38 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



the waste products of the caterpillar's body are not efficiently 

 removed, and the animal becomes sluggish and its growth is still 

 further interfered with. The silk-gland (Plate II, fig. 1) may be so 

 injured that the silk-secreting cells do not produce silk in any 

 quantity and no cocoon or a very flimsy cocoon will result. In this 

 way can be explained some of the most typical symptoms of the 

 disease. 



We may take it then that the caterpillar has not to cope with any 

 very poisonous toxins produced by Nosema, but there remains the 

 fact of the very serious mechanical injury and gradual starvation 

 which the worm has to undergo. Does the caterpillar have any 

 means of resisting this ? In the first instance the infection of the 

 caterpillar seems to be relatively easily effected. That is to say, the 

 spores of Nosema bombycis, if ingested by the worm, " hatch-out" 

 in the gut and the planonts readily penetrate the gut-wall. So 

 far from preventing infection the digestive juice of the caterpillar 

 actually is the stimulus which causes the spores to dehisce. It has 

 been suggested that some disturbance of the gut, such as increased 

 acidity, may be necessary before spores can dehisce, but I cannot 

 find any proof of this. A normal caterpillar has a very alkaline 

 gut — tested by Clark and Lub's indicators it gives deep blue with 

 thymol blue (pH=9'8) — Jameson and Atkins (1921). If a cater- 

 pillar from a batch with this highly alkaline, or normal, gut be fed 

 with spores/ the spores will dehisce and the caterpillar will become 

 infected with pebrine. Further, exactly the same degree of alkalinity 

 is got (pH=9 - 8) in a heavily pebrinised caterpillar, whose gut is full 

 of spores and in which, be it remembered, auto-infection is going on, 

 that is to say, spores are dehiscing and planonts entering the gut- 

 wall. The normal gut is perfectly fitted for receiving infection, and 

 there is obviously no question of the planont being in any way 

 digested or otherwise injured by the digestive juices of the cater- 

 pillar. 



It may then be asked if all pebrine spores swallowed by a worm 

 will dehisce and set free the enclosed planonts to start multiplying 

 in the gut-wall. If a series of caterpillars be fed an emulsion of 

 spores and killed at various intervals of time afterwards from about 

 10 minutes after feeding to say 8 hours,- it will be found that all the 

 spores ingested do not dehisce— indeed in many cases the majority 

 seem to pass through the gut unaffected in any way. This is of 

 course due to the fact that the digestive juice of the caterpillar 

 stimulates only " ripe " spores to dehisce. Eipeness is doubtless 

 closely bound up with certain nuclear phenomena and as such cannot 

 be gone into here, but it will be readily understood that in the 

 development of the spore there comes a point when it is ready to 



