xv.] SPONTANEOUS GENERATION. 375 



directly or indirectly, to the alimentary canal of 

 healthy silkworms in their neighbourhood; it is he- 

 reditary, because the corpuscles enter into the eggs 

 while they are being formed, and consequently are car- 

 ried within them when they are laid ; and, for this rea- 

 son, 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 apparently capricious and 

 unaccountable phenomena presented by the Pebrine, 

 but has received its explanation from the fact that the 

 disease is the result of the presence of the microscopic 

 organism, Panldstopliyton. 



Such being the facts with respect to the Pebrine, 

 what are the indications as to the method of prevent- 

 ing it ? It is obvious that this depends upon the way 

 in which the Panldstopliyton is generated. If it may 

 be generated by Abiogenesis, or by Xenogenesis, within 

 the silkworm or its moth, the extirpation of the dis- 

 ease must depend upon the prevention of the occurrence 

 of the conditions under which this generation takes 

 place. But if, on the other hand, the Panliistopliyton 

 is an independent organism, which is no more generated 

 by the silkworm than the mistletoe is generated by the 

 oak or the apple-tree 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 indica- 

 tions are totally different. The sole thing to be done 

 is, to get rid of and keep away the germs of the Pan- 

 liistopliyton. 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, 

 guided by that theory, he has devised a method of ex- 

 tirpating the disease, which has proved to be com- 

 pletely successful wherever it has been properly car- 

 ried out 



