316 Mitchell on the Penetrativeness of Fluids. 



ally diminished rate of progression as the infiltration proceeds. It is 

 proportional to the state of dilution, and ceases when the substances 

 have become, on lioth sides of the membrane, of uniform condition, 

 unless some extrinsic power is then operative. 



6th. The power of the penetrativeness is very considerable, being 

 certainly superior to that of two, and possibly equal to more than 

 that of forty atmospheres. 



7th. Penetrativeness acts not only on organic tissues, but also on 

 gases and liquids, and with apparently equal power on all. For, 

 after permeating a membrane, the gas or liquid goes on into the 

 molecular tissue of the gas or liquid beyond, and no pressure which 

 the membrane can bear acts as a restraint on the progression. 



8th. Although of such high mechanical power, the penetration can 

 be, to a certain degree, affected by extrinsic agency. Thus pressure 

 or attraction will cause permeation, where it would not otherwise 

 take place, as when a single gas or liquid travels not only through, 

 but beyond a membrane, where there exists nothing to imbibe it, 

 which it would not do, unless subjected to propulsion. Electricity, 

 possessed of hydragogue powers, acts on water in a similar manner, 

 causing it to collect on either side of an animal membrane, at plea- 

 sure, although no other liquid is there to receive it. 



9th. The penetrativeness of gases for each other seems to vary in 

 velocity, but not in force. 



10th. Reference to the abovementioned laws and modifying 

 agencies enables us to explain many phenomena hitherto imperfectly 

 understood. We, by means of them, comprehend the uniform con- 

 stitution of mixed gases in any vessel, or in the atmosphere, not- 

 withstanding the greatest difference in specific gravity. It explains 

 the diffusion of odours, the nature and power of spontaneous evapo- 

 ration, and the probable nature and progression of caloric under 

 slow conduction. It affords us new views of the theory of respira- 

 tion, and accounts, in that process, for some well-ascertained facts, 

 for which there previously existed no adequate explanation. 



It shows us how emphysema and tympanitis may happen without 

 secretion of gases, or lesion of tissue, and how a spontaneous cure 

 may be produced. It leads to the probability of the existence of 

 gaseous matter of very various kinds in almost every part of the 

 animal frame, resident there molecularly, and not en masse, but 

 susceptible of being collected into mass in the great cavities or the 

 cells of the tissue, or the blood-vessels, by mechanical or electrical 

 influence, or the attractive interstitial agency of other masses of air. 



It teaches the important truth, that water is the great general 



