Mitchell on the Penetrativeness of Fluids. 315 



peared without the apparent escape of any wind. When we con- 

 sider attentively the laws by which are regulated the entrance and 

 exit of gases under the action of their penetrativeness, we feel 

 scarcely at a loss to understand these phenomena. 



The prodigious accumulation of gas in the stomechiand bowels, in 

 hysteria and epilepsy, may be explained, by supposing- the air, which 

 exists by infiltration in every part of the animal economy, to be 

 forced by the violent compression of spasmodic action into the hol- 

 low viscera, where already existent gases invite its entrance. In 

 some experiments on the effect of certain gases on living cavities, 

 made by my ingenious friend Dr. Finley, their escape was so rapid 

 as to create surprise *. 



The establishment of the fact of the penetration of liquids, each 

 according to its peculiar rate, and the modifications of that rate 

 dependent on extrinsic force, such as impulsion or invitation, electri- 

 city, &c. teach us many valuable lessons both in philosophy and 

 medicine. Especially I would invite attention to the cause of the 

 remedial influence of pressure, as auxiliary to other means of cure. 



Recapitulation. 1st. Substances formed of organic matter are 

 generally penetrable by gases of all kinds, and by several, if not by 

 all liquids. 



2d. Each animal or vegetable tissue is differently penetrable as to 

 time by different fluids. 



3d. But all fluids penetrate any particular substance at rates sus- 

 ceptible of being ascertained. The gases retain the relation observed 

 by reference to one substance in all other cases. Whatever may be 

 the greater or less penetrability of any given tissue, the gases pene- 

 trate it, relatively to each other, according to the ratio observed in 

 experiments on other tissues. 



4th. The ratio is not so uniform in the instance of denser fluids. 

 Liquids, though rateable with regard to permeation of any given 

 substance, do not act similarly on different organic substances. Thus 

 water penetrates most, if not all animal tissues, better.tiiaiii any other 

 liquid whatever, and consequently passes through* thfcm/ to accumu- 

 late in any of its own solutions, and in alcohol or ether; while these 

 two latter substances penetrate gtwnelastic with more facility than 

 either water or its solutions. Therefore, with regard to gases, the 

 ratio of penetration depends on them alone ; while, in the case of 

 liquids, it depends on the joint agency of both liquids and tissues. 

 5th. When the quantity of the fluids is limited, there is a gradu- 



"North Amer. Med. and Surg. Jourii. No. VI. 1827. 



