PERIODICITY IN MALARIA 399 



parmn in cultures at 41° C. for five generations and concluded 

 that the cycle was probably of twenty-seven hours' duration. 



Each of the methods, with its various applications, will be con- 

 sidered separately. 



The procedure in the first method, which has been fully de- 

 scribed in a previous paper (L. G. Taliaferro, 1925), consists in 

 obtaining the mean size of representative samples of asexual forms 

 at frequent intervals through as much of an infection as is pos- 

 sible and may be outlined briefly as follows : 



1. Thin ^ blood smears are made every two or four hours 

 through the day and night over at least several days or longer if 

 possible. These are stained with Wright's stain. 



2. From slides from each time-interval 50 or 100 outHne draw- 

 ings of the asexual forms - as they are found at random are made 

 at a standard magnification by means of a camera lucida. (X3000 

 seemed a convenient drawing magnification.) 



3. The drawings from each set are measured by obtaining the 

 product of the average length by average width in some convenient 

 standard. (Microns may be used.) ^ 



4. The mean -^^ of each set is obtained by dividing the sum 



n 



of the measurements {^x) by the number of individuals drawn 

 {n). 



When these data are plotted graphically against the time of an 

 infection, they will give, where there is a periodicity, a curve some- 

 what like that shown in Fig. 26 (curve of the mean size). 



Such a curve, since it is based on averages, does not indicate the 

 degree of synchronicity of the cycle. This may be ascertained by 

 making frequent slides during the time of sporulation and finding 

 the percentage of young forms. If synchronicity were absolute, at 

 a given instant, the percentage of young forms would increase 

 from o to 100%. If, on the other hand, there were no syn- 

 chronicity, the percentage of young forms would remain constant 

 throughout the infection. Such a procedure will also disclose 



* Thick smears might also be adapted for use which would enable the 

 study of lighter infections. 



^ It was found best during the course of the work to omit the gametocytes 

 as they mask, to some extent, the changes in mean size of the asexual forms. 



^ This measure of "size" is neither a measure of volume nor cross section, 

 but is easy to obtain and sufficiently accurate. 



