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Full text of "Pathogenic Bacteria"

384                 PATHOGENIC BACTERIA.

In the absence of a satisfactory method of securing
definite small quantities of blood for immediate or sub-
sequent use, I was led to make some experiments with
capillary tubes to determine their possible value for the
purpose.

It is a well-known physical phenomenon that in clean
capillary tubes fluids are attracted to a height varying
according to the diameter of the tube and the density of
the fluid. In tubes of equal diameter the height of the
column is invariably the same.

Such tubes can be made by heating a piece of ordinary
glass tubing, such as is to be found in every laboratory,
in a Bunsen flame for a few minutes until it becomes red
and soft, removing the glass from the flame, and then
pulling upon the ends steadily and slowly until the tube
is drawn out to the desired diameter. The errors to be
avoided in making the tubes will be—heating too much
and making the glass too soft, drawing out the tube
while still in the flame, and drawing too rapidly. The
result of these erroneous methods will be that the tubes
are much shorter and finer than is desired. A few mo-
ments' practice will show just how the manipulation
should be done to secure the best results.

The fact was, however, established that tubes of about
the same diameter showed almost no variation in the
quantity of liquid contained. So little was the difference
in the length of the column and the weight of the con-
tained blood in tubes recognized by the eye to have uni-
form caliber that I have no hesitation in recommend-
ing an application of the capillary tube for securing
small measured quantities of blood for the specific typhoid
tests and similar experiments.

The application of the method is simple and consists in:

1.  Accurately weighing  the   amount  of blood   that
enters a capillary tube of a size arbitrarily selected as a
standard.

2.  The manufacture of a large number of tubes of the
same size.