294 



Determination of the Periodicity of 

 Parasite Development 



The inspection of a temperature chart is not in 

 itself sufficient to determine the cycle of develop- 

 ment of a parasite. Thus, as is well knoAvn, a 

 quotidian temperature chart may be produced by 

 a double tertian (simple) or by a triple quartan 

 infection. If then, in the case of the double 

 tertian, we made microscopical examinations at 

 definite intervals for forty-eight hours, we should 

 find in the blood at any particular time parasites 

 in two phases of development corresponding to 

 each cycle. The accompanying chart shews how, 

 in the case of what proved to be the malignant 

 tertian parasite, we were able to establish the 

 cycle of development. We proceeded to make blood 

 examinations at frequent intervals (four hours). 

 We found that at any particular time parasites 

 of various sizes might be found, but by counting 

 several hundred parasites in each film and. esti- 

 mating their size with a micrometer we found 

 that at any particular time there was a prepon- 

 derance of parasites of one size. Thus, at ten 

 p.m. on the 2nd, there are numerous small forms, 

 i.e., about one-seventh to one-eighth of a red cell 

 in diameter, and it is not till ten p.m. (about) on 

 the 4th that the same condition of blood is found 

 again, accordingly the parasite had a develop- 

 mental cycle of forty-eight hours (approximately). 

 And, further, we determined the periods taken to 

 develop from small forms to largest forms in the 

 peripheral blood (about eighteen hours) and the 

 disappearance of these and the reappearance of 

 numerous youngest parasites (about thirty hours). 



