114 EXPERIMENTAL DAIRY BACTERIOLOGY 



Examination for tubercle bacilli by animal inoculation. 



The inoculation of animals susceptible to tuberculosis is a 

 much more delicate test for the presence of tubercle bacilli 

 in milk than the microscopical examination of the sediment. 

 Highly virulent milk from a tuberculous animal may be di- 

 luted as much as a million times, and the presence of tuber- 

 cle bacilli in the mixed milk may be readily demonstrated by 

 animal inoculation. The guinea pig is used, being the most 

 susceptible of the experimental animals to artificial inocula- 

 tion, and very resistant to infection in a natural way. 



1. The unheated milk may be centrifugalized as for the 

 microscopical examination. Five cubic centimeters of the 

 mixed cream and sediment are injected into the abdominal 

 cavity. The syringe is filled with the mixture, the skin and 

 abdominal wall of the animal picked up between the thumb 

 and finger, and the needle of the syringe thrust through the 

 skin and wall at right angles to the body. The inoculation 

 should be made toward the side rather than in the median line 

 of the abdomen. Frequently the animals die in a short time 

 of acute peritonitis, caused by other organisms present in the 

 milk or on account of a puncture of the intestinal wall in the 

 inoculation process. The animals which survive should be 

 chloroformed in sixty or seventy-five days, and a careful post- 

 mortem examination made. The point of inoculation should 

 be examined, as well as the liver, spleen, kidneys, peritoneum 

 and membranes of the abdominal cavity, and the lymph glands, 

 especially of the inguinal region. The condition of the lungs 

 should also be noted. If lesions are found, the results must 

 be controlled by a microscopical examination of the tissue in 

 smear preparations, and in suspicious cases by a second inocu- 

 lation of animals with a suspension of the suspected tissues 

 of the first macerated in a mortar with sterile water. The 



