32 REPORT ON THE DISEASES OF SILKWORMS IN INDIA 



in Experiment 7, lots 1 and 2, the result being that 100 per- cent. 

 disease was acquired in one case and 40 per cent, in the other. It 

 seemed to me, however, that perhaps the more normal source of 

 infection would be diseased moths' progeny, and two experiments 

 were tried to see what amount of infection would be picked up in 

 this way (Experiment 7, lots 3 and 4). First and second generation 

 diseased moths' progenies were mixed at hatching with disease-free 

 worms. On examining the moths from these rearings in the first 

 experiment — where 2nd generation diseased moths' progeny was 

 used — the mixed lot gave 31 3 per cent, disease while the control of 

 the diseased laying gave 16 per cent., showing that probably a fair 

 amount of infection had been picked up. In the second experiment 

 the mixed lot gave 11 3 per cent, while the control of the diseased 

 laying gave 10 per cent., showing that relatively very little infection 

 had been picked up by the healthy worms. These two experi- 

 ments are obviously imperfect as in examination it was impossible 

 to distinguish which were diseased moths' progeny and which 

 were from disease-free layings. This could only have been done 

 by the caterpillars spinning different colours or shapes of cocoon, 

 and at the time none was available. However it seems clear 

 that infection can be got from diseased moths' progeny but not 

 to a very great extent in a very small rearing. Reference may be 

 again made to the experiments in rearers' houses (Appendix IA, 

 lots 12 and 15) where diseased moths' progeny seem to have acted 

 as a source from which disease-free moths' progeny got infected. 



There are other sources of infection such as air-borne spores and 

 the clothes and hands of people coming from houses where highly 

 diseased rearings are found. The former is certainly an unimpor- 

 tant source, and the second is well guarded against in this country 

 as rearers object strongly to outsiders coming in and looking at 

 their worms, especially when disease is about. Indeed so deep 

 rooted is this feeling that it points to a past experience of highly 

 contagious diseases extending back for a very considerable time. 



How long does infesfcion last ? A large series of experi- 

 ments on the length of life of pebrine spores is recorded by Hutchin- 

 son (1920). The results are rather irregular and the conditions under 

 which the spores were kept not normal — the material being kept 

 either continually moist or continually dry — so that they cannot 

 altogether be accepted as showing what might happen under ordi- 

 nary conditions. On the whole they seem to show that when spores 

 are kept dry they retain their vitality longer than when they are 

 kept moist, and that spores kept in a dessicator may remain infec- 

 tive for 5 \ months. As, however, the atmosphere of the majority 

 of the silk-rearing centres in India is not so totally free from moisture 



