42 Influence of Atmosphenc Pressure 



onersixth, in the atmospheric pressure, inq-y be receive^ as 

 proof, though less obvious, of the same fact.* 



But in less peculiar cases than these, notable effects may 

 occur, when the changes in the weight of the air are frequent, 

 sudden, and considerable, even v^ithin the ordinary range of at- 

 mospheric variation. Regarding merely the average pressure 

 upon the whole body, it is to be supposed that any very sudden 

 fluctuation, to the amount perhaps of one- thirtieth, may pro- 

 duce temporary changes in the balance of circulation between 

 external and internal parts, of much moment to the latter. 

 And these are particularly to be looked for, when there is in- 

 dividual liability to certain diseases, or close approach to them 

 at the time ; a point requiring to be kept in mind more than 

 it usually is, in estimating the influence of exciting causes, 

 whatever then' nature. 



This observation, as I have already stated, appears especially 

 to apply to aff*ections of the brain. I have made note of two 

 or three periods, since I began practice, during which there 

 has been a more than wonted frequency of apoplectic or para- 

 lytic seizures within my immediate knowledge ; so marked 

 as to make it difficult to attribute the fact to mere casu- 

 alty, notwithstanding the many circumstances which tend to 

 invalidate such results when not verified by large averages. 

 The same fact, observed by others, has generally been attri- 

 buted to external heat alone. But allowing what has already 

 been assigned to this cause, the particular character of the 

 weather at these times will scarcely support the inference ; nor 

 has the result in question been equally apparent even under 

 higher degrees of atmospheric temperature. While, on the 

 other hand, I have observed at these periods frequent and rapid 

 changes in the barometer, often with great depression of its 

 level ; and have noticed at the same time the very common 

 occurrence of lesser affections of the head, — vague and uneasy 

 sensations, oppression, vertigo, and what may be termed a feel- 



* Tlie suggestions of Sir James Murray (Report of the British Association, 

 1835J, for the use of artificially rarefied or condensed air, in application to 

 the surface of the body as a remedial agent, deserve much attention. The 

 cases are numerous, where changes in the local distribution of the blood, 

 thus rea4ily im^de, would b« of inuch value ia th^ treatment of disease. 



