314 Mitchell on the Penetrativeness of Fluids. 



was powerfully inflated by its entrance, and yet as rapidly collapsed 

 when the gas was invited outwards by the presence of another gas 

 on its exterior. The resemblance of phenomena does not end here. 

 Each penetrates different substances with different degrees of facility, 

 and the quality of the surface is often to both as influential as the 

 character of the substance which affords it. The fact, the force, the 

 enlargement of bulk, the penetrativeness varying usually with the 

 substance and surface to be acted on, being however uniform rela- 

 tive to all gases, the constantly diminishing rate of progression, the 

 issuing out again when invited by new substances, or a vacuum, or 

 when mechanical compression is applied, all afford evidence of ana- 

 logy as perfect as is perhaps ever offered to the view of philosophy. 



We are struck with its resemblance to water in one respect. 

 Highly concentrated caloric invites the penetration of all liquids, 

 and perhaps of all solids ; and thus, while held in solution by it, 

 they obtain a penetrativeness themselves which does not naturally 

 belong to them, and are elevated into the atmosphere in spite of 

 specific gravity, however high, or of atomic weight, however consi- 

 derable. Some facts, not yet sufficiently studied, lead me to the 

 perhaps hasty conjecture, that even the decomposing influence of 

 caloric is owing to this power. Water exercises it in that way in 

 some cases, such as that of acetate of lead. 



The great length to which my remarks have unexpectedly ex- 

 tended, and the call of the printer, prevent me from going fully into 

 the consideration of the connexion of our experiments with patho- 

 logy and therapeutics. Their bearing on these departments of 

 medical science will furnish subject matter for a future essay. In 

 the mean time, we feel entitled to believe that we better comprehend 

 some of the phenomena of colic, tympanitis, and emphysema, and 

 see more clearly the cause of the value of certain methods of cure. 



Bichat was among the first to produce the passage of air of various 

 kinds into the blood-vessels and cellular tissue of the lungs, by forcin^ 

 it into the air-cells and there confining it. Even when the blood- 

 vessels were full of froth, and emphysema became extensive, he 

 could perceive not the slightest laceration of the bronchia?. When 

 the impulsion was moderate, the air passed only into the blood- 

 vessels; when more violent, its presence became manifest in the 

 cellular tissue. In certain cases referred to by authors., violent ex- 

 ertion, laborious respiration, and severe flatulency of the intestines, 

 have forced air into the blood-vessels and cellular tissue. Colic has 

 produced also tympanitis, and few practised physicians are ignorant 

 of the fact, that great gaseous distention of the abdomen hits disap- 



