POISONS, CONTAGIONS, MIASMS. 



127 



But this substance may be again generated 

 in the same individual, so thai he may again 

 become liable to contagion, and a second or 

 a third vaccination will again remove the 

 peculiar substance 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. 



If it is assumed that chemical action and 

 the vital principle mutually balance each 

 other in the blood, it must farther be sup- 

 posed that the chemical powers will have 

 a certain degree of preponderance in the 

 lungs, where the air and blood are in imme- 

 diate contact; for these organs are fitted by 

 nature to favour chemical action ; they offer 

 no resistance to the changes experienced by 

 the venous blood. 



The contact of air with venous blood is 

 limited to a very short period of time by the 

 motion of the heart, and any change be- 

 yond a determinate point is, in a certain 

 degree, prevented by the rapid removal of 

 the blood which has become a-rterialised. 

 Any disturbance in the functions of the 

 heart, and any chemical action from with- 

 out, even though weak, occasions a change 

 in the process of respiration. Solid sub- 

 stances also, such as dust from vegetable, 

 animal, or inorganic bodies, act in the same 

 way as they do in a saturated solution of a 

 salt in the act of crystallization, that is, they 

 occasion a deposition of solid matters from 

 the blood, by which the action of the air 

 upon the latter is altered or prevented. 



When gaseous and decomposing sub- 

 stances, or those which exercise a chemical 

 action, such as sulphuretted hydrogen and 

 carbonic acid, obtain access to the lungs, 

 they meet with less resistance in this" organ 

 than in any other. The chemical process 

 of slow combustion in the lungs is accele- 

 rated by all substances in a state of decay 

 or putrefaction, by ammonia and alkalies ; 

 but it is retarded by empyreumatic sub- 

 stances, volatile oils, and acids. Sulphu- 

 retted hydrogen produces immediate decom- 

 position of the blood, and sulphurous acid 

 combines with the substance of the tissues, 

 the cells, and membranes. 



When the process of respiration is modi- 

 fied by contact with a matter in the pro- 

 gress of decay, when this matter commu- 

 nicates the state of decomposition, of which 

 it is the subject, to the blood, disease is pro- 

 duced. 



If the matter undergoing decomposition 

 is the product of a disease, it is called con- 

 tagion; but if it is a product of the decay 

 or putrefaction of animal and vegetable 

 substances, or if it acts by its chemical pro- 

 perties, (not by the state in which it is,) and 

 therefore enters into combination with parts 

 of the body, or causes their decomposition, 

 it is termed miasm. 



Gaseous contagious matter is a miasm 

 emitted from blood, and capable oJ gene- 

 rating itself again in blood 



I But miasm, properly so called, causes 

 disease without being itself reproduced. 



All the observations hitherto made upon 

 gaseous contagious matters prove, that they 

 also are substances in a state of decompo- 

 sition. When vessels filled with ice are 

 placed in air impregnated with gaseous con- 

 tagious matter, their outer surfaces become 

 covered with water containing a certain 

 quantity of this matter in solution. This 

 water soon becomes turbid, and in common 

 language putrefies, or, to describe the chanp-e 

 more correctly, the state of decomposition 

 of the dissolved contagious matter is com- 

 pleted in the water. 



All gases emitted from putrefying animal 

 and vegetable substances in processes of 

 disease, generally possess a peculiar nau- 

 seous offensive smell, a circumstance which, 

 in most cases, proves the presence of a body 

 in a state of decomposition. Smell itself 

 may in many cases be considered as a re- 

 action of the nerves of smell, or as a resist- 

 ance offered by the vital powers to chemical 

 action. 



Many metals emit a peculiar odour when 

 rubbed, but this is the case with none of 

 the precious metals, those which suffer no 

 change when exposed to air and moisture. 

 Arsenic, phosphorus, musk, the oils of lin- 

 seed, lemons, turpentine, rue, and pepper- 

 mint, possess an odour only when they are 

 in the act of eremacausis (oxidation at com- 

 mon temperatures.) 



The odour of gaseous contagious matters 

 is owing to the same cause ; but it is also 

 generally accompanied by ammonia, which 

 may be considered in many cases as the 

 means through which the contagious matter 

 receives a gaseous form, just as it is the 

 means of causing the smell of innumerable 

 substances of little volatility, and of many 

 which have no odour. (Robiquet.)* 



Ammonia is very generally produced in 

 cases of disease; it is always emitted in 

 those in which contagion is generated, and 

 is an invariable pioductof the decomposition 

 of animal matter. The presence of ammo- 

 nia in the air of chambers in which diseased 

 patients lie, particularly of those afflicted 

 with a contagious disease, may be readily 

 detected; for the moisture condensed by ice 

 in the manner just described, produces a 

 white precipitate in a solution of corrosive 

 sublimate, just as a solution of ammonia 

 does. The ammoniacal salts also, which 

 are obtained by the evaporation of rain- 

 water after an acid has been added, when 

 treated with lime so as to set free their am- 

 monia, emit an odour most closely resem- 

 bling that of corpses, or the peculiar smell 

 of dunghills. 



By evaporating acids in air containing 

 gaseous contagions, the ammonia is neu- 

 tralised, and we thus prevent further de- 

 composition, and destroy the power of the 

 contagion, that is, its state of chemical 



* Ann. de Chim. et de Phys. XV. 27. 



