390 COMPARATIVE PHYSIOLOGY. 



salts, as sodium bicarbonate, but that the corpuscles in some way 

 determine its relations of association and disassociation. Some 

 think a good deal of this gas is actually united with the red cor- 

 puscles. 



We may now inquire into the more intimate nature of respi- 

 ration in the blood. From the facts we have stated it is obvious 

 that respiration can not be wholly explained by the Henry-Dal- 

 ton law of pressures or any other physical law. It is also plain 

 that any explanation which leaves out the principle of pressure 

 must be incomplete. 



While there is in oxy-hsemoglobin a certain quantity of 

 oxygen, which is intra-molecular and incapable of removal by 

 reduction of pressure, there is also a portion which is subject 

 to this law, though in a peculiar way ; nor is the question of 

 temperature to be excluded, for experiment shows that less 

 oxygen is taken up by blood at a high than at a low tempera- 

 ture. 



We have learned that in ordinary respiration, the propor- 

 tion of carbonic dioxide and oxygen in different parts of the 

 respiratory tract must vary greatly ; the air of necessity being 

 much less pure in the alveoli than in the larger bronchi. 



It is customary to speak of the oxygen of oxy-hffimoglobin 

 as being in a state of " loose chemical combination." The en- 

 tire truth seems to lie in neither view, though both are partially 

 correct. The view entertained by some physiologists, to the 

 effect that diffusion explains the whole matter, so far, at least, 

 as carbonic anhydride is concerned, and that the epithelial cells 

 of the lung have no share in the re~spiratory process, does not 

 seem to be in harmony either with the facts of respiration or 

 with the laws of biology in general. Why not say at once that 

 the facts of respiration show that, here as in other parts of the 

 economy, while physical and chemical laws, as we know them, 

 stand related to the vital processes, yet, by reason of being vital 

 processes, we can not explain them according to the theories of 

 either physics or chemistry ? Surely this very subject shows 

 that neither chemistry nor physics is at present adequate to 

 explain such processes. It is, of course, of value to know the 

 circumstances of tension, temperature, etc., under which respi- 

 ration takes place. We, however, maintain that these are con- 

 ditions only — essential no doubt, but though "important, that 

 they do not make up the process of respiration. But, because 

 we do not know the real explanation, let us not exalt a few 



