DISEASE-GERMS. 257 



heifer, by inoculation with lymph which has been " humanized " by 

 long transmission through a succession of human beings. For, as is 

 proved by Dr. Martin's experiments on this ntfro-vaccination, such 

 lymph has been so altered by " humanization " that the germs it con- 

 tains do not properly reproduce themselves in the system of the calf, 

 thus showing that it no longer possesses the attributes of true vaccinia. 

 And, although the liability to contamination from human disease may 

 be thus greatly diminished, it can not be certainly said to have been 

 destroyed. 



We now come to the bearing of Pasteur's researches on the ques- 

 tion of the fundamental identity of small-pox and cow-pox, originally 

 mooted by Jenner. Attempts at its solution were made, early in the 

 present century, by the inoculation of bovine animals with small-pox 

 virus ; and it was asserted that in this way true vaccinia had been 

 artificially produced. But the evidence in support of this assertion 

 did not command general assent ; and it was not until Dr. Thiele, of 

 Kazan, published, about forty years ago, an account of his experiments, 

 that the doctrine obtained any considerable amount of acceptance. 

 According to the citations given by Mr. Simon, in his valuable " Re- 

 port on Small-pox and Vaccination," issued under Government au- 

 thority, in 1857, Dr. Thiele not only repeatedly succeeded in producing 

 a genuine vaccinia by inoculating bovine animals with small-pox 

 virus, but himself used this artificial vaccine largely and successfully 

 in human vaccination, and propagated it extensively by the instru- 

 mentality of other vaccinators, its protective power being found to be 

 fully equal to that of the natural vaccinia. But, further, Dr. Thiele 

 asserted that he could produce this artificial vaccine without the use 

 of the cow at all, by diluting the small-pox virus with warm milk, or, 

 as we should now term it, " cultivating " its living germs in that fluid. 

 I can scarcely help thinking that the great improbability as it then 

 seemed of such a conversion has thrown a discredit upon the whole 

 of Dr. Thiele's statements, which has caused them to be ignored by 

 most subsequent workers on this subject. But, should that part of his 

 results be ever confirmed, he must be accorded the credit of having 

 anticipated in a most remarkable way one of the most important of 

 Pasteur's methods, though, it is pretty certain, without knowing, or 

 even guessing, their true rationale ; for it must have been not by 

 dilution of the virus (like that of a chemically acting fluid), but by a 

 modification in the character of the disease-germs resulting from their 

 development in milk, that this part of Thiele's results (supposing them 

 to be genuine) was produced. 



Simultaneously with those of Dr. Thiele, a set of experiments of 

 the same kind was being carried on in our own country by Mr. Ceely, 

 of Aylesbury ; the results of which, however, were not equally satis- 

 factory. He did, it is true, produce an eruption in cows inoculated 

 with small-pox virus, which was transmissible by inoculation to the 

 TOL. xx. 17 



