RELATIONS OF RESPIRATION TO NUTRITION. 163 



We cannot stop at this point. Now it is known that the organic principles of the 

 body, which form the basis of all tissues and organs, are continually undergoing change 

 as a condition of existence ; that they do not unite with any substance in definite chemi- 

 cal proportions, but that their particles, after a certain period of existence, degenerate 

 into excrementitious substances and are regenerated by an appropriation and change of 

 materials furnished by the blood. As far as the respiration of these parts is concerned, 

 we can only say, that, in this process, carbonic acid is produced and oxygen is consumed. 

 These facts show that respiration is essentially a phenomenon of nutrition, possessing a 

 degree of complexity certainly equal to that of the other nutritive processes. It must 

 be acknowledged that thus far its cause and intimate nature have eluded investigation. 

 In respiration by the tissues, no one has yet been able to give the cause of the absorption 

 of oxygen or the exhalation of carbonic acid, or to demonstrate the condition in which 

 oxygen exists when once appropriated, or the particular changes which take place and 

 the principles which are lost, in the formation of carbonic acid. 



The views of physiologists with regard to the essential processes of respiration, be- 

 fore the time of Lavoisier, have barely an historical interest at the present day, except 

 the remarkable idea of Mayow, which comprehended nearly the whole process and 

 which was unnoticed for about a hundred years. It is not our object to dwell upon the 

 various theories which have been advanced from time to time, or even to fully discuss, in 

 this connection, the combustion-theory as proposed by Lavoisier and modified by Liebig 

 and others. Although this theory is nominally received by many physiologists of the pres- 

 ent day, it will be found that most of them, in accordance with the facts which have 

 since been developed, really regard respiration as connected with nutrition. They only 

 differ from those who reject the combustion-theory, in their definition of the term com- 

 bustion. Lavoisier regarded respiration as a slow combustion of carbon and hydrogen ; 

 and, if every rapid or slow combination of oxygen with any other body be considered a 

 combustion, this view is absolutely correct and was proven when it was shown that 

 oxygen united with any of the tissues. Longet says that since the time of Lavoisier it is 

 agreed to give the above signification to the word combustion; but this must simply be 

 for the purpose of retaining the name applied by Lavoisier to the respiratory process, 

 while its signification is altered to suit the facts which have since taken their place in 

 science. There is no doubt that combustion is generally regarded as signifying the direct 

 and active union of oxygen with certain principles which commonly contain carbon and 

 hydrogen; and the immediate products of this union are carbonic acid, water, and, inci- 

 dentally, heat and light. It is certain that oxygen does not unite in the body directly 

 with carbon and hydrogen, although it is consumed and carbonic acid and water are pro- 

 duced in respiration. Important intermediate phenomena take place, and we do not 

 therefore fully express the respiratory process by the term combustion. The researches 

 of Spallanzani, W. F. Edwards, Collard de Martigny, and others, who have demonstrated 

 the abundant exhalation of carbonic acid by animals and by tissues deprived of oxygen, 

 show that it is not a product of combustion of any of the principles of the organism. 

 Rejecting this hypothesis as insufficient to explain the intimate nature of the respira- 

 tory process, it remains to be seen how satisfactorily, in the present state of the science, 

 it is possible to answer the several questions we have proposed. 



1. In what way is the oxygen consumed in the system? Oxygen taken from the air 

 is immediately absorbed by, and enters into the composition of the red corpuscles. Part 

 of the oxygen disappears in the red corpuscles themselves, and carbonic acid is given 

 off. To how great an extent this takes place it is impossible to say ; but it is evident, 

 even from a study of the methods of analysis of the blood for gases, that the property 

 of absorbing oxygen and giving off carbonic acid, which Spallanzani demonstrated to 

 belong to the tissues, is possessed as well by the red corpuscles. During life it is not 

 possible to determine how far this takes place in the blood and how far in the tissues. 

 The theory has been proposed that all the respiratory change takes place in the blood as 



