484 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



five times its volume of sterile water. This was then passed through 

 a Berkefeld "Grade N" filter and used for the infection experiments. 

 The filtrate was sterile in so far as bacteria were concerned as control 

 cultures on nutrient agar, gelatine and caterpillar soup showed. Mi- 

 croscopical examination showed no polyhedral bodies. Nothing could 

 be observed even in a dark -field except some very minute dancing 

 granules also noticed by Prowazek in his experiments with silkworms 

 (p. 272). These little granules may be identical with those observed 

 in diseased tissue mentioned in the first part of this paper. This 

 matter, however, is still so indefinite that speculation seems to be 

 useless, but, since they were never found in the tissues of healthy 

 caterpillars, their presence is worth recording. 



A large number of caterpillars were fed with the Berkefeld filtrate 

 smeared on red oak leaves. In order to establish uniformity in the 

 experiments, all caterpillars of the same series were kept in one room 

 where they could be subjected to the same degree of heat and humidity. 

 Each caterpillar was kept in a sterilized pasteboard tray by itself, 

 and fed with fresh red oak leaves after the infected leaves had been 

 partially eaten. The oak leaves all came from a vicinity which was 

 not infested with caterpillars. Thus the possibility of bringing the 

 infection from the outside into the laboratory was excluded. Another 

 matter considered was the age of caterpillars used in these experiments. 

 If caterpillars are near the pupal stage, they cease feechng and are, 

 therefore, difficult to infect, so it is important to get them young enough 

 so that they will be sure to feed. 



In one series of experiments fifty caterpillars were fed with the Berke- 

 feld filtrate, in another forty, in a third twenty. The same number 

 was fed with material before it was passed through such a filter and a 

 large set of controls fed with Berkefeld filtrate which had been steril- 

 ized by autoclaving accompanied each series. 



Out of the entire lot of caterpillars (110) fed Avith the unsterilized 

 Berkefeld filtrate, twenty-eight died with typical wilt symptoms. 

 Microscopical examination showed polyhedral bodies to be present in 

 abundance and stained smears and cultures in nutrient broth showed 

 that bacteria had taken no part. Quite a few of the caterpillars died 

 of another cause which we will discuss more in detail at another time. 

 Suflace it to say that the extreme heat during July of the past summer 

 had much to do with the death of a great many of the caterpillars. 

 Their death was due to disturbances in the normal physiological 

 functions and not due to infectious disease. Caterpillars dying from 

 this cause were not very flaccid, their skin was tough; they were not 

 disintegrated, but more or less dried out. Polyhedral bodies were not 

 present, but usually a great many crystals with radiating lines could 



