POISONS, CONTAGIONS, MIASMS. 



123 



weakest, in respect to active chemical cha- 

 racter. By virtue of this disposition, simple 

 compounds produce changes in every body 

 which offers no resistance to their action; 

 they enter into combination and cause de- 

 composition. 



The vital principle opposes to the con- 

 tinual action of the atmosphere, moisture 

 and temperature upon the organism, a re- 

 sistance which is, in a certain degree, invin- 

 cible. It is by the constant neutralization 

 and renewal of these external influences 

 that life and motion are maintained. 



The greatest wonder in the living organ- 

 ism is the fact that an unfathomable wisdom 

 has made the cause of a continual decom- 

 position pr destruction, namely, the support 

 of the process of respiration, to be the means 

 of renewing the organism, and of resisting 

 all the other atmospheric influences, such 

 as those of moisture and changes of tem- 

 perature. 



When a chemical compound of simple 

 constitution is introduced into the stomach, 

 or any other part of the organism, it must 

 exercise a chemical action upon all sub- 

 stances with which it comes in contact ; for we 

 know the peculiar character of such a body 

 to be an aptitude and power to enter into 

 combinations and effect decompositions. 



The chemical action of such a compound 

 is of course opposfed by the vital principle. 

 The results produced depend upon the 

 strength of their respective actions : either 

 an equilibrium of both powers is attained, 

 a change being effected without the destruc- 

 tion of the vital principle, in which case a 

 medicinal effect is occasioned ; or the acting 

 body yields to the superior force of vitality, 

 that is, it is digested; or lastly, the chemical 

 action obtains the ascendency and acts as a 

 poison. 



Every substance may be considered as 

 nutriment, which loses its former properties 

 when acted on by the vital principle, and 

 does not exercise a chemical action upon the 

 living organ. 



Another cla^s of bodies change the direc- 

 tion, the strength, and intensity of the re- 

 sisting force, (the vital principle,) and thus 

 exert a modifying influence upon the func- 

 tions of its organs. They produce a dis- 

 turbance in the system, either by their pre- 

 sence, or by themselves undergoing a change ; 

 these are medicaments. 



A third class of compounds are called 

 poisons, when they possess the property of 

 uniting with organs or with their component 

 parts, and when their power of effecting 

 this is stronger than the resistance offered 

 by thp vital principle. 



The quantity of a substance and its con- 

 dition must, obviously, completely change 

 the mode of its chemical action. 



Increase of quantity is known to be equi- 

 valent to superior affinity. Hence a medica- 

 ment administered in excessive quantity may i 

 act as a poison, and a poison in small doses 

 as a medicament. 



Food will act as a poison, that is, i. will 

 produce disease, when it is able to exercise 

 a chemical action by virtue of its quantity ; 

 or, when either its condition or its presence 

 retards, prevents, or arrests the motion ot 

 any organ. 



A compound acts as* a poison when all the 

 parts of an organ with which it is brought 

 into contact enter into chemical combination 

 with it, while it may operate as a medicine, 

 when it produces only a partial change. 



No other component part of the organism 

 can be compared to the blood, in respect of 

 the feeble resistance which it offers to exte- 

 rior influences. The blood is not an organ 

 which is formed, but an organ in the act of 

 formation ; indeed, it is the sum of all the 

 organs which are being formed. The che^ 

 mical force and the vital principle hold each 

 other in such perfect equilibrium, that every 

 disturbance, however trifling, or from what- 

 ever cause it may proceed, effects a change 

 in the blood. This liquid possesses so little 

 of permanence, that it cannot be removed 

 from the body without immediately suffer- 

 ing a change, and cannot come in contact 

 with any organ in the body, without yielding 

 to its attraction. 



The slightest action of a chemical agent 

 upon the blood exercises an injurious influ- 

 ence ; even the momentary contact with the 

 air in the lungs, although effected through 

 the medium of cells and membranes, alters 

 the colour and other qualities of the blood. 

 Every chemical action propagates itself 

 through the mass of the blood ; for exam- 

 ple, the active chemical condition of the 

 constituents of a body undergoing decom- 

 position, fermentation, putrefaction, or de- 

 cay, disturbs the equilibrium between the 

 chemical force and the vital principle in the 

 circulating fluid. Numerous modifications 

 in the composition and condition of the 

 compounds produced from the elements of 

 the blood, result from the conflict of the vital 

 force with the chemical affinity, in their in - 

 cessant endeavour to overcome one another. 



All the characters of the phenomena of 

 contagion tend to disprove the existence of 

 life in contagious matters. They without 

 doubt exercise an influence very similar to 

 some processes in the living organism; but 

 the cause of this influence is chemical ac- 

 tion, which is capable of being subdued by 

 other chemical actions, by opposed agencies. 



Several of the poisons generated in the 

 body by disease lose all their power when 

 introduced into the stomach, but others are 

 not thus destroyed. 



It is a fact very decisive of their chemical 

 nature and mode of action, that those poi- 

 sons which are neutral or alkaline, such as 

 the poisonous matter of the contagious fever 

 in cattle (typhus conta^iosm ruminantium.) 

 or that of the srnail-pox, lose their whole 

 power of contagion in the stomach ; whilst 

 that of sausages, which has an acid reac- 

 tion, retains all its frightful properties under 

 the same circumstances. 



