84 THE FLEA [CH. 



that disease. Plague is an infectious fever caused by 

 a specific bacterial organism. Bacillus pestis was 

 first identified in 1894 by Kitasato, a Japanese, and 

 immediately afterwards, but independently, by Yersin. 

 It is an exceedingly minute, short, moderately thick, 

 oval bacillus, with rounded ends. It has the most 

 astounding power of rapid multiplication. Nothing 

 is, at present, known of its natural history outside 

 the body of the sufferer, but it can be cultivated. 

 Little is known of its toxic action, but a weak toxin 

 has been got from cultures. The bacillus itself is 

 not of a resistant nature and is easily killed by 

 heat and ordinary germicides. Acids appear to be 

 fatal to it. 



In ordinary cases the bacillus is found in buboes. 

 A bubo is nothing more than an inflamed gland. In 

 so-called septicsemic cases it is found in the blood of 

 the animal afflicted by the disease. In pneumonic 

 cases the bacillus may be found in the sputum of the 

 patient. It is the custom to speak of (a) bubonic 

 plague, (b) septicsemic plague, (c) pneumonic plague, 

 as though they were three diseases. This is in- 

 accurate: for they are only forms, with varying 

 symptoms, of one and the same disease caused by the 

 same bacillus. 



The disease which we call plague is, in truth, 

 really a fight between the afflicted animal and the 

 invading bacillus. It may be inferred from the fact 



