172 WRITINGS OF JOSEPH HENRY. [1855- 



The presence of organic matter may be detected in the 

 process just described by dropping into the water a little sul- 

 phuric acid and by afterwards evaporating the fluid we will 

 obtain traces of carbon. If the experiment, for example, be 

 made in a slaughter-house, comparatively a large amount of 

 this substance will be obtained ; and yet from abundant ob- 

 servation it is known that the animal effluvia to which the 

 butcher is constantly exposed are not of a morbific character, 

 since the followers of this occupation are proverbially healthy. 

 It would appear from this fact that the hurtful miasma is of 

 vegetable not of animal origin. That collected by Regnault 

 had the odor of burnt plants when incinerated. The same 

 investigator asserts that a marshy odor does not always in- 

 dicate feverish infection, and that in malarious districts it 

 was above all to be feared at times when the air appeared 

 pure and inodorous. From all the facts then, it appears 

 most probable that the substance called miasma is an organi- 

 zed body, endowed with life, and first generated in the de- 

 composition of aquatic vegetation ; that its introduction into 

 the circulation of animals is a real innoculation affecting 

 especially the nervous system ; finally, that when it com- 

 mences itself to decay in the open air it ceases to be dele- 

 terious, though it gives rise to disagreeable odors. This in- 

 vestigation opens a wide field for chemical research, to which 

 the later improvements in the art of analysis may perhaps 

 be successfully applied. Whatever may be the cause of the 

 disease spoken of experience has indicated the following pre- 

 cautions for those exposed to its influence: 



1st. In malarious districts, going out before the dew has 

 evaporated, should be as much as possible avoided. 



2d. Before exposure to the morning air breakfast should 

 be taken, or some slightly exciting drink, such as coffee or 

 tea, rather than spirits. The former produces a healthful 

 exhilaration, which prevents an attack of the miasma, while 

 the re-action which succeeds the exhilarating effects of the 

 latter tends to favor the absorption of the poison. 



3d. Flannel garments should be worn next to the body, as 

 these tend to stimulate the skin and prevent the deleterious 

 effect. 



