566 



Dr. H. L. Duke. 



[Sept. 2, 



both species the disease is typically a very rapid one in white rats, and the 

 number of trypanosomes in the peripheral blood shortly before death is 

 enormous. The course of the disease in dogs in the above table is not 

 characteristic of either T. brucei or T. evansi, which are rapidly fatal to these 



Length in Microns. 



animals. In the case of surra, however, the disease appears less rapid in its 

 course than with nagana. Thus Laveran quotes experiments of Lingard's in 

 which dogs lived 27£, 29, 34, 36, 47, 97 days after inoculation with T. evansi, 

 the last having been inoculated from a naturally infected bovine. In the case 

 of T. brucei, however, the same authority gives 26 days as the maximum 

 duration of nagana in dogs. 



Though by no means a typical T. evansi it is plain that the above 

 experiments suggest this trypanosome rather than T. brucei, and this con- 

 clusion is supported by the evidence of morphology. 



I shall take this opportunity to consider briefly the question of the 

 biometric method of diagnosing trypanosomes from the point of view of a 

 worker dealing with the problem in the field. Of late a great deal of attention 

 has been devoted to this method, with the result that there appears to be 

 some danger of its attaining undue importance. In certain cases it is of 

 undoubted value, as in discriminating between two such species as T. vivax 

 and T. uniforme, where the difference in size is one of the most important 



