CHAPTER XXXVIII 



PERIODICITY IN MALARIA 



By 



Lucy Graves Taliaferro 

 The University of Chicago 



Various methods may be used to study the periodicity of the 

 asexual cycle of malarial parasites. A very accurate method in- 

 volves a statistical consideration of the changes in size of the 

 parasites such as has been recently used in the malarial parasite of 

 birds (L. G. Taliaferro, 1925). This method does not differ in 

 principle from a simple inspection of the slides, but it eliminates to 

 a large degree the unconscious selection of forms and gives a 

 numerical basis for comparisons of the average size at different 

 times. Another valid method involves ascertaining the ratio of 

 sporulating individuals to the total parasite population which has 

 also recently been used in a study of the avian parasite (Boyd, 

 1929). Where parasites are scarce, the first method will probably 

 prove more serviceable ; where parasites are numerous, the second 

 method will probably be simpler. 



If either of these methods could be applied to the human 

 malarial forms, they might elucidate some of the moot questions. 

 Inasmuch as both methods depend upon the occurrence of all of 

 the stages in the peripheral blood, Plasmodium falciparum could 

 not be as readily studied because the young merozoites leave the 

 peripheral circulation early in their development to complete it in 

 the internal organisms. Nevertheless, a number of interesting facts 

 might be obtained by modifying the first method and studying the 

 growth of the parasites when they did occur in the blood, together 

 with the time of their appearance and changes in number. More- 

 over, cultural forms might be studied, although whether or not 

 they would be comparable to the in vivo developmental forms is 

 not known. For example, Perekropoft* (1914) studied P. falci- 



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