sx.] SPONTANEOUS GENERATION. 3G9 



morbid growth and Xenogenesis would be effaced. 

 And I am inclined to think that the progress of dis- 

 covery lias almost brought us to this point already. I 

 have been favoured by Mr. Simon with an early copy 

 of the last published of the valuable "Reports on the 

 Public Health," which, in his capacity of their medical 

 officer, he annually presents to the Lords of the Privy 

 Council. The appendix to this report contains an in- 

 troductory essay " On the Intimate Pathology of Con- 

 tagion," by Dr. Burdon Sanderson, which is one of the 

 clearest, most comprehensive, and well-reasoned dis- 

 cussions of a great question which has come under my 

 notice for a long time. I refer you to it for details and 

 for the authorities for the statements I am about to 

 make. 



You are familiar with what happens in vaccination. 

 A minute cut is made in the skin, and an infinitesimal 

 quantity of vaccine matter is inserted into the wound. 

 Within a certain time a vesicle appears in the place of 

 the wound, and the fluid which distends this vesicle is 

 vaccine matter, in quantity a hundred or a thousand- 

 fold that which was originally inserted. ISTow, what 

 has taken place in the course of this operation % Has 

 the vaccine matter, by its irritative property, produced 

 a mere blister, the fluid of which has the same irrita- 

 tive property? Or does the vaccine matter contain 

 living particles, which have grown and multiplied 

 where they have been planted ? The observations of 

 M. Chauveau, extended and confirmed by Dr. Sander- 

 son himself, appear to leave no doubt upon this head. 

 Experiments, similar in principle to those of Helmholtz 

 on fermentation and putrefaction, have proved that the 

 active element in the vaccine lymph is non-diffusible, 

 and consists of minute particles not exceeding $0 / J00 th 

 of an inch in diameter, which are made visible in the 



