112 SCIENTIFIC REPORTS OF THE AGRICULTURAL RESEARCH 



an obviously diseased condition has been produced in the 

 worms as a result of the use of such infective material. 

 This may require several weeks' incubation during which 

 the difficulty of ensuring the absence of other sources of 

 infection and the possibility of adventitious disease in the 

 controls, add uncertainties to the results and make numer- 

 ous duplicates necessary. 



Infection through contagion or ingestion of the 

 parasite. The necessity of work upon this second source 

 of the disease will be realized when it is pointed out that 

 perfectly healthy seed if reared in infected surroundings 

 will give rise to worms which may die whilst still in the 

 larval stage, before spinning; it is the loss of time and the 

 money thrown away upon feeding such worms for several 

 weeks that has caused many thousands of silkworm rearers 

 to forsake this avocation in favour of some less precarious 

 mode of earning a livelihood. Numerous experiments 

 under controlled conditions have confirmed my previously 

 expressed conclusion that the principal, if not the only, 

 means of infection other than by hereditary transmission 

 is by ingestion of the spore form of the parasite with the 

 food. In this country at any rate, there seems to be no 

 need at present to assume that any other method is of seri- 

 ous consequence; the prime importance of avoiding this one 

 alone, and the great inherent difficulties of doing so, will 

 sufficiently engage the attention of rearers for some years 

 to come. 



Experiment here has not only shown the infective nature 

 of the pebrine spore, in India as in Europe, but has demon- 

 strated its presence in great numbers in the dust of rearing 

 houses and what is still more important in that of seed 

 selection buildings. Most of these loose spores are thrown 

 out of the gut of the infected but still feeding worm, along 

 with the feces, and being present in the latter in enormous 

 numbers remain to some extent upon the leaves upon which 

 the diseased and healthy worms alike are feeding. This 

 naturally results in their passing with the food into the 

 gut of the hitherto uninfected worms to act as sources of 

 disease. Thus hereditary infection of a small percentage 



