REPORT ON THE DISEASES OF SILKWORMS IN INDIA 31 



to be taken as a pendant to the rearing of worms in the artificially 

 infected houses : they are extreme cases unlikely to be realized 

 under ordinary conditions. Small bamboo trays such as the rearer 

 uses were smeared with a mixture similar to that used in infecting 

 the houses, only the dust was moistened with water in order to make 

 it stick. The experiment was repeated six • times (Experiment 5, 

 Appendix III). As a rule the amount of disease picked up was 

 very great, rising as high as 100 per cent, on one occasion. The 

 lowest percentage of disease was 15"8 and the average was over 50. 

 There seems to be no doubt that the tray would prove a much 

 more serious source of infection than the house itself. 



The practice of manuring mulberry land with silkworm faeces 

 might, it was thought, lead to the infection of the worms fed 

 on the leaf from plants thus manured, if the faeces contained 

 pebrine spores. The experiments— 3 in number — which were 

 undertaken to test this idea were rather unexpected in their 

 results, and I must confess that they do not appear to me to be 

 altogether trustworthy. Where the fault lies I am unable to deter- 

 mine, and I give the findings — Experiment 6, Appendix III — with 

 this caution. The material used in infecting the plot- was similar 

 to what was used to infect the house and trays. It was certainly 

 very heavily infective, but surely not sufficient to give a disease 

 percentage of over 80 in two of the lots. The second lot gave a 

 percentage of 11 '4 disease and that is possible, although even in 

 this case it is difficult to understand how the leaves growing on the 

 bushes, some little distance above the ground, ' could become con- 

 taminated sufficiently to produce even this amount of infection. 

 It is possible that in gathering the leaves they were laid on the ground 

 and thus got soiled with the pebrinised material used for manure. 

 I confess I expected to find only a very small amount of disease if 

 any at all in these experiments, and I cannot believe that the per- 

 centages given express the actual amount of infectivity. That 

 infection was picked up, however, seems certain, but I cannot under- 

 stand the high degree. In view of the result of this experiment 

 —doubtful though it is to some extent — it cannot be wise to con- 

 tinue manuring mulberry land with silkworm fasces. 



Still another source of infection to be noted is i_ diseased, worms 

 being reared alo ng .w ith healthy stock. A number of experiments 

 have^beenT'done ~ih~fche past which show that diseased caterpillars 

 are capable of spreading the disease to healthy caterpillars when 

 the two are reared together. Most of these experiments, however, 

 have been done by feeding some caterpillars with spores and then 

 mixing them with a healthy lot and the results have always given a 

 high percentage of disease. Two experiments of this type are given 



