240 ANNUAL OF SCIENTIFIC DISCOVERY. 



take up food. By the use of disinfecting agents, Mr. M'Dougall Las 

 been able to feed sheep and cattle, and retain them in health, on 

 meadows constantly wet by irrigation with liquid manure. The 

 disinfectant used is from the products of the distillation of tar ; the 

 amount required is small. Animal life is rapidly destroyed by it, 

 and chemical decomposition is stayed. All climates can furnish this 

 where coal lies or where trees grow. 



It would be possible to irrigate great districts at a very small ex- 

 pense. The result would be as certain on a large scale as on a small 

 one ; and it is probable that, in some cases, one or two applications 

 would be sufficient, for a long period at least. By the new state of 

 things destructive insects would also be destroyed. This new method 

 is especially applicable to other countries, and to more violent stages 

 of the disease. The author hopes to have it tried on extensive dis- 

 tricts in Italy. The method arose out of an advice everywhere neg- 

 lected, but still cherished as true, to disinfect whole cities by begin- 

 ning with the sewers, the origin and reservoir of all the mischief. 



The author believes that he has shown that decomposition, to a 

 most pernicious extent, is possible in soils ; that this is not a mere 

 opinion, but a fact readily demonstrated ; but that decomposition 

 may be arrested artificially to the preservation of health without the 

 destruction of vegetation ; and that in these facts we have not only 

 a surer basis in our reasonings on the origin of malaria, but an almost 

 certain process for its ultimate and total extermination. 



Cause of Malaria. The well-known chemist, Boussingault, re- 

 cently presented a paper to the French Academy, in which he stated 

 that carbonic oxide is developed in connection with oxygen whenever 

 the sun shines upon vegetable matter submerged in water impreg- 

 nated with carbonic acid. The presence of so deleterious a gas as 

 carbonic oxide in the atmosphere of marshy countries, as manifested 

 by this discovery, might, he thought, give a clue to the origin of the 

 diseases which are prevalent in districts exposed to marshy exhala- 

 tions. 



CHEMICAL AND PHYSICAL MODIFICATIONS OF THE ATMOS- 

 PHERE CONSEQUENT ON HABITATION. 



The repeated observations of chemists have taught us to regard the 

 identity of composition of the atmosphere as a fixed law, one to 

 which no exception is to be found in nature, unless it be in the 

 neighborhood of tropical rivers, where vast quantities of organic 

 matter, the debris of a luxuriant vegetation, are rapidly passing into 

 decomposition. Everywhere, whether collected on the top of Mont 

 Blanc, on the banks of the Seine or Thames, or in the middle of the 

 Atlantic, the two main constituents of the atmosphere are found in 

 precisely the same proportion, and the more perfect the processes of 

 analysis have become, the firmer has the constancy of this relation 

 been established. This fact has always, however, been rebelled 

 against by the common experience of mankind ; it has been almost 

 an opprobrium to science that, in spite of the manifestly different 

 feeling of the air on the Swiss mountains and in the middle of Lon- 

 don, the. chemist can detect no difference in composition. During 



