February, '16] CHAPMAN AXD GLASER: WILT OF GIPSY MOTH 159 



The following experiments are offered as further proof for our view. 

 Tables XII and XIII represent two experiments which duplicate one 

 another in every detail. 



Wilted material was ground up with sterile water and strained 

 through cheesecloth. The liquid was then filtered through paper and 

 equalled 70 c.c. This was next filtered through a Berkefeld "N" 

 candle by gravity. Platings were made of the filtrate and since no 

 bacteria grew it was considered sterile for ordinary forms. A portion 

 of this same filtrate was centrifuged electrically and the bottom sedi- 

 ment examined microscopically. No bacteria or polyhedral bodies 

 could be detected in fresh and stained smears. The animals used for 

 these two experiments were all in the fourth stage and came from an 

 American stock. They were, furthermore, all derived from the same 

 egg cluster. Thirty-two animals were fed, by means of an eye dropper, 

 with the Berkefeld "N" filtrate; 28 with the filtrate sterihzed by auto- 

 claving and 20 untreated individuals accompanied this series. In one 

 experiment, Table XII, nine out of 32 animals infected with the 

 unsterilized virus died of wilt. Moths were obtained from all the rest. 

 In the other experiment, Table XIII, four out of 32 animals infected 

 with the unsterilized virus died of wilt. The remaining individuals all 

 transformed. Table XIV represents another similar experiment with 

 slight variations. Fifth stage American caterpillars were used. The 

 wilted material after preparation equalled 25 c.c. This was diluted to 

 100 c.c. and filtered through a Berkefeld "N" candle by means of a 

 vacuum of about 27 inches. Ten animals were fed with the filtrate and 

 ten with the filtrate sterilized by autoclaving. Four out of the 10 

 animals infected with the unsterilized virus died of wilt; three in the 

 experiment and two in the checks died of "another cause" and moths 

 were obtained from the remainder. Of course, no death was diagnosed 

 as wilt unless all the gross and microscopic symptoms were typical. 



By comparing the Berkefeld experiments with the simple infection 

 experiments, one is at once impressed with the small number of deaths 

 among the infected animals (23 per cent) in the former against 68 

 per cent in the latter. Of course, immunity may account for a number 

 of the moths, but the difference between the two sets of experiments is 

 too great for the immunity theory to account for all. This difference 

 between Berkefeld and simple infection experiments was also noticed 

 in 1913, and in 1914, and we offer the explanation presented on page 

 153 (absorption by candle and film deposition). Significant in these 

 Berkefeld experiments is the fact that none of the checks died of wilt. 

 As can be seen from the tables (XII, XIII and XIV), the condition 

 of the stock was responsible for these gratifying results. 



