118 
PRINCIPLES OF BACTERIOLOGY 
by heat; it is then stained for tubercle bacillus as de¬ 
scribed in the section on Staining. 
11. Animal Inoculation.—Very often when no evi¬ 
dence of tuberculosis can be found on examination of 
smears or cultures, animal inoculation has to be resorted 
to. 
The fluid to be injected (peritoneal, pericardial, pleural 
or cerebrospinal fluid) is centrifugalized and the sedi¬ 
ment is mixed with a few cubic centimeters of sterile 
salt solution, and 1 c.c. is injected into a guinea pig in- 
traperitoneally. If sputum is used, a suitable (yellowish) 
piece is rubbed up with salt solution, instead of centrif- 
ugalization. Four weeks later the guinea pig is killed 
and examined for the evidences of tuberculosis. If the 
animal dies before the time specified, autopsy is immedi¬ 
ately made. 
If the guinea pig is x-rayed for thirty seconds before 
injection ten or fourteen days are a sufficiently long 
period to wait (as x-raying destroys the lymphoid tis¬ 
sue which protects the animal against tuberculosis, and 
it is thus rendered more susceptible). 
If pneumonia is suspected, one c.c. of blood is injected 
intraperitoneally into a white mouse, and cultures and 
smears are made from the peritoneal fluid. 
It should be always borne in mind that the final re¬ 
sults depend on the care with which all manipulations 
are made, as the opportunities for contamination are 
great. Scrupulous care should be exercised in flaming 
the cotton stoppers before and after opening tubes and 
flasks with culture media, the platinum needles and 
loops, etc. Certain procedures can not be explained, but 
have to be seen in order to be grasped; the pupil can, 
however, learn at the outset the fact that care in handling 
the materials is more essential than speed. 
