158 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. &■ 



cause" deaths in the stock cultures with the same deaths in the experi- 

 mental animals, actual experiments, checks and untreated individuals, 

 the facts to which we have here called attention stand out very vividly, 

 (Compare Tables VI, VIII, X and XI with Tables VII and IX.) 



Professor Goldschmidt experienced a high mortality in some of his 

 Japanese gipsy moth cultures. We had the opportunity to examine 

 many of his dead animals and found that the percentage of deaths due 

 to the "other cause" was very much greater than the percentage of 

 wilt mortality. 



So far as the ''other cause" mortality is concerned, the following 

 facts are clear: 



(1) The "other cause" mortality discussed in this article is not at 

 all comparable to the mortality similarh'^ designated by Glaser and 

 Chapman in 1913. In 1913 it was due to low humidity; in this case 

 probably due to one or more microorganisms. 



(2) We believe that this "other cause" mortalit}^ is a specific dis- 

 ease which has no direct relation to wilt. 



(3) This "other cause" mortality was never found during previous 

 seasons in our American laboratory or field animals. 



(4) It appeared for the first time this year (1915) in our foreign cul- 

 tures and later spread to two or three American cultures. 



(5) This new disease appears only during the later stages of the 

 caterpillars (fourth and fifth stages). 



By comparing Tables VI, VII, IX and X it will be seen that from 

 one to five moths were obtained in nearly all of the actual infection 

 experiments. There can be no doubt that the caterpillars partook of 

 the virus for we were very persistent in seeing that thej^ actually 

 drank. Therefore, we offer two explanations: first, that certain 

 individuals among gipsy moth caterpillars are immune to wilt. We 

 have obtained eggs from such individuals and it will be interesting to 

 note during the next season whether this immunity is transmitted to 

 any of the next generation. Second, that certain individuals after 

 inoculation become chronically diseased, but are nevertheless capable 

 of undergoing metamorphosis. If this is the case wilt might be trans- 

 mitted from one generation to another through the egg. The rearing 

 of individuals from such eggs ought to throw much light on the subject. 



Berkefeld Filtrate Experiments 

 Glaser and Chapman (1913) showed that bacteria in the ordinary 

 sense of the word are not etiologically related to wilt, but that the 

 evidence is very great in favor of the view that wilt is caused by a 

 filterable virus. 



