600 Anatomy, Physiology, and Pathology of the 



The mingling of noxious matters will occasionally produce a 

 physical change in the air ; a remarkable instance of which is thus 

 described by Dr. Prout in his Bridgevvater Treatise.* He says 

 that — 



"He had for some years been occupied in investigations regarding the 

 atmosphere ; and for more than six weeks previously to the appearance of 

 cholera in London had almost everyday been engaged in endeavouring to 

 determine, with Ihe utmost accuracy, the weight of a given quantity of air 

 under precisely the same circumstances of temperature and pressure. On 

 a particular day, the 9th of February, 1832, the weight of the air suddenly 

 appeared to rise above the usual standard. As the rise was at the time 

 supposed to be the result of some accidental error, or of some derange- 

 ment in the apparatus employed, in order to discover the cause the suc- 

 ceeding observations were made with the most rigid scrutiny ; but no error 

 or derangement whatever could be detected. On the days immediately 

 following, the weight of the air still continued above the standard, though 

 not quite so high as on the 9th of February, when the change was first 

 noticed. The air retained its augmented weight during the whole time 

 these experiments were carried on ; namely, about six weeks longer. The 

 increase of the weight of the air observed in these experiments was small, 

 but still decided and real. The method of conducting the experiments 

 was such as not to allow of an error, at least to an amount so great as the 

 additional weight, without the cause of that error having become apparent. 

 There seems, therefore, to be only one mode of rationally explaining this 

 increased weight of the air at London, February, 1832; which is, by admit- 

 ting the diffusion of some gaseous body through the lower regions of the 

 atmosphere of this city considerably heavier than the air it displaced. 

 About the 9th of February the wind, which had previously been west, 

 veered round to the east, and remained chiefly in that quarter to the end 

 of the month. Now, precisely on the change of the wind the first cases of 

 cholera were reported in London : and from that time the disease con- 

 tinued to spread. That the epidemic cholera was the effect of the peculiar 

 condition of the atmosphere is more perhaps than can be safely main- 

 tained ; but reasons, which have been advauced elsewhere, lead the writer 

 of this treatise to believe that the virulent disease termed cholera was 

 owing to the same matter which produced the additional weight of the 

 air." 



I am not aware if any physical alterations of the atmosphere 

 have accom]>anied the present outbreak of Asiatic cholera ; but 

 the foregoing statements, together with the quotation I have just 

 made, are sufficient to establish the point that the air may be 

 vitiated by an admixture of various matters. 



By a careful investigation of epizootic diseases we become 

 acquainted with certain laws which govern their spread, as well 

 as with the secondary causes which predispose animals to their 

 attack. Some of these maladies are contagious or infectious, as 

 is the case with the small- pox of sheep, and may be also with 

 pleuro-pneumonia. Many an outbreak can be clearly traced to 

 diseased animals being brought upon the farm ; nevertheless this 

 is not a necessary consequence of such a procedure ; and very 



* Chemistry, Meteorology, and the Functions of Digestion considered with reference 

 to Natural Theology, by William Prout, M.D., F.K.S., &c., p. 353 et seq. 



