480 



BACILLI IN CHRONIC INFECTIOUS DISEASES. 



uated pipette ; in spreading these uniformly by means of a platinum 

 needle and a turn table ; in covering the dried film with a film of 

 blood serum, and coagulating this by heat ; and, finally, in staining 

 and counting the bacilli in a series of slides from the same specimen, 

 and from the average number found in a single drop estimating the 

 total number in the sputum for twenty -four hours. 



Pathogenesis. Man, cattle, and monkeys are most subject to 

 contract the disease naturally, and it may be communicated by in- 

 oculation to many of the lower animals guinea-pigs, field mice, rab- 



FIG. 119. Limited epithelioid celled tubercle of the iris. X 950. (Bautn^arten > 



bits, and cats are among the most susceptible animals ; and in larger 

 doses dogs, rats, white mice, and fowls may also be infected. 



When tuberculous sputum is introduced beneath the skin of a 

 guinea-pig the nearest lymphatic glands are found to be swollen at 

 the end of two or three weeks, at the same time there is a thickening 

 of the tissues about the point of inoculation ; later a dry crust forms 

 over the local tuberculous tumefaction, and beneath this is a flattened 

 ulcer covered with cheesy material. The animals become emaciated 

 and show difficulty in breathing, and usually succumb to general 

 tuberculosis, especially involving the lungs, within four to eight 

 weeks. Injections of tuberculous sputum, or of pure cultures of the 

 bacillus, into the peritoneal cavity give rise to extensive tuberculo- 

 sis of the liver, spleen, and lungs, and to death, as a rule, within 

 three or four weeks. Rabbits are less susceptible to subcutaneous 



