REPORT ON THE DISEASES OP SILKWORMS IN INDIA 7^ 



completely. On the other hand the worms that showed symptoms 

 of disease had an acid gut (pH=2'6). 



A consideration of the. work of the various Japanese workers 

 and of the few experiments which I have made leads one to lay 

 stress on certain points. (1) Under healthy conditions silkworms 

 are not capable of being infected with flacherie by any of the or- 

 ganisms isolated from caterpillars that have died of this disease. 

 (2) The organisms found in the caterpillars suffering from flacherie 

 are common free-living bacteria that are normally always present 

 on mulberry leaves or in the air. (3) The conditions necessary for 

 infection seem to be a high temperature combined with a high 

 humidity. (4) The gut contents of a caterpillar suffering from 

 flacherie are always less alkaline than in a healthy caterpillar. 

 (5) The gut contents of a caterpillar subjected to high temperature 

 and humidity are less alkaline than in a worm under healthy condi- 

 tions — indeed they are of the same alkalinity as a worm suffering 

 from flacherie— but no bacteria or very few bacteria may be found 

 in these worms. 



These facts seem to justify one in coming to certain conclusions. 

 Flacherie is not caused by any one bacterium although certain 

 forms are more commonly got in diseased worms than others, and 

 experiments seem to show that these few bacteria when fed to cater- 

 pillars in large numbers and under certain conditions of tempera- 

 ture and humidity tend to produce flacherie very readily. Symp- 

 toms exactly corresponding to flacherie are sometimes got by 

 subjecting caterpillars to treatment which lessens the alkalinity of 

 the gut, and in these cases bacteria are frequently not present in 

 the gut. Under these circumstances it cannot be said that flacherie 

 is an infectious disease in the strict meaning of the term. 



•There is obviously a close connection between decreased alkalin- 

 ity of the gut and flacherie but it is not at all certain that bacterial 

 growth is the cause of this. Indeed the absence of bacteria in 

 some cases would rather militate against this view. It is sup- 

 posed that a high temperature and humidity are favourable condi- 

 tions for bacterial growth, and these, producing certain bye-products, 

 reduce the alkalinity of the gut. But it seems to me that the 

 evidence shows rather that the alkalinity of the gut is lessened by 

 some disturbance in the metabolism of the caterpillar, and that 

 this gives the bacteria normally present on the leaf a medium in 

 which they can multiply very rapidly. The caterpillar in the first 

 instance may be said to suffer from " acid indigestion ". In some 

 cases this may even cause death without the intervention of any 

 bacteria; normally, however, a multiplication of bacteria follows 

 upon this lessening of the extreme alkalinity of the gut — fermenta- 



