REPORT ON THE DISEASES OF SILKWORMS IN INDIA 25 



tains records of examinations of seed reared by the ryots themselves. 

 reared by the ryots under the supervision of the department, and 

 in the Government farms. The latter is a record of nursery stock 

 alone. It will be found that Nosema bombycis is always present in 

 a greater or lesser degree — usually not more than 6 or 8 per cent, as a 

 rule, but sometimes, as in August 1919 in Berhampore, rising as high 

 as 1 to 20 per cent. I am inclined to think that some of these higher 

 percentages require an explanation : either there has been a great 

 deal of infection in the rearing houses or the examinations made 

 of the parent moths have not been very careful. I am of the opinion 

 that the latter is the true explanation, as I have found by rearing 

 very carefully examined seed in the Berhampore Central Nursery 

 that little or no disease is picked up in the houses there (Appendix 

 I A, lots 2 — 4, 10, 16 and 21). There is, however, obviously a per- 

 centage — somewhere ranging between 2 and 6 per. cent. — below 

 which it seems to have been impossible so far to get infections of 

 Nosema reduced in the nurseries. 



I believe this percentage represents the amount of Nosema infec- 

 tion missed in the previous examination and not fresh infection 

 picked up in the rearing houses. It can hardly be called " disease " 

 for it has shown itself only in microscopic examination, and these 

 moths are comparable in a way with the " amoebic carrier "—a 

 person who may not have suffered from amoebic dysentery yet shows 

 the organism in his stools. Such a percentage of infection could, 

 of course, be eliminated or reduced to a completely negligible 

 amount by very painstaking examinations. It is a question as to 

 what will be profitable : a small percentage of Nosema infection at 

 certain examination cost or a smaller percentage at an increased cost. 

 In any case the amount of Nosema infection is not to be greatly 

 dreaded, provided the seed is reared under reasonably good condi- 

 tions and for one generation only. 



In Pusa where experimental rearing has been going on for some 

 time disease is practically non-existent. In hundreds of controls 

 examined, the percentage of pebrine found is so small as to be abso- 

 lutely negligible (Appendix I D). 



Here then we have a considerable body of facts to go upon, and 

 from these we can draw the following conclusions : — 



1. In ordinary village stock pebrine is appallingly abundant. 



2. In carefully examined, carefully reared stock, such as has been 

 used for experimenting in Pusa and in Kalimpong, disease is practi- 

 cally entirely absent. 



3. In nursery stock there seems to be relatively little disease — 

 at best none at all, at worst about 8 per cent. 



