30 REPORT ON "THE DISEASES OF SILKWORMS IN INDIA 



were put into the house on hatching and reared to maturity, the 

 resulting moths then being examined for disease. Every day the 

 floor, which was very dusty, was swept around with a brush so that 

 the dust was raised in the air and might fall on the worms. The 

 stand on which the worms were, was covered with dust. In short the 

 conditions were extremely dirty and the dust was extraordinarily full 

 of spores — infinitely worse surroundings than worms could possibly 

 be subj ected to in the poorest and worst rearers' house. The experi- 

 ment was repeated five times, the house being freshly re-infected 

 each time. The results are given in Experiment 4, Appendix III. 

 As a rule the percentage of moths infected in the house was about 

 10 or 12 per cent. — that is to say, about the lowest that is got in 

 hereditary infections. On one occasion the number of infected 

 moths was high — 40 per cent. — and it is to be noted that this was 

 in the bund for the beginning of September. Even in exceptionally 

 infective surroundings, then, it may be said that usually a heavy 

 infection is not to be expected. 



In order to arrive at an estimate of the amount of infection picked 

 up by caterpillars from perfectly disease-free seed when subjected to 

 normal infective surroundings, layings of very carefully examined 

 moths were reared for me in Bengal by various rearers in their houses 

 and by their own method. Cocoons of their own rearing from their 

 own seed were also procured and examined. During the first of 

 these experiments — Appendix IA, lots 8 and 9 — the rearers had 

 no worms of their own being reared while mine were being reared, 

 and my worms, as will be seen, showed no pebrine. During the 

 second experiment they were rearing their own seed at the same time 

 and disease was got— in two cases very little and in two other 

 cases 18 and 21 per cent. (Appendix IA, lots 12-15). When 

 my seed showed about 20 per cent, disease their own showed from 

 60-90 per cent. When my seed showed little disease theirs showed 

 1-15 per cent. (Appendix IA, lots 17-20). I believe that infec- 

 tion was carried to my worms from their own diseased stock by the 

 hands and clothes of the rearers — the method of carrying infection 

 that Pasteur (1870) believed to be most important — it was not so 

 much in the house itself. Thus under ordinary village conditions 

 . if we start with good seed very little disease will be acquired. It 

 will be seen here again that hereditary infection is much more to be 

 dreaded than contaminative, although that too is of some importance 

 if diseased stock is reared alongside of healthy. 



Other sources of infection. It seemed to me that the tray 

 on which the worms were reared was probably a much more serious 

 source of infection than the house itself, and experiments were made 

 to test this idea. The series of experiments about to be noted are 



