EFFECTS OF RESPIRATION ON THE BLOOD. 407 



543. The aeration of the blood may take place, not only by means of the 

 lungs, but also through the medium of the cutaneous surface. In some of the 

 lower tribes of animals, indeed, this is a very important part of their respira- 

 tory process ; and even in some Vertebrata, the cutaneous respiration is capa- 

 ble of supporting life for a considerable time. This is especially the case in 

 the Batrachia, whose skin is soft, thin, and moist ; and the effect is here the 

 greater, since the blood which circulates through the system is, from the small 

 proportion of it that has passed through the lungs, very imperfectly arterial- 

 ized. By the experiments of Bischoff it was ascertained that, even after the 

 lungs of a Frog had been removed, a quarter of a cubic inch of carbonic acid 

 was exhaled from the skin, during eight hours. Experiments which have 

 been made on the Human subject leave no room for doubt, that a similar pro- 

 cess is effected through the medium of his general surface ; for, when a limb 

 has been enclosed for some hours in an air-tight vessel containing atmospheric 

 air freed from carbonic acid, a sensible amount of this gas has been found to 



of iron in the blond-corpuscles, as they pass alternately through the systemic and the 

 pulmonary capillaries. His chief facts' are 1. That the elementary composition of the 

 colouring matter is the same, whether obtained from arterial or from venous blood, viz., 

 C. 44, H. 44, N. 6, O. 6, Fe. 2. That the change from dark to bright blood is effected as 

 completely by the agency of a neutral salt as by oxygen. 3. That if the iron were present 

 in the blood as an oxyde (and especially as a peroxyde), it should be easily extracted by 

 weak acids; but he has found that well-prepared hsamatine may be digested in diluted 

 hydrochloric or sulphuric acid for several days without the iron in it being in the least 

 diminished. After being so treated, he has obtained, after incineration, the regular pro- 

 portion of 9-49 per cent, of oxyde.* If strong sulphuric acid be poured on dried blood, 

 or dried pure haematine,and kept on it for some days, and then water be added, hydrogen 

 is evolved, and sulphate of peroxyde of iron is found in the solution, which could not 

 happen if the iron had been at first in the form of peroxyde.j- 5. The iron may thus 

 be all extracted from the blood, or from haematine, (though not, as some say, without 

 affecting the colour,) and the other constituents may be obtained in a separate form. 

 Numerous analyses of this constituent, by Van Goudoever, regularly yielded the same 

 equivalents of the elements, viz., C. 44, H. 44, N. 6, O. 6; but if the iron had been united 

 with this in the form of Fe. 2, O. 3, and in the proportion of one equivalent to two, there 

 should have remained only four and a half equivalents of oxygen. 



Mulder concludes, therefore, that iron is present in hsematine, as iodine is in sponge, 

 or sulphur in cystine, or arsenic in cacodyl. His notion of the mode in which the changes 

 of colour are effected is, that when the corpuscles of the venous blood are exposed in the 

 lungs, oxy-proteine is formed by the oxydation of the fibrin proteine of the liquor san- 

 guinis, or perhaps, by the oxydation of the outer layer of the cell membrane of the 

 corpuscles. If formed in the liquor sanguinis, its peculiar plasticity would lead to its 

 being deposited in a thin layer on the corpuscles. In either such case, the dark corpus- 

 cles would, after respiration, be invested by a thin layer of white and imperfectly trans- 

 parent oxy-proteine, or buffy coat, through which they would look bright-red, as dark 

 blood does when contained in a vessel of milk-white glass. But, in the systemic capil- 

 laries, the oxy-proteine may be consumed in nutrition, and the darkness of the corpuscles 

 will then again appear unveiled. 



Moreover, since it appears that, in the biconcave form, the corpuscles, by reflecting 

 more light, are always bright, and in the biconvex form always dark, it may be that in 

 the arterial blood they are not only buffed, but also cupped, by the oxy-proteine, by the 

 plastic properties of which, moreover, it is easy, on this pretty theory, to explain the 

 ready adhesion of the corpuscles in inflammatory blood. Diluted acids, which make 

 bright blood dark, may do so by making the outer layer of the corpuscles transparent, as 

 they do fibrin before dissolving it; and concentrated solutions of neutral salts may 

 make it bright by making the same layer contract. M. C.] 



* [Liebig adduces the possibility of extracting iron from dried blood as one of the proofs 

 of its being in an oxydized state; but Mulder says this iron must have been extracted 

 from some other constituent of the blood; for others, besides the globules, even pure 

 serum, contain iron.] 



f [When the blood or its colouring matter has been exposed to the air prepared in it, 

 the iron must always, according to Liebig's view, be in the state in which he supposed 

 it to be in arterial blood.] 



