THEORY. 389 



capillaries. When we fully consider the differences exhibited in 

 the blood before and after the absorption of the oxygen in the 

 lungs (see vol. ii., pp. 248 and 259), we shall find some diffi- 

 culty in yielding to the opinion, that the parenchyma of vitally 

 active organs is the only destination of the oxygen. 



We will simply remark in conclusion, that the very decisive 

 influence of the different nutrient substances on the process of 

 respiration, which we have shown to exist, cannot be recon- 

 ciled with the view, that all oxidation must take place in the 

 parenchyma of the organs. The carbo-hydrates, as well as the 

 excess of albuminates, are very quickly oxidised, as might be 

 conjectured, from the pulmonary and urinary excretion; these 

 substances, which are absorbed in what may be termed superfluous 

 consumption, are not first converted into constituents of the 

 organs to be again excreted ; but whether they are first conveyed 

 from the blood and carried into the innermost parts of the organs 

 in order to be consumed, is a question which we are not yet able 

 to decide ; there seems at the present day to be every appearance 

 of probability that the greater part of the carbo-hydrates and fats, 

 and the excess of albuminates, are decomposed and oxidised 

 within the course of the blood. 



Now that we have convinced ourselves, in the course of our 

 inquiries, that that interchange of oxygen and carbonic acid, which 

 we term respiration, is a process which is not limited to any 

 individual part of the animal body ; and now that we have seen 

 how, on the one hand, an interchange of air is effected in the air- 

 passages by the double means of mechanical transport and by 

 diffusion, and how, on the other hand, an active interchange of 

 gases takes place in the parenchyma of all the organs and in their 

 capillaries, it simply remains for us to ascertain the laws which 

 control the interchange between the elastic gases of the air con- 

 veyed to the lungs and the condensed gases of the blood of the 

 pulmonary capillaries upon the humid mucous membrane of the 

 pulmonary vesicles. 



We shall wholly pass over the older theories regarding the 

 process of respiration, as they were almost exclusively mere 

 hypotheses based on few facts, and consequently not explanations 

 considered in a scientific point of view ; nor, indeed, were such 

 explanations possible at that time, when scarcely a conjecture had 

 been hazarded in reference to the laws of absorption, of diffusion, 

 and many other physical principles bearing upon this subject. 

 Although we can scarcely yet venture to hope that we are 



