408 



BACILLI IN CHRONIC INFECTIOUS DISEASES. 



then shaking it thoroughly in a bottle containing sterilized gravel 

 or pounded glass ; in carefully measuring the total quantity of fluid, 

 and in dropping upon glass slides uniform drops by means of a grad- 

 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- 



Fio. 121,-Llmited epithelioid celled tubercle of the iris, 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 

 K'liiiea-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 sh>\v ditliculty in breathing jind usually succumb to general 

 tuberculosis, especially involving the lungs, within four to eight 

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



