276 KAN-ICHIRO MORISHIMA 



forms whose characteristics are easily studied and in which 

 generation follows generation with such speed that observation 

 over the period of a year or longer might correspond to ages 

 of development among the higher species. Moreover, from a 

 purely practical point of view it is necessary to know to some 

 extent just how much and how permanent a degree of variation 

 is to be expected when well-known species are subjected to alter- 

 nation between the conditions prevalent in artificial media and 

 those existing in the human and animal bodies. 



In the following studies the VvTiter has occupied himself exclu- 

 sively with the changes observed in the typhoid bacillus. 



Strains 



The cultures employed in this study were 138 in number and had been 

 carried on artificial mediums since their isolation from patients. They 

 were divided into three groups, as follows : 



1. The stock cultures of the United States Army Medical School . . 116 



2. Cultures collected by Dr. Oscar Teague 10 



3. Cultures collected by Lieut. R. C. Colwell in France, and given 



us by courtesy of Lieutenant-Colonel Nichols 12 



The sources of these cultures were as follows : 



strains 



Blood cultures 55 



Stool cultures 15 



Urine cultures 11 



Bile cultures 1 



Sources unknown 56 



Duration of cultivation on artificial media: 



Over two years 15 



One to two years 25 



Six to twelve months 42 



Less than six months 32 



Recent isolation 11 



Age unknown 13 



