PLAGUE CULTURES 



97 



from three to twelve microns in length, more resembling cultures of moulds than 

 bacteria. Another point is that on the inoculated plain agar we are in doubt at 

 the end of twenty-four hours whether the dewdrop-like colonies are really bacterial 

 colonies or only condensation particles. By the second day, however, these colonies 

 have an opaque grayish appearance, so that now, instead of questioning the presence 

 of a culture, we consider the possibility of contamination. 



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

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



FIG. 31. Pest bacilli from spleen of a rat. (Kolle and Wassermann.} 



The plague bacillus grows well at room temperature -its optimum 

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

 Next to the salt agar culture, the most characteristic one is the stalactite 

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

 grows downward from the under surface of the oil drops as a powdery 

 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. 



Albrecht and Ghon have shown that by smearing material upon the 

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

 crucial test. 



