382 POISONS, CONTAGIONS, MIASMS. 



stituent of the blood is destroyed by a peculiar process of decom- 

 position, which does not affect the other constituents of the circu- 

 lating fluid. 



If the manner in which the precipitated yeast of Bavarian beer 

 acts be called to mind, the modus operandi of vaccine lymph can 

 scarcely be matter of doubt. 



Both the kind of yeast here referred to and the ordinary 

 ferment are formed from gluten, just as the vaccine virus and 

 the matter of small-pox are produced from the blood. Ordinary 

 yeast and the virus of human small-pox, however, effect a 

 violent tumultuous transformation, the former in vegetable 

 juices, the latter in blood, in both of which fluids respectively 

 their constituents are contained, and they are reproduced from 

 these fluids with all their characteristic properties. The preci- 

 pitated yeast of Bavarian beer, on the other hand, acts entirely 

 upon the sugar of the fermenting liquid, and occasions a very 

 protracted decomposition of it, in which the gluten which is 

 also present takes no part. But the air exercises an influence 

 upon the latter substance, and causes it to assume a new form 

 and nature, in consequence of which this kind of yeast also is 

 reproduced. 



The action of the virus of cow-pox is analogous to that of the 

 low yeast ; it communicates its own state of decomposition to a 

 matter in the blood, and from a second matter is itself regene- 

 rated, but by a totally different mode of decomposition ; the pro- 

 duct posse&ses the mild form, and all the properties of the lymph 

 of cow-pox. 



The susceptibility of infection by the virus of human small- 

 pox must cease after vaccination, for the substance to the pre- 

 sence of which this susceptibility is owing has been removed 

 from the body by a peculiar process of decomposition artificially 

 excited. But this substance may be again generated in the same 

 individual, so that he may again become liable to contagion ; and 

 a second or third vaccination will again remove the peculiar sub- 

 stance from the system. 



Chemical actions are propagated in no organs so easily as in 

 the lungs ; and it is well known that diseases of the lungs are, 

 above all others, frequent and dangerous. 



