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by dividing the volume of fat, obtained by analysis, in a given 
amount of milk by the number of globules which it contains. The 
first method requires somany accurate measurements and extended 
calculations that it is really impracticable. The latter demands an 
estimation of the fat and number of globules, but as nearly all inves- 
tigations upon milk requires a determination of the fat the count- 
ing of the globules is usually the only extra labor. The ordinary 
method of mounting liquids for microscopic examination, by placing 
a drop upon a glass slide and laying a thin cover glass upon it, 
cannot be used for this purpose, it being practically impossible to 
determine the volume of milk in a given field with sufficient ac- 
curacy. 
This difficulty may however be overcome by confining the milk to 
be examined within a space all of whose dimensions are known or 
easily determined. For this purpose a small capillary tube about 
one tenth millimeter in diameter is well adapted. 
This tube may be drawn from about ¢ inch tubing which should 
be round and have the sides of uniform thickness. It should be 
heated quite hot and drawn as nearly as possible in the direction of 
its length, so that the resulting capillary tube will be of uniform 
diameter, and round, not flat. ‘This is very essential, as any flatness 
in the tube used will greatly exaggerate the results. A flat tube can 
usually be detected by rolling between the fingers, but it is safer to 
measure its diameter in two or three positions with the microscope. 
The tube should be drawn straight, as a curved one is never quite 
round. With some one to assist, several feet may be drawn at once 
and, if successful, supply material for many determinations. 
The milk for examination must be largely diluted before it is 
placed in the tube, otherwise the globules will be so numerous and 
overlap each other to such an extent that it will be impossible to 
count them. For ordinary fresh milk a dilution to fifty times its 
volume (10 c. c. to 500 ¢c. ¢.) is about right. There are however 
some milks in which the globules are very numerous and very small 
where a greater dilution is desirable. Skim-milk should be diluted 
very much less, ranging from ten to twenty times its volume accord- 
ing as the separation of cream has been more or less complete. 
For mounting a sample of this diluted milk a capillary tube from 
2 to 3 centimeters long is taken and one end immersed in the liquid, 
when it fills immediately by capillary attraction. Both ends are 
then closed with a little soft wax or vaseline to prevent evaporation 
and movement of liquid in the tube. ‘T'wo or three tubes thus filled 
and sealed are laid upon a glass slide. A drop of glycerine is placed 
upon them and then over all a thin cover glass. After standing a 
short time in a level position they are ready for examination. It is 
best to place the slide immediately upon the stage of the microscope, 
which should be so arranged as to be level. Owing to their low spe- 
cific gravity, the globules will presently take a position along the 
upper side of the tube, where they may be readily brought into focus 
and easily counted. . Although it is best to count the globules as 
soon as possible after mounting, it may be deferred, if the tubes have 
been properly sealed and kept in a level position, for several hours, 
or even days, without materially affecting the number found. 
