Dccember,'13] GLASER AND CHAPMAX: GIPSY MOTH WILT DISEASE 485 



he found, a sign of some metabolic disturbance. Quite a few larvae 

 were killed by the imported tachinid parasite, Compsilura concinnata, 

 and the rest transformed into moths. The only way we can account 

 for these moths is on the supposition that they arose from immune 

 caterpillars or from such as had escaped infection in some way. A 

 greater number of caterpillars (48 out of 85) died in the experiments 

 with unfiltered virus. This seems to show that the organism is filter- 

 able but with difficulty. The filter became clogged up after a short 

 time and, therefore, only a certain amount of the virus could pass 

 through it and, in order to overcome this difficulty in part, the old 

 filters were replaced by new ones every few minutes. Among the 

 entire number of controls, 162 caterpillars, only three died of wilt. 

 This is equivalent to about 1.8 per cent, a very small percentage and 

 one which can almost be overlooked as an experimental error in such 

 a large set of controls when compared with the numbers that died in 

 the experiments. In the controls as well as in the stock trays a great 

 number of caterpillars died of the physiological cause already mentioned. 

 Especially significant are those which died of this cause in the stock 

 trays for these caterpillars w-ere not at all infected, so that it is impossi- 

 ble to attribute the death-rate in the controls to some toxic effect of 

 the sterilized virus. Laboratory conditions are poor at the best and 

 our records show that very high temperatures were probably responsi- 

 ble for this "physiological death" as w^e have called it. In the labora- 

 tory, especially during high temperatures, the food plants put into 

 tra3^s dry out rapidly, no matter how often they are renewed. Dew 

 and rain cannot wet them and very likely the lack of water, in other 

 words thirst, was responsible for the mortality. AVe did not care to 

 dampen the leaves artificially very much for fear that we might pro- 

 duce a condition still more unnatural and one that might favor the 

 development of moulds in the trays. 



The polyhedral bodies have as yet revealed nothing of a parasitic 

 nature. They may, of course, be a resting stage of a filterable vegeta- 

 tive form, but we are rather inclined to regard them as reaction bodies. 

 They are possibly products of nuclear digestion produced by the virus 

 invading the nuclei and digesting the chromatin. 



We should like briefly to consider one more matter. It is claimed 

 in this country, notably by Mr. William Reiff, that the disease is air 

 Ijorne and that caterpillars can be infected in the woods by hanging 

 out small cheese-cloth bags containing the remains of individuals that 

 have died of the disease. With this point in view we arranged a set 

 of boxes near some windows through which the wind blew steadily for 

 over ten days. The boxes were closed except on two sides, namely 

 the side facing the window and the side facing the interior of the room. 



