POISONS, CONTAGIONS, MIASMS. 



121 



putrefying in the conditions afforded by the 

 body. 



It is impossible to mistake the modus ope- 

 randi of this poison, for Colin has clearly 

 proved that muscle, urine, cheese, cerebral 

 substance, and other matters, in a state of 

 putrefaction, communicate their own state 

 of decomposition to substances much less 

 prone to change of composition than the 

 blood. When placed in contact with a so- 

 lution of sugar, they cause its putrefaction, 

 or the transposition of its elements into car- 

 bonic acid and alcohol. 



When putrefying muscle or pus is placed 

 upon a fresh wound, it occasions disease 

 and death. It is obvious that these sub- 

 stances communicate their own state of pu- 

 trefaction to the sound blood from which they 

 were produced, exactly in the same manner 

 as gluten in a state ot decay or putrefaction 

 causes a similar transformation in a solution 

 of sugar. 



Poisons of this kind are even generated 

 by the body itself in particular diseases. In 

 small-pox, plague, and syphilis, substances 

 of a peculiar nature are formed from the 

 constituents of the blood. These matters 

 are capable of inducing in the blood of a 

 healthy individual a decomposition similar 

 to that of which they themselves are the 

 subjects ; in other words, they produce the 

 same disease. The morbid virus appears to 

 reproduce itself just as seeds appear to re- 

 produce seeds. 



The mode of action of a morbid virus ex- 

 hibits such a strong similarity to the action 

 of yeast upon liquids containing sugar and 

 gluten, that the two processes have been 

 long since compared to one another, al- 

 though merely for the purpose of illustra- 

 tion. But when the phenomena attending 

 the action of each respectively are con- 

 sidered more closely, it will in reality be 

 seen that their influence depends upon the 

 same cause. 



In dry air, and in the absence of mois- 

 ture, all these poisons remain for a long time 

 unchanged ; but when exposed to the air in 

 the moist condition, they lose very rapidly 

 their peculiar properties. In the former 

 case, those conditions are afforded which ar- 

 rrst their decomposition without destroying 

 it ; in the latter, all the circumstances neces- 

 sary for the completion of their decomposi- 

 tion are presented. 



The temperature at which water boils, 

 and contact with alcohol, render such poi- 

 sons inert. Acids, salts of mercury, sul- 

 phurous acid, chlorine, iodine, bromine, 

 aromatic substances, volatile oils, and parti- 

 cularly empyreumatic oils, smoke, and a 

 decoction of coffee, completely destroy their 

 contagious properties, in some cases com- 

 bining with them or otherwise effecting 

 their decomposition. Now all these agents, 

 without exception, retard fermentation, pu- 

 trefaction, and decay, and when present in 

 sufficient quantity, completely arrest these 

 processes of deco nposition. 

 16 



A peculiar matter, to which the poisonous 

 action is due, cannot, we have seen, be ex- 

 tracted from decayed sausages : and it is 

 equally impossible to obtain such a principle 

 from the virus of small-pox or plague, and 

 for this reason, that their peculiar power is 

 due to an active condition recognisable ny 

 our senses, only through the phenomena 

 which it produces. 



In order to explain the effects of conta- 

 gious matters, a peculiar principle of life has 

 been ascribed to them a life similar to that 

 possessed by the germ of a seed, which 

 enables it under favourable conditions to de- 

 velope and multiply itself. It would be im- 

 possible to find a more correct figurative 

 representation of these phenomena ; it is one 

 which is applicable to contagions, as well 

 as to ferment, to animal and vegetable sub- 

 stances in a state of fermentation, putrefac- 

 tion or decay, and even to a piece of decay- 

 ing wood, which by mere contact with fresh 

 wood, causes the latter to undergo gradually 

 the same change and become decayed and 

 mouldered. 



If the properly possessed by a body of 

 producing such a change in any other sub- 

 stance as causes the reproduction of itself, 

 with all its properties, be regarded as life, 

 then, indeed, all the above phenomena may 

 be ascribed to life. But in that case the} 

 must not be considered as the only processes 

 due to vitality, for the above interpretation 

 of the expression embraces the majority ^t' 

 the phenomena which occur in organic che - 

 mistry. Life would, according to that view, 

 be admitted to exist in every body in which 

 chemical forces act. 



If a body A , for example oxamide, (a sub- 

 stance scarcely soluble in water, and without 

 the slightest taste,) be brought into contact 

 with another compound B, which is to be 

 reproduced; and if this second body be oxalic 

 acid dissolved in water; then the following 

 changes are observed to take place : The 

 oxamide is decomposed by the oxalic acid, 

 provided the conditions necessary for their 

 exercising an action upon one another are 

 present. The elements of water unite with 

 the constituents of oxamide, and ammonia is 

 one product formed, and oxalic acid the 

 other, both in exactly the proper proportions 

 to combine and form a neutral salt. 



Here the contact of oxamide and oxalic 

 acid induces a transformation of the oxa- 

 mide, which is decomposed into oxalic acid 

 and ammonia. The oxalic acid thus formed, 

 as well as that originally added, are shared 

 by the ammonia or m other words, as 

 much free oxalic acid exists after the de- 

 composition as before it, und is of course 

 still possessed of its original power. It mat- 

 ters not whether the free oxalic acid is that 

 originally added, or that newly produced; 

 it is certain that it has been reproduced in an 

 equal quantity by the decomposition. 



If we now add to the same mixture a fresh 

 portion of oxamide, exactly equal in quan- 

 tity to that first used, and treat it in the same 



