February, '16] chapmax and glaser: wilt of gipsy moth 151 



24. The incubation period of wilt varies, and temperature at times 

 seems to bear an important relation to this variation. 



25. A large number of caterpillars used in the experiments died of 

 disturbances in their normal physiological activities. 



26. The success of wilt infection experiments is absolutely depend- 

 ent upon attention to seemingly insignificant details. 



27. Genetic immunity of certain individuals is probable. 



28. Active immunization with sublethal doses is possible. 



29. The polyhedral bodies may be stages of the filterable virus, but 

 as yet no evidence to substantiate this view has been produced. 



30. Infection naturally takes place through the mouth by means of 

 the food. 



31. There is no e\adence that the wind is an important factor in 

 distributing the disease. 



32. Some of the imported parasites may be important factors in 

 aiding the dispersion of wilt. 



33. Although probable, there is no definite e\'idence as yet that wilt 

 is transmitted from one generation to another. 



Problems Requiring Further Investigation 

 From a review of our work during 1913 it seemed apparent that many 

 wilt problems needed further investigation and verification. For 

 this reason we concentrated our work upon the following questions: 



(a) Can we obtain further evidence in order to substantiate our 

 view that wilt is a true infectious disease? 



(b) Can we produce further e\ndence that wilt is caused by a minute 

 filterable organism? 



(c) If wilt is caused by a filterable virus can we obtain some idea 

 of its size? 



(d) Has wilt a definite period elapsing between inoculation and 

 death? 



(e) What influemce do chmatic conditions (temperature and humid- 

 ity) have on the length of this period? 



(f) Does immunity towards wilt exist in certain members of the 

 gipsy moth race? 



(g) Is wilt transmitted from one generation to the next through 

 the egg? 



Difficulties Encountered in 1914 

 In order more lucidly to illustrate the satisfactory methods devised 

 during the summer of 1915 we would like to present five out of fifteen 

 experiments performed during the summer of 1914. The gipsy moth 

 caterpillars used for these experiments were collected in the field 

 while in the third and fourth instars from localities where no wilt had 

 been noticed up to the time of the collection. The animals were 



