seat of an increased blood-flow, which is associated with the dilatation of the blood-vessels of the organ. Under these circumstances the blood leaving the gland presents a florid arterial, instead of a venous colour, which characterises that of the organ when at rest. This vascular dilatation is explained by the coming into action of the before-mentioned vaso-dilator fibres ; it is not necessarily dependent on the act of secretion, as it may occur after the secretory fibres have been paralysed. Heat evolved during Secretion. As was shewn in a now classical investigation of Ludwig\ when the salivary glands are thrown into activity there is a rise in tem- perature, so that the temperature of the saliva leaving the sub- maxillary gland may exceed by 1" C. that of the blood flowing to the gland. This rise in temperature cannot be explained by a study of the chemical characters of the salivary secretion, but is doubtless the result of the increased metabolic changes which neces- sarily accompany the act of secretion in the gland cells, and which chiefly affect their protoplasm. The Secretion of Saliva not an act of filtration. That the secretion of saliva (and indeed that secretion in general) is not a mere act of filtration, was proved by Carl Ludwig when he shewed that saliva can be secreted by a gland though the pres- sure exerted by the secreted fluid in the ducts within it is considerably higher than that of the blood circulating through the arteries which supply it. On many grounds it may be positively asserted that the secreting cells are the primary agents in the withdrawal from the blood of the water necessary for the secretion, though the exact nature of the process is yet unknown'; similarly on the grounds stated below we know that within the protoplasm of the gland cells the characteristic soluble constituents of the secretion are formed. 1 Ludwig u. A. Spiess, ' Vergleichung der Warme der Unterkiefer-Driisenspeichel und des gleichzeitigen Carotidenblutes.' Zeitschr.f. rat, Med., 1858, p. 361. - Consult Heidenhain, Hermann's Handhuch, Vol. v. p. 72. CHAP. I.] CHANGES IN GLAND CELLS DUEING SECRETION. 15 Structural Changes in Secretory Cells accompanying activity of the Salivary Glands. The researches made during the last few years by Heidenhain, Ebstein and Griitzner, Langley, and fully confirmed by a large number of observers, have demonstrated that in the salivary glands, as perhaps in all secreting glands, structural and perfectly obvious microscopic changes occur, which stand in close relation to the different conditions of functional activity. The resting gland cell is large, but possesses compa- of restmg^" ratively little protoplasm, and therefore comparatively glands. little matter which can be stained by colouring matters, especially by carmine ; it contains, instead, a store of material which has been elaborated in, or at the expense of, the protoplasm. This material does not constitute the specific matter of the secretion, but is its antecedent. That a chemical difference exists which admits of direct proof is argued by Heidenhain, in the case of the mucous glands for several reasons, but mainly on the ground of the statements of Watney and Klein, that whilst mucin is stained by hsematoxylin, its antecedent (mucigen) is not affected by that colouring matter. Mr J. N. Langley, who has devoted much attention to this question, has arrived at the conclusion that as yet no evidence what- ever exists which warrants the assertion that such a hypothetical mucigen exists. In a hitherto unpublished note on the subject which the author has had the advantage of reading, he points out, inter alia, that hsema- toxylin when added to saliva does not stain the mucin which that fluid contains, unless it be in a solution which contains alum. The behaviour of the gland cells towards ha3matoxylin varies greatly according to the treatment which the tissue has imdergone. Langley has frequently obtained sections of gland hardened in alcohol with a stringy mass of mucin in the ducts, and on staining with hsematoxylin (whether Kleinenberg's, or Bohmer's or Delafield's, or in aqueous solution, or in dilute alkaline solution), obtained good staining of nuclei and demilunes without the mucin having taken a trace of colour. If we are to rely on the hsematoxylin test we must, in such cases, conclude that the saliva in the duct did not contain mucin but mucigen. ' It is possible,' says Langley, ' that a method of staining with hsematoxylin may be found which shall give satisfactory results ; for sometimes the substance in the duct is stained more than the cells and sometimes the cells are unequally stained, but at present one cannot use hsematoxylin in such a way as to give such results constantly.' But Langley's criticism is not limited to the chemical grounds which have been alleged in favour of the hypothetical mucigen. He considers that the physiological evidence in favour of its existence is at present insufficient. The further discussion of this question is beyond the scope of the present work. Characteris- When, however, a gland passes into a state of tics of glands activity, as for example by the irritation of its so-called in a state of secretory nerves, the gland cells undergo the following activity. changes, which may proceed simultaneously, though 16 MIXED SALIVA. [BOOK II. not necessarily so : — the stored-up matter previously referred to is converted into soluble constituents of the secretion, and at the same time there occurs a growth of the protoplasm of the cells, at the expense doubtless of the richer supply of lymph -which, during the secretory act, bathes the gland. The period of activity in so far as the gland cell is concerned is indeed a period of removal of ready-made constituents of secretion; a period in which the protoplasmic constituents of the cells generally increase. According to some, active proliferation of secreting cells occurs ; the latter statement is probably incorrect. Whilst we have in a few sentences sketched the general characters of the changes which glands undergo during secretion, our picture is wantingr in all details, and the reader is referred for further infor- matiou to works on Histology and Physiology'. Sect. 2. The Chemical Composition of Mixed Saliva, of the SECRETION of THE THREE CHIEF SaLIVARY GlaNDS, AND OF Buccal Mucus. 1. Mixed Saliva. Mode of Ob- The mixed saliva of man may be obtained in a state taining mixed of purity, some hours after a meal, by everting the lower saliva. \{p depressing the head, and collecting the clear liquid which slowly trickles from the angles of the mouth. An abundant flow of saliva may be provoked by the internal use of Jaborandi or its alkaloid Pilocarpine. A fairly copious flow may be obtained by inspiring, through the mouth, the vapour of chloroform, or by washing out the mouth with water containing a little ether in solution, or even by chewing a fragment of rhatany root ; in the latter case the fluid is naturally mixed with the vegetable fragments, and with the soluble constituents of the drug. Quantity of In the case of saliva, as in that of other digestive saliva secre- juices, we possess no mode of determining in a reliable ted by man. manner the amount of the secretion which is poured out in the physiological condition. Mitscherlich calculated the probable secretion of mixed saliva to amount to 8 to 10 ozs. daily. According to Tuczek^, the salivary glands of adult man secrete ' Consult specially Heidenhain's systematic account under the heading ' Vorgange innerhalb der Driisen wahrend ihrer Thatigkeit ' in Hermann's Handbuch, Vol. v. Chapter iv. p. 56. The reader will find a more lengthy treatment than is possible in the present work in Dr Michael Foster's Text-Book of PJiysiology, Ed. v. 2 Tuczek, ' Ueber die von Menschen wahrend des Kauens abgesonderten Speichel- mengen.' Zeitschr.f. Biologie, Vol. xii. p. 534. CHAP. I.] MIXED SALIVA. 17 during mastication at the rate of 1300 grammes of saliva for each 100 grammes of gland-substance, the saliva containing 6*3 grammes of solid constituents, of which 3'9 grammes consist of organic matters. Physical Properties of Mixed Saliva. Normal saliva is, when perfectly fresh, a clear, transparent, viscid fluid, which on microscopic examination is found to hold in suspension, but very sparsely distributed through it, cells of squamous epithelium which have become detached from the walls of the mouth, besides certain cells denominated salivary corpuscles, which are probably leucocytes altered by the action of saliva ; these cells, which present some resemblance to leucocytes, are much more globular and contain within their interior granules which exhibit so-called Brownian movements in a very remarkable manner. Specific The specific gravity of the mixed saliva of man gravity. varies between 1'002 and 1"006, the mean being, how- ever, about 1'003. Reaction. Perfectly normal, human saliva possesses an alkaline reaction, which is least marked after a long fast, and most distinct when the flow of the secretion is at its height. According to Chittenden and Smith the alkalinity corresponds to that of a solution containing 0"08 per cent, of '^o.^CO^^. In some persons, especially in the morning, the saliva is found to possess an acid reaction, which is however due to fermentative changes. Frerichs^ found that 100 grammes of saliva secreted by himself, during smoking, required 0"150 grammes of sulphuric acid to neu- tralise it. TEE CHEMICAL CONSTITUENTS OF MIXED SALIVA. Water. As is indicated by its specific gravity, saliva is a very watery liquid, containing only from five to six parts per mille of solid constituents. The Organic Solids of Saliva. Proteids The solids consist partly of undissolved, suspended, and mucin. organic matters, especially epithelium, and partly of dissolved organic matters and salts. They always contain a very small quantity of a soluble proteid, which resembles, if it is not identical with, serum-albumin, besides a considerable quantity of mucin. Biastatic In the case of the saliva of man and certain other enzyme. animals, an enzyme is present which possesses amylolytic properties and exerts a chemical action which appears to be identical 1 Chittenden and Smith, Transactions Connecticut Association, 1885. ^ Frerichs, Article ' Verdauung,' Wagner's Handworterbuch der Physiologie, Vol. II. Part i. p. 760. G. 2 18 CONSTITUENTS OF MIXED SALIVA. [BOOK II. with that of diastase. This ferment has frequently been termed Pti/alin, though this name was originally applied by Berzelius' to the organic matters of the saliva generally, obtained by a method which robbed them of all ferment action, which besides was unknown to the Swedish observer. It is more usual to designate it the Diastatic Ferment (or Enzyme) of the Saliva, or Salivary Diastase. It will be separately discussed in one of the succeeding sections. By V. Wittich's method, Hiifner^ obtained from the and Munk's salivary glands of the pig a glycerin extract which, in discovery of a addition to very slight diastatic, possessed feeble but proteolytic decided, proteolytic activity. This ferment was said ferment in ^^ ]^q active in alkaline as well as in acid solutions, saliva. Munk^ obtained a similar ferment from mixed saliva, but found that it was very active in acid solutions. It is probable that the ferment discovered by both Hiifner and Munk was pepsin, of wdiich minute traces probably make their way into the several fluids of the body. The urine, for instance, is known to contain a trace of diastatic ferment and especially of pepsin, and occasionally, it is said, of trypsin, and of rennet ferment*. Extractive In disease, certain extractive matters, such as urea, matters of leucine and lactic acid, have been discovered in the saliva. saliva. The first of these is probably a normal con- stituent, though only present in minute traces. We do not yet know what other extractives occur as regular constituents in health. The Saline Constituents of Saliva. The Saline Constituents of the Saliva are composed chiefly of alkaline chlorides ; they include, however, also alkaline and earthy phosphates, and, in some cases, earthy carbonates. They are distin- guished by the presence of a salt whose formation appears character- istic of the salivary glands, viz., a soluble sulphocyanate. Discovery Treviranus' was the first to observe that when a of a suipho- solution of ferric chloride is added to saliva it produces cyanate in ^ reddish colour, w^hich was subsequently conclusively shewn by Tiedemann and Gmelin® to be due to the presence of sulphocyanic acid in saliva. 1 Berzelius, Traite de Chimie. Nouvelle Edition par Valerius (1839), Vol. iii. p. 591. ^ Hiifner, ' Untersuchungen iiber die ungeformten Fermente.' Journ. f. prakt. Chemie, New Ser. Vol. 5, p. 372. ^ Munk, 'Untersuchungen iiber die ungeformten Fermente im Thierkorper.' In Maly's Jahresbericht, Vol. 6, p. 270. * W. Sahli, 'Ueber das Vorkommen von Pepsin und Trypsin im normalen mensch- lichen Harn,' Pfliiger's Archiv, Vol. 36 (1885), p. 209^. A. Stadelmann, 'Ueber Fermente im normalen Ham,' Zeitschrift f. Biologic, Vol. 24 (1888), p. 226; also ' Untersuchungen iiber den Pepsin-Ferment-gehalt des normalen und pathologischen Harnes.' Zeitschrift/. Biologie, Vol. 25 (1889), p. 215. 5 Tre-^-iranus, Biologic, 1814, Vol. iv. p. 330. ® F. Tiedemann und L. Gmelin, Die Verdauung nach Versuchen. Heidelberg u. Leipzig, 1826, Vol. i. p. 8, et seq. CHAP. I.] PKESENCE OF SULPHOCYAXATES IN SALIVA. 19 Mode of de- (<^) Human saliva is treated with a small volume of monstrating a pale and acidulated solution of ferric chloride. A presence of a reddish colouration of varying intensity, but tending to suiphocyanate ^-^^^ ^^ diluted claret, is generally produced. This 111 S3.11V3. ' O «/ i colour is bleached by the subsequent addition of a solution of corrosive sublimate. (b) According to Gscheidlen's ' method, filter-paper is dipped in a weak solution of ferric chloride containing some free hydrochloric acid and then allowed to dry. The contact of a drop of saliva with such paper occasions a reddish stain. The author can strongly recommend this method. (c) Soleras Reaction. When human saliva is treated with a solution of iodic acid it assumes a yellowish colour, due, according to Solera^ only to the sulphocyanate present, which liberates iodine; the latter is subsequently easily detected by the addition of starch. This reaction is said to permit of the detection of 0 00000004 grm. of a sulphocyanate. Is a suipho- A sulphocyanate is not constantly present even in cyanate con- human saliva. According to Hoppe-Seyler, with whose stantiy pre- experience on this matter that of the author does not coincide, it is indeed frequently absent^. In the saliva of the dog Hoppe-Seyler has never discovered a sulphocyanate, whilst both Schiff and Solera discovered it in the mixed saliva and in the secretion of the parotid gland. It has been asserted by Schiff that the quantity of a sulpho- cyanate, as determined by the depth of tint produced by the addition of an iron salt, increases after saliva has been secreted, but the state- ment appears to be inaccurate. Proportion According to Munk*, whose method of quantitative of suiphocy- analysis will be described in a subsequent section of anic acid in ^]^[g^ chapter, the proportion of sulphocyanic acid in ^ ^^' mixed human saliva amounts to O'Ol per cent. Constitution o n i • • i CN] a t. x-j. j.- j.i and probable oulphocyamc acid tt \io has a constitution exactly origin of sul- ^ r a o a to t^ CO 1 a o o o 1 ." Ci IH '3 r5 (£4 fj r/^ S P t_- o a 0) li do w p p 1 1 a o o 6 Ci r-H p GO H^ Ci C-1 -^t* tr- ' ' ^ ip -* ii r^ CO > 2 C5 ^ 00 CO 1 in 00 K j 1 ^ 1 "^"i '^ t 1 1 op r-t -1h o O « CO «5 o C5 13 ja Oi u C o Pn e3 to /— ^'— . • ■? & *? •r -* 1 r— 1 (>1 S a| lb -^ r^ 1 (fl r^ C5 -§1 o "i* Sh' o -* -«*< 1 O • c® r-H CO '^ '-t- S Cl«-^ 1 o ?? CO fh CO CO Wta a eo O § ^ CO .-1 W _o C5 M o o 1) -fcS -kJ p CO p -• -s "^