402 . RESEARCH IN PROTOZOOLOGY 



work), the cycle was twenty-four hours* throughout the acute, 

 crisis, chronic and relapse periods, in fact whenever parasites could 

 be found in the blood. These facts are illustrated graphically in Fig. 

 26 which shows the changes in mean size of the asexual forms 

 encountered in Bird 61 through a part of the acute and chronic 

 period. The synchronicity of the strain is shown by the coefficient 

 of variation curve (Fig. 26) which is fairly constant and low 

 during the major portion of the cycle (varied roughly between 

 fifteen and thirty-five per cent) but rises and falls precipitously 

 at each sporulation-time (100-135 per cent). The duration of 

 sporulation is shown in Fig. 27 where the percentage of small 

 forms and the coefficient of variation are plotted from data at 

 hourly periods during one period of sporulation and indicate that 

 whereas most of the parasites sporulate between 6:30 and 9:30 

 p.M.^ there are a few stragglers before and afterward. The cycle 

 in this strain is, therefore, fairly synchronous. Roughly, at 10 :oo 

 P.M., all of the asexual forms are small in size, they then grow in 

 size until by 2 :oo p.m. the next day they are all large, and at 6:00 

 P.M., large and small forms, representing sporulation, both occur 

 (Fig. 28). As has been previously pointed out, where the cycle is 

 simple and growth of the forms is nearly synchronous, these 

 changes can be roughly gauged by inspection of the slides, but 

 where there is any marked lack of synchronicity, the observer is 

 liable unconsciously to be biased in his selection of forms. 



In another strain of avian malaria, isolated by Whitmore and 

 which Hartman (1927/?) has identified as P. prcecox (Grassi and 

 Feletti, 1890), the author found a thirty-hour cycle. This strain 

 is not as synchronous as the one just described; the coefficient of 

 variation curve is higher during the non-sporulating periods 

 (varied roughly between forty and seventy per cent) and did not 

 rise as precipitously nor as high (81-104%) during the sporu- 

 lation periods. The cycle, moreover, is not as clear cut and the 

 following facts make it desirable that the work be repeated : 

 The sexual as well as the asexual forms were included in the 

 mean size curve, whereas it would probably be preferable to omit 



* After a three months' study of the cycle I concluded that it was twenty- 

 four hours and one minute, but with longer studies, Hartman (1927a) and 

 I (1928) have found it to be exactly twenty-four hours. The occurrence of 

 the cycle has been corroborated by Drensky and Hegner (1926) and Boyd 

 (1929). 



