x.] BIOGENESIS AND ABIOGENESIS. 241 



while, finally, in those terrible structures known as 

 cancers, the abnormal growth has acquired powers of 

 reproduction and multiplication, and is only morpho- 

 logically distinguishable from the parasitic worm, the 

 life of which is neither more nor less closely bound up 

 with that of the infested organism. 



If there were a kind of diseased structure, the histo- 

 logical elements of which were capable of maintaining a 

 separate and independent existence out of the body, it 

 seems to me that the shadowy boundary between morbid 

 growth and Xenogenesis would be effaced. And I am 

 inclined to think that the progress of discovery has 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 " Eeports on the Public Health," which, 

 in his capacity of their medical officer, he annually pre- 

 sents to the Lords of the Privy Council. The appendix 

 to this report contains an introductory essay " On the Inti- 

 mate Pathology of Contagion," by Dr. Burdon-Sanderson, 

 which is one of the clearest, most comprehensive, and 

 well-reasoned discussions 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 thousandfold 

 that which was originally inserted. Now 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 irritative 

 property? Or does the vaccine matter contain living 



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