INSTITUTE, PUSA, FOR 1916-17 llfr 



climatic conditions either by confining rearing to certain 

 seasons or to certain districts. It might be possible to- 

 make use of this line of enquiry to elucidate what appears- 

 to me to be a problem of great importance in dealing with 

 preventive measures, not only for this but for manv other 

 parasitic infections, especially those of cultivated crops- 

 Many parasites, both animal and plant, go through a rest- 

 ing stage in their life-cycle, frequently in the spore form,, 

 as in the case of Nosema and of many bacteria and fungi i 

 this resting condition usually serves the purpose of carry- 

 ing the' organism through a period of existence during 

 which its surroundings are unfavourable for continued 

 vegetative activity, either by reason of failure of food 

 supply or of seasonal or climatic changes. Emergence 

 from the spore condition normally takes place when condi- 

 tions once more become favourable for active growth, and 

 the time of such emergence is generally determined by the 

 coincidence of some natural stimulus with such favourable 

 surroundings. In the case of the pebrine spore the ordin- 

 ary stimulus seems to be the combination of moisture and 

 suitable temperature found in the gut of the silkworm, 

 which initiates the series of internal changes in the spore, 

 culminating, under the added influence of acid found in the 

 gut, in the protrusion of the flagellum and the emergence of 

 the amcebula. It seems probable that the deleterious 

 effects of continued moisture upon the vitality of the spore 

 may be due to prematurely induced resumption of vital 

 activity in the latter, not indeed carried so far as germin- 

 ation, in the absence of other necessary stimuli, but result- 

 ing, in the absence of appropriate environment for its con- 

 tinuation, in either partial or total loss of vitality. Other 

 similar cases of abortive germination are common in nature r 

 and it would appear to be worth while to make a careful 

 study of the possibility of artificially inducing it in such 

 a way as to destroy various parasitic organisms, in cases 

 where the use of antiseptics or heat is not practicable. It 

 might, for instance, be found possible to induce premature 

 activity in the pebrine spores infesting rearing houses, 

 simply by moistening the walls and floor at a time of year 



