1870.] BRITISH ASSOCIATION. 33^ 



ravages of the malady, and the inefficiency of the remedies which 

 liad been suggested, despatched M. Pasteur to study it, tliat the 

 question received its final settlement; at a great sacrifice, not only 

 of the time and peace of mind of that eminent philosopher, but, I 

 regret to have to add, of his health. 



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 Panhistophyton in the silkworm. It is 

 contagious and infectious because the corpuscles of the Panhisto- 

 phyton 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 corpuscles 

 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 

 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 , 

 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 Xeno 

 genesis, 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 organism, which 

 is no more generated by the silkworm than the mistletoe is gene- 

 rated by the oak, or the apple-tree, on which it grows, though it 

 may need the silkworm for its developement, in the same way as 

 the mistletoe needs the tree, then the indications are totally differ- 

 ent. 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 guided by that theory, 

 he has devised a method of extirpating the disease, which has 

 proved to be completely successful wherever it has been properly 

 carried out. 



There can be no reason, then, for doubting that, among insects, 

 contagious and infectious diseases of great malignity are caused by 



