REPORT ON THE DISEASES OF SILKWORMS IN INDIA 49 



and other Indian rivers are not ideal silk-rearing districts, and the 

 climate there would seem to make the worms more liable to suffer 

 from disease. It is alsb certain that worms reared in the hills at an 

 altitude of about 4,500 feet or somewhat higher do very well. They 

 are not free from disease but they usually spin good cocoons and 

 seem generally healthy. The point to be decided is, does this im- 

 provement got by rearing in the hills persist after the worms are 

 taken to the plains — is it something that is inherited 1 Personally 

 I very much doubt it, and it is a question that cannot rapidly be 

 decided — several years of careful experimenting would be required 

 to determine whether or no there is anything in hill amelioration. 



Hutchinson (1920) gives a set of experiments which he says 

 opens up "a hopeful line of enquiry" with regard to "increased 

 .resistance to infection caused by hill rearing," but I confess I 

 cannot see on what grounds he bases his optimism. There are 

 five experiments in the set. In one there is practically no differ- 

 ence between the hill reared and the Pusa reared worms — 94 per 

 cent, diseased as opposed to 100 per cent. In another the hill 

 worms were fed on material 7 weeks and 5 days old while the 

 plains worms were fed on material 4 weeks and 3 days old — such a 

 -difference in age of infective material as would easily explain one 

 lot showing no disease while the other lot showed 30 per cent, 

 ■disease. A third lot gave 40 per cent, disease in hill reared worms 

 and 74 per cent, in Pusa reared stock, but if one examines the 

 whole series o c experiments given one finds that in the set on " the 

 effect of artificial infection a day before spinning ", from which 

 the 74 per cent, case seems to be taken, there is a case which gave 

 only a 385 per cent, infection in Pusa, actually less than the 40 per 

 cent, got in ShiUong. A fourth experiment in infected cages gave 

 35 per cent, infection in the hill reared lot while the Pusa reared ones 

 gave a 44 per cent, infection — a comparatively slight difference 

 which is well within the limits that are to be expected from the 

 chances for and against worms picking up' infection in an infected 

 •cage. In a fifth experiment the hill reared worms gave 59 per cent. 

 infection on being fed four mea's of infective material after 4th 

 moult while plains reared ones gave 100 per cent., but if all 

 Hutchinson's experiments are reviewed it will be found that 

 under the heading " the effect of artificial infection after the 

 fourth moult," from which these experiments are taken, some 

 lots of plains worms gave no infection, others 10 per cent, and 

 37 "5 per cent. — again less than the hill reared worms. For my 

 part I can see no support in these experiments for the belief that 

 hill rearing increases resistance to disease. 



I find, indeed, in the literature expressions of opinion which are 

 opposed to hill reared seed being used in the plains. Pasteur 



