February, '16] CHAPMAN AND GLASER: WILT OF GIPSY MOTH 161 



Period from Infection to Death 



In wilt a definite period elapses between the time of inoculation by 

 feeding and death. This period varies slightly depending on the dosage, 

 but is fairiy constant in a certain class of experiments in which the 

 dosages are constant. Tables XIX and XX graphically illustrate what 

 happened in our simple and Berkefeld infection experiments. Table 

 XIX represents the simple infections. Each square along the ordinate 

 represents the greatest number of caterpillars that died on a particular 

 day; the abscissa represents the number of days covered by the experi- 

 ments. The first deaths occurred 13 days and the last deaths 27 days 

 after inoculation. The highest point in the mortality is reached 18 

 days after inoculation. The mean for the entire simple infection 

 experiments is 20 days. Table XX represents the Berkefeld infections. 

 In this series the first death occurred 15 days and the last 29 days after 

 inoculation. The highest point in the mortality is reached 23 days 

 after inoculation. The mean for the entire Berkefeld infection experi- 

 ments is 23 days. 



By comparing the simple infection Table (XIX) with the Berkefeld 

 infection Table (XX), it will be seen that in general the time from 

 inoculation to death in the Berkefeld experiments is longer than in 

 the case of simple infections. This difference between the two sets 

 of experiments is due to differences in the concentration of the doses 

 of the virus administered. In the Berkefeld experiments, as previously 

 mentioned (p. 153), dilution, absorption, and film deposition play im- 

 portant r61es in decreasing the concentration of the virus and hence one 

 would expect a longer period to elapse before the disease proves fatal. 

 Table XXI represents Tables XIX and XX combined. The mean for 

 both sets of experiments is 21 days. 



Daily humidity and temperature records were kept during the entire 

 experimental season by means of self-recording instruments for the 

 purpose of determining whether or not these climatic factors had any 

 influence in shortening or lengthening the period from inoculation to 

 death. We have very carefully compared all of our records with the 

 wilt mortality occurring in our experiments, but we have been abso- 

 lutely unable to find any correlation between temperature and wilt or 

 humidity and wilt or between both climatic factors and wilt. 



On the basis of this failure to find any correlation (1915) between 

 climatic conditions and wilt in our insectary, we would not like to 

 exclude such a possible influence. Our records for the entire season 

 show that the temperature and humidity were fairly constant. No 

 extremes were reached in our insectary which was a subterranean 

 greenhouse, so we feel obliged to continue these climatic observations 

 in connection with wilt for another season or two before making any 

 final statement. 



