REPORT ON THE DISEASES OF SILKWORMS IN INDIA 23 



application of the above life-history and see in actual practice how 

 much infection is actually picked up by healthy worms in disease- 

 infected houses, what the serious sources of infection are, what the 

 duration of infection is, what means can be used to prevent infection 

 and so on. But before turning to those questions there is one small 

 point in connection with the above life-history that may be noted 

 — the time in which the cycle can be completed, the life-cycle 

 being from planont to spore. 



In N. G. Mukerji's " Handbook of Sericulture " the portion 

 dealing with diseases is somewhat imperfect and misleading — partly 

 because in the day when it was written our knowledge of the subject 

 was very rudimentary, but also because there is a considerable 

 amount of faulty observation in it. The account of the develop- 

 ment is very far from correct, but the most serious mistake is the 

 amazing statement that " it takes about 20 days for the germs of 

 pebrine to attain the corpuscular shape." The truth of the matter 

 is that spores are formed in large numbers in an incredibly short 

 space of time.* Some worms fed with spores on the first of Septem- 

 ber and killed on the fifth had their gut-wall cells full of spores as 

 well as developing meronts, that is to say four days after infection 

 spores had been formed in large numbers (Plate VII, fig. 2). In 

 colder weather development is slower, but spores can always be 

 found a week at longest after infection — of course they may not be 

 numerous, that depends on the amount of the original infection. It 

 is important to recognize clearly the rapidity of spore formation 

 under ordinary conditions because much has been made of the neces- 

 sity for delaying moth examination until the last possible moment. 

 This, I believe, is not so extremely important as is thought, for 

 owing to the rapidity of spore formation it is certain that if the 

 worms were infected — and it is of course only the worms that can be 

 infected — by the time the pupal stage has been gone through and 

 the moth cuts out there will be a large number of spores present in 

 the body. Indeed if one examines a large number of pupae from 

 infected worms one will see that spores are abundant but meronts 

 are on the whole much less common. Thus when the moths emerge, 

 if they are infected they ought to have sufficient spores- present in 

 their gut and other organs to show the infection easily. The pupal 

 period is at shortest a week, so that if a caterpillar were infected on 

 the day before spinning there would be ample time for the meronts 

 to turn into spores before the moth emerged. 



Amount* of disease in ' India. It would seem to be the obvious 

 thing in any inquiry into a disease of this kind to institute a census 



* Stempell found spore formation after three days. 



