x.] BIOGENESIS AND ABIOGENESIS. 247 



But the sacrifice has not been in vain. It is now 

 certain that this devastating, cholera-like, Pebrine is the 

 effect of the growth and multiplication of the Panhisto- 

 phyton in the silkworm. It is contagious and infectious, 

 because the corpuscles of the Panhistophyton pass away 

 from the bodies of the diseased caterpillars, directly or 

 indirectly, to the alimentary canal of healthy silkworms 

 in their neighbourhood ; it is hereditary, because the cor- 

 puscles enter into the eggs while they are being formed, 

 and consequently are carried within them when they 

 are laid ; and for this reason, also, it presents the very 

 singular peculiarity of being inherited only on the 

 mother's side. There is not a single one of all the appa- 

 rently capricious and unaccountable phenomena pre- 

 sented by the Pebrine, but has received its explanation 

 from the fact that the disease is the result of the pre- 

 sence of the microscopic organism, Panhistophyton. 



Such being the facts with respect to the Pebrine, what 

 are the indications as to the method of preventing it ? 

 It is obvious that this depends upon the way in which 

 the Panhistophyton is generated. If it may be generated 

 by Abiogenesis, or by Xenogenesis, within the silkworm 

 or its moth, the extirpation of the disease must depend 

 upon the prevention of the occurrence of the conditions 

 under which this generation takes place. But if; on the 

 other hand, the Panhistophyton is an independent organ- 

 ism, which is no more generated by the silkworm, than the 

 mistletoe is generated by the apple-tree or the oak on 

 which it grows, though it may need the silkworm for its 

 development in the same way as the mistletoe needs the 

 tree, then the indications are totally different. The sole 

 thing to be done is to get rid of and keep away the germs 

 of the Panhistophyton. As might be imagined, from the 

 course of his previous investigations, M. Pasteur was 

 led to believe that the latter was the right theory ; and, 



