310 Mitchell on the Penetrativeness of Fluids. 



stances dart with surprising facility, losing as their particles sepa- 

 rate, all cohesion, and acting repulsively. The oils are remarkable 

 in this regard, and camphor exhibits, because of it, curious and 

 agreeable movements, when thrown upon perfectly clean water*. 



But it is chiefly with reference to physiology, pathology, and 

 practical medicine, that we see, in the foregoing experiments, things 

 of much real value. They throw a particular light on the functions 

 of respiration and cuticular absorption, and will probably lead to 

 the employment of gaseous agents of cure with confidence and 

 certainty. 



The experiments on the mutual action of gases and liquids, show 

 that although a gas may, when alone presented to a liquid for which 

 it has no chemical affinity, penetrate its molecular cavities, yet, it 

 will again leave it to join any gas whatever, which is brought into 

 communication with the liquid. Thus carbonic acid or nitrous 

 oxide readily penetrates blood or water, but returns from either into 

 the air or any other gaseous substance, which contains no carbonic 

 acid, or nitrous oxide. It is in this way, probably, that the oxygen 

 disappears, and an exactly equal quantity of carbonic acid replaces 

 it in the bronchial cells. Oxygen penetrates slowly the membra- 

 nous tissue, to infiltrate and brighten the blood; carbonic acid is 

 immediately formed, and being a gas differing from the remainder 

 of the air yet in the air-cells, its tendency is to return, to penetrate 

 that air, and thus escapes through the trachea along with it. The 

 oxygen enters, because there is oxygen enough behind to permit 

 that, and it is also an observed fact. The carbonic acid formed, 

 makes its escape, because invited by the molecular tissue of atmo- 

 spheric air. Keeping up any reference to known facts, we can 

 scarcely doubt the truth of our explanation, or venture to adopt any 

 other. The investigations of John Davy, and our careful repetition 



* The best mode of examining this property of camphor is the following : Take 

 a piece of cork, a flat four-sided prism, and attach to its narrow sides, close to the 

 ends, and diagonally opposite to each other, two small pieces of camphor. Resting 

 with its broad surface upon a considerable plane of quite clean water, the appara- 

 tus will regularly rotate, and that either until the camphor is consumed, or the 

 interspace is filled with that substance, or an emanation from it. Oil, by filling 

 the space, immediately suspends the motion. If a cork be greased slightly, or 

 camphorated at the end, it will move in a direction from that end, and with consi- 

 derable velocity. The same thing happens when fine dry flour is attached, or 

 when the butt end of the cork is dipped into ether or alcohol. A cavity being 

 made in the upper surface of a floating cork, near the end, filled with ether, and 

 connected by a cotton filament with the water, it will sail about a pneumatic trough 

 for a considerable time, always moving towards the solid end. A little rudder 

 being attached to the cork, and slightly inflected, the vessel may be made to sail 

 entirely round a circular tub. 



