THE ORIGIN AND PROPAGATION OF DISEASE. 241 



dose of infectious blood so diluted that it represented only oue-trillionth 

 part of a drop. Vulpian* injected a rabbit with infectious serum, and 

 produced death in twenty hours. A second rabbit was inoculated with 

 the blood of the first, diluted to ^\, aud died in twenty-four hours. A 

 third rabbit was inoculated with the blood of the second, diluted to joVo? 

 and died in twenty-three hours. A fourth animal, inoculated with the 

 blood of the third, diluted to jodoooo? ^^^^ ^^ fifty-two hours; while the 

 fifth, inoculated with a dilution of toooooooooj became ill, but finally 

 recovered. 



In cases of septiccemia, therefore, the Bacteria really multiply in the 

 circulation during life ; and the small quantity of infectious blood neces- 

 sary to produce the disease is explained by their singular activity of 

 reproduction. 



These experiments certainly bring the study of morbid contagion into 

 very close relationship with that of putrefaction and fermentation 5 and 

 there is no doubt that the. analogies between them become more distinct 

 and suggestive at every step of the investigation. It only remains to 

 show that the same results will apply to diseases of more regular type 

 and more familiar occurrence. 



If we were to choose any single morbid affection as a fair represent- 

 ative of the whole class of contagious disorders, I suppose small-pox 

 would be the one selected. Its virulence, the certainty of its communi- 

 cation, the abundance of infectious matter generated, the regularity of 

 its symptoms, and the definite periods of its incubation and develop- 

 ment, all make it, so to speak, a kind of exponent of the essential quali- 

 ties of infectious disease. Besides this, its singular relations to vaccine 

 give it a peculiar interest; and the vaccine affection also, though 

 milder in its symptoms, is hardly less marked as a contagion than small- 

 pox itself. Conclusions derived from experiments with either must be 

 of great value in regard to the study of contagion as a whole. 



The first definite experiments in regard to the contagion of vaccine 

 we owe, I think, to Chauveau.t He endeavored to ascertain whether the 

 contagious principle of vaccine lymph is in its liquid or in its solid 

 portions. For this purpose he treated vaccine lymph by the process of 

 diffusion. The result showed that the contagious property of the lymph 

 does not reside in its liquid part, but in its solid corpuscles and granu- 

 lations. The liquid withdrawn by diffusion, though always found tO' 

 contain abundance of albuminous matter in solution, failed when used 

 for vaccination; while that containing the solid granules possessed its 

 normal activity and succeeded as fully as the fresh lymph. The residta 

 of these diffusion experiments were confirmed by those of Dr. Burdon- 

 Sanderson,! jjerformed subsequently. 



Chauveau also adopted a second i)lan for investigating the same point,. 



* Gazette Medicale de Paris, 1873, No. 3, p. 30. ' 



t " Comptes Rendus de l'Acad6inie des Sciences," 1868, tome Ixvi, p. 289. 

 t "Twelfth Report of tlie Medical Officer of the Privy Council," London,. 1870, pp^ 

 233, 235. 



l(j S 



