February, '16] CHAPMAN AND GLASER: WILT OF GIPSY MOTH 157 



checks and none in the stock. In Table XI one case of wilt is recorded 

 in the checks and none in the stock. The explanation offered to ac- 

 count for the 4 per cent check mortality is based on the above data, 

 namely, when the stock wilt mortality is low or zero, the checks which 

 are derived from such stock are likely to be healthy; when the stock 

 wilt mortality is high, some of the checks which are derived from such 

 stock are likely to be diseased. Table XI seems to be a sHght excep- 

 tion to this rule. In this experiment no wilt is recorded in the stock, 

 ])ut one in the checks. It must be borne in mind, however, that the 

 number of this stock culture was rather small and it is really unfair 

 to base a health estimate on it. Of course, this one check may not 

 have been chronically infected before being used. It may have con- 

 tracted the disease subsequently by accidental infection, but this 

 seems unlikeh'. 



Under the heading died of "other causes" are grouped all of those 

 animals that showed none of the gross and microscopic symptoms of 

 wilt. Caterpillars which succumbed to this "other cause" death were 

 usually in the fourth or fifth stage. They frequently hung by their 

 prolegs in the typical wilt fashion, but their skin was tough and did 

 not rupture easily as is the case with typical wilted individuals. On 

 dissection such individuals proved to be practically free from body 

 fluids, in contradistinction to the deliquescent state of wilted animals. 

 In many cases the organs and tissues were almost shrunken beyond 

 recognition due to the loss of blood and body fluids. No polyhedra 

 were ever found in such animals, but smears from the intestine revealed 

 countless Saccromv^cetes and Micrococci. Sections through these 

 caterpillars failed to reveal the above mentioned microorganisms in 

 any organ excepting the intestine. The Saccromycete and a Micro- 

 coccus were isolated from animals which died of this disease and other 

 healthy ones were infected with these pure cultures. We failed to 

 reproduce the disease with either microorganism. It might be well to 

 mention that the Saccromycete grows very readily on bean and potato 

 agar, and the Micrococcus flourishes on beef infusion and on beef 

 extract agar. 



A very interesting fact was noticed in all of the stock cultures and 

 experimental animals. Nearly all of the individuals which died of the 

 "other cause" death and which revealed the Saccromycete and Micro- 

 cocci microscopically and culturalh', were derived from the foreign 

 eggs given us by Professor Goldschmidt. Very few American cater- 

 pillars could 1)e found which yielded the above named microorganisms. 

 The few found probably became infected from the foreign stock. By 

 comparing the tables representing American with those representing 

 foreign animals, and further by comparing the percentage of "other 



