PLAGUE 83 



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 dew drop-like colonies are really bac- 

 terial 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. 



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 



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



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. 



In diagnosing always use animal experimentation. Albrecht and 

 Ghon have shown that by smearing material into the intact, shaven 

 skin of a guinea-pig, infection occurs. This is the most crucial test. 

 Mice inoculated at the root of the .tail quickly succumb. Rats, this 

 being a primary disease of rats, are of course susceptible. In natural 

 plague of rats, the lesions, which establish a diagnosis even without the 

 aid of a microscope, are subcutaneous injection of the flaps of the 



