AND ITS RELATIONS TO THE LIVING ORGANISM. 285 



can be drawn ; and the train of symptoms produced by the operation of the 

 former, is really as much a disease as that which results from the presence 

 of the latter. The connection is, in fact, established by those "animal poi- 

 sons" which are the result of decomposition either within or without the 

 body ; such as that of the " pustule maligne," or of the flesh of animals 

 suffering under disease on the one hand, or the "cheese poison," etc., on the 

 other. It may be admitted that our belief in a specific material cause for 

 a great part of the effects set dow r n to the action. of "morbid poisons" is 

 merely inferential ; and there are many persons to whom their exhibition in 

 a tangible form seems to afford the only convincing evidence of their exist- 

 ence. But it must be remembered that the germs of other ferments con- 

 stantly exist in the state of suspension in the atmosphere, as is Avell shown 

 by the experiments of Schroder 1 and Pasteur, 2 who found that the mere fil- 

 tration of air through so coarse a medium as a plug of cotton-wool placed 

 in the mouth of the vessel, was sufficient to prevent the fermentation or 

 putrefaction of almost any organic substance which had been heated to boil- 

 ing, and it is easy to conceive that pus-cells, 3 or the minute insoluble parti- 

 cles of albuminous substance believed by Chauveau* to constitute the active 

 agents in the communication of the vaccine virus, or the minute portions of 

 the plasma of various diseases, may be taken up during evaporation and 

 remain long floating in the atmosphere. In the case of those poisons which 

 are capable of being introduced by inoculation, we have, indeed, the required 

 proof of their material existence ; and this proof is capable of being ex- 

 tended by a safe analogy to infectious diseases generally. For, if small-pox 

 can be communicated by the inhalation of an atmosphere tainted with the 

 exhalations of a person already affected with it, as well as by the introduc- 

 tion of the fluid of the cutaneous pustule into the blood of another, it can 

 scarcely admit of a question, that the same poisonous agent is transmitted 

 in both cases, although through different media, and that it has as real an 

 existence in the transferred air as in the transferred liquid. Diseases, then, 

 which are capable of being transmitted in both these methods, form the con- 

 necting link between those resulting from ordinary toxic agents, and those 

 which must be assumed to depend upon a subtle poison, of which the air 

 alone is the vehicle, such, for example, as malarious fevers; this assump- 

 tion being required by all the rules of logic, as the only one which will ac- 

 count for the phenomena to be explained, and therefore possessing a claim 

 to be accepted as an almost certain truth. There is a strongly marked dif- 

 ference, however, between the modus operandi of the toxic agents whose 

 action has been previously examined, and that of the morbid poisons we are 

 now considering ; for whilst the former possess a certain definite action, the 

 intensity of which (cceteris paribus) is proportionate to the quantity that is 

 in operation, and which is usually determined, in virtue of the " elective 

 affinity" already spoken of, to some particular organ or tissue, the latter 

 act primarily upon the 'blood, influencing the system at large through the 

 changes which they produce in its constitution ; and their potency depends 

 rather upon the susceptibility of the blood to their peculiar influence, than 

 upon the quantity of the poison that may be introduced into it. 



223. Of the existence of such susceptibility as a "predisposing cause" of 

 Zymotic^ disease there cannot be the slightest doubt. In the case of the Ex- 



1 Liebig, Annalen, cix, Heft i. 



2 Revue des Cours Scicntifiques, 1864, No. 21. 



3 See the experiments of Dr. Eiselt, of Prague, referred to in Med.-Chir. Rev., Oct. 

 1865, p. 523. 



4 Comptes Rendus, 1868, and Revue Scientifique, t. x, 1872, p. 68. 



5 The term zymotic is a very convenient designation, which, originally suggested 



