404 POISONS, CONTAGIONS, MUSMS. 



The production of matters of this kind, which 

 render the body susceptible of contagion, may be 

 occasioned by the manner of living, or by the nutri- 

 ment taken by an individual. A superabundance of 

 strong and otherwise wholesome food may produce 

 them, as well as a deficiency of nutriment, unclean- 

 liness, or even the use of decayed substances as 

 food. 



All these conditions for contagion must be con- 

 sidered as accidental. Their formation and accu- 

 mulation in the body may be prevented, and they 

 may even be removed from it without disturbing its 

 most important functions or health. Their presence 

 is not necessary to life. 



The action, as well as the generation of the matter 

 of contagion is, according to this view, a chemical 

 process participated in by all substances in the 

 living body, and by all the constituents of those 

 organs in which the vital principle does not over- 

 come the chemical action. The contagion, accord- 

 ingly, either spreads itself over every part of the 

 body, or is confined particularly to certain organs, 

 that is, the disease attacks all the organs or only a 

 few of them, according to the feebleness or intensity 

 of their resistance. 



In the abstract chemical sense, reproduction of a 

 contagion depends upon the presence of two sub- 

 stances, one of which becomes completely decom- 

 posed, but communicates its own state of transform- 

 ation to the second. The second substance thus 

 thrown into a state of decomposition is the newly- 

 formed contagion. 



The second substance must have been originally a 

 constituent of the blood : the first may be a body 

 accidentally present; but it may also be a matter 

 necessary to life. If both be constituents indispen- 

 sable for the support of the vital functions of certain 

 principal organs, death is the consequence of their 

 transformation. But if the absence of the one sub- 

 stance which was a constituent of the blood do not 



