December, '13] glaser and chapman: gipsy moth wilt disease 483 



European investigators have advanced various theories concerning 

 the exciting cause of the polyhedral diseases. At one time bacteria 

 were thought to be responsible, especially by Hofmann and Tubeuf. 

 The polyhedral bodies were regarded as being formed by the tissue 

 cells as a reaction against the bacterial toxins. In 1911 Escherich 

 and Miyajima expressed the opinion that we must look upon the poly- 

 hedral bodies as the carriers of the virus. Bolle at one time believed 

 a certain Microsporidian (Microsporidium homhycis) to be responsible 

 for the disease. According to Prowazek's latest paper in 1912, on 

 the "Gelbsucht" of the silkworm, Knoch delivered a lecture in Stutt- 

 gart on the 14th of March, 1912, in which he said that little refractive 

 granules appear in the blood corpuscles. These multiply and infect 

 the nuclei of tissue cells where their amoeboid membrane hardens and 

 they change into polyhedral bodies. He further said that the minute 

 granules which resemble the Chlamydozoa of Prowazek are the vegeta- 

 tive; the polyhedral bodies the resting stages of the causative organ- 

 ism. 



Prowazek, in the paper above mentioned, infected some fifteen or 

 sixteen caterpillars with emulsified diseased material which he passed 

 with difficulty through the Berkefeld and through his Agar-Ultra 

 filter. The filtrate contained no polyhedral bodies and no bacteria, 

 as control cultures showed. The caterpillars died typicall}^ and so 

 he concluded that in some cases healthy caterpillars could be infected 

 with material free from polyhedra. These experiments are suggestive, 

 but cannot be taken seriousl}^ because no controls were used and be- 

 cause the blood test was the only precaution taken in diagnosing the 

 health of caterpillars. 

 The Exciting Cause of the Wilt Disease a Filterable Virus 



Thirty filterable viruses are now known to be responsible for certain 

 infectious diseases in man and the lower mamm^als, but to our knowl- 

 edge only one has been described in insects, namely that of Sacbrood, 

 a bee disease discovered by White in 1913. 



In our infection experiments last year, we obtained negative results 

 with the material passed through the Berkefeld filter. This was due 

 to the fact that the material was so concentrated that a slimy film was 

 deposited on the outside of the candle and withheld the virus. A 

 concentrated emulsion of diseased material is so full of polyhedral 

 bodies, cellular debris, hairs and pigment granules that it very soon 

 plugs up the pores of the filters. This year caterpillars, which died 

 typically of the disease, were crushed with just enough sterile water 

 to facilitate the crushing. This material was then strained through 

 cheese cloth and filtered by m.eans of suction through filter paper. 

 The filtrate was diluted in one case with fifty, in another with twenty- 



