268 BIOGENESIS AND ABIOGENESIS vill 



Such being the facts with respect to the Pebrine, 

 what are the indications as to the method of pre- 

 venting 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 inde- 

 pendent organism, 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 develop- 

 ment 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 inves- 

 tigations, 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 success- 

 ful 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 minute organisms 

 which are produced from pre-existing germs, or by 

 homogenesis ; and there is no reason, that I know 

 of, for believing that what happens in insects may 



