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- 
Fic. 119.—Limited epithelioid celled tubercle of theiris. x 950. (Baumgarten) 
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 
tuberctlosis, 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, asa rule, within 
three or four weeks. Rabbits are less susceptible to subcutaneous 
