n6 



ST"UDY AND IDENTIFICATION OF BACTERIA 



of a culture, we consider the possibility of contamination. Litmus milk is rendered 

 slightly acid but not sufficiently to change the lilac color. Glucose broth is made 

 slightly acid but there is no effect on lactose. 



Blood cultures in septicsemic plague may show from 5 to 500,000 bacilli per c.c. 

 Smears from the blood in such cases are positive in only about 17%. 



The plague bacillus grows well at room temperature its optimum 

 temperature being 30 instead of 37C., as is usual with pathogens. 

 Next to the salt agar culture, the most characteristic one is the stalac- 

 tite growth in bouillon containing oil drops on its surface. The culture 

 grows downward from the undersurface of the oil drops as a powdery 



FIG. 32. Pest bacilli from spleen of a rat. (Kolle and Wassermann.) 



thread. These are very fragile, and as the slightest jar breaks them, 

 it is difficult to obtain this cultural characteristic. 



While Klein states that B. coli, Proteus vulgaris and, in particular, B. bristolensis 

 may be mistaken for plague bacilli, if bipolar staining alone be relied upon, yet it is 

 B. pseudotuberculosis rodentium which may confuse an experienced worker. While 

 this latter is only moderately pathogenic for rats yet the fact that rats may be 

 immunized to B. pestis by inoculation with B. pseudotuberculosis rodentium brings 

 up the suspicion of identity of the two organisms. In diagnosing ^always use animal 

 experimentation. Owing to the difficulty in emulsifying plague bacilli, agglutination 

 tests are not satisfactory. B. tularense resembles B. pestis. See Part IV. 



Albrecht and Ghon have shown that by smearing material upon the 

 intact, shaven skin of a guinea-pig, infection occurs. This is the crucial 

 test. 



A pocket made by cutting the skin of a guinea-pig with scissors and extended 

 subcutaneously with scissors or forceps, into which a piece of the suspected plague 



