Mitchell on the Penetrativeness of Fluids. 



exhaust us; for it not only acts upon excitability, but creates a fresh 

 supply of it, so that its consumption is not felt. We can also easily 

 see why an animal was destroyed in ten minutes by breathing 1 hydro- 

 gen, while carbonic acid produced the same effect in two minutes. 

 In Section I. Article IX. of his Physiological Researches, Bichat 

 relates some curious exemplifications of the passage of gases into the 

 blood-vessels through the lungs of living animals. For instance, 

 hydrogen gas could be set on fire, as in bubbles it escaped from a 

 remotely situated blood-vessel. As he had used some force, by means 

 of a stop-cock and syringe adapted to the trachea, to throw in and 

 retain the gas, he ascribes its entrance to that cause. We see how- 

 ever that though impulsion augments the effect, yet that it is existent 

 independently of any vis a tergo. Gases not at all soluble in blood, 

 will not pass without force, but that force is, in some degree, applied 

 in every act of expiration. Those soluble in blood find ready en- 

 trance when not held back by the interstitial molecular power of the 

 other gases with which they enter the bronchiae. 



The emptiness of the blood-vessels after death, or rather their 

 fulness of gaseous matter, is no longer a case of difficult solution. 

 Always present in the air-cells after death, air and carbonic acid gas 

 must find a ready entrance into the emptied capillaries of the lungs, 

 always prompt to dilate through the influence of the elastic matter 

 which exists in and around them in the lungs. As any kind of air 

 acts as a stimulant to the heart's cavities *, a gaseous circulation is 

 kept up, and the aeriform matter passes into the great channels of 

 circulation. 



It does not appear difficult to understand why so penetrating and 

 poisonous a gas as sulphuretted hydrogen should often exist in the 

 intestines without injury ; for, being mixed up with other gases, its 

 tendency to infiltration is greatly restrained. When undiluted, its 

 diffusion through the whole system is fearfully rapid. 



* Of all the gases/ says Dr. Ure, * sulphuretted hydrogen is the 

 most deleterious to animal life. A greenfinch plunged into air which 



* In 1823, being engaged in dissecting a sturgeon, (Acipenser brevirostrum?) 

 its heart was taken out and laid on the ground, and after a time, having ceased to 

 beat, was inflated by mouth for the purpose of drying it. Hung up in this state it 

 began again to move, and continued for ten hours to pulsate regularly, though more 

 and more slowly. Left at 1 A. M. in slow motion, it was found next morning still 

 and hard. When last observed in motion, the auricles had become so dry as to 

 rustle as they contracted and dilated. 



With the heart of a Testudo serpentaria, (Snapper,) I lately repeated the 

 experiment, and found it beat well under the influence of oxygen, hydrogen, car- 

 bonic acid, and nitrogen, successively thrown into it. Water also stimulated it 

 perhaps more strongly, but made its substance look pale and hydropic, and in one 

 minute destroyed action beyond all known means of restoration. 



