234 



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 estimating their size with a 

 micrometer we found that at any particular time 

 there was a preponderance 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 developmental 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). So that by determining these 

 three periods we were able to conclude that the 

 parasite was the malignant tertian. 



In order then to determine the cycle of a parasite 

 it is necessary : 



1. To estimate the size and percentage of 

 parasites of each size at any particular time, e.g., 

 starting with the onset of the attack. 



2. To follow each group to its period of maxi- 

 mum development in the circulation. 



3. To estimate the time between this period and 

 the next appearance of young forms. 



4. To estimate the time between the appearance 



