II. THE GENERATION OF VIRUSES 



147 



viruses not upon the generation of viruses themselves. However, as 

 will be mentioned later, there are many good reasons to assume that 

 effect is involved rather in the virus generation or in the provirus 

 activation than in the alteration of the host resistance. 



The writer made an investigation into the seasonal effect upon the 

 incidence of measles, and obtained interesting data. The investigation 

 was carried out with pupils of Japanese primary schools in Shanghai, 

 when the writer was a member of the Shanghai Science Institute 

 (46). 



The seasonal effect upon the occurrence of the disease was found 

 to be very striking as shown in Fig. 18. However, the curve shown 



1 2 3 4 5 6 7 8 9 10 11 12 1 2 

 Months of infection 



Fig. 18. The seasonal change in the incidence of measles in Shanghai. 



in this figure representing the relation between the morbility and 

 season is distinctly different from those obtained by other investigators 

 at different districts as indicated in Fig. 19, in which it is also shown 

 that the season effect varies considerably from district to district. In 

 Shanghai and Cleveland the epidemic occurs only once in a year, in 

 late spring or in early summer, while in other districts, especially in 

 Wien and Liibeck, in addition to this peak, the second epidemic is 

 seen in late autumn or in early winter, although in Shanghai there 

 is some indication of this second peak. 



On the other hand, it is of very interest that the seasonal change 

 of impregnation of Japanese women bears a striking resemblance to 

 that of the morbility as indicated in Fig. 20. The impregnation 

 months cited in the figure are calculated by substracting 3 from, birth 



