GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 861 



the most active manifestations of vital power; and it is in these two pro- 

 cesses conjointly, not in either alone, that the function of Respiration essen- 

 tially consists. We shall now inquire into the sources from which Carbonic 

 acid is produced in the living body, and the causes of the demand for Oxy- 

 gen. 



280. The vital activity of the organism at large involves a continual 

 change in its constituent parts; and those which (so to speak) live the fast- 

 est, usually die the soonest, and pass most readily into decay (chap, x, sect. 

 1). Hence in the very performance of the Organic functions which concur 

 to effect the Nutrition of the body, there is a constant source of disintegra- 

 tion ; and one of the chief products of the decay of the tissues, which is 

 consequent upon their loss of vitality, is Carbonic acid. Thus the vioxt 

 general object of the Respiratory process, which is common to all forms of 

 organized being, is the extrication of this product from the system ; and the 

 demand for aeration hence arising, will vary with the activity of the nutri- 

 tive operations. Now the rate of life, and consequently the amount of dis- 

 integration, in any organized structure, depend in great measure upon the 

 temperature at which it is maintained ; and thus it happens that the produc- 

 tion of Carbonic acid from this source, at the ordinary rate of vital activity, 

 is much more rapid in " warm-blooded " than in " cold-blooded " animals, 

 and that the former suffer far more speedily than the latter from the priva- 

 tion of air. But when the temperature of the Reptile is raised by external 

 heat to the level of that of the Mammal, its need for respiration increases, 

 owing to the augmented waste of its tissues. When, on the other hand, the 

 warm-blooded Mammal is reduced, in the state of hibernation, to the level 

 of the cold-blooded Reptile, the waste of its tissues diminishes to such an 

 extent, as to require but a very small exertion of the respiratory process to 

 get rid of the carbonic acid, which is one of its chief products. And in 

 those animals which are capable of retaining their vitality when they are 

 frozen, or when their tissues are completely dried up, vital activity and dis- 

 integration are alike entirely suspended, and consequently there is no Car- 

 bonic acid to be set free. 



281. But another source of Carbonic acid to be set free by the Respiratory 

 process, and one which is peculiar to animals, consists in the rapid changes 

 which take place in the Muscular and Nervous tissues, in the very act of per- 

 forming their peculiar functions; the development of the Muscular and of the 

 Nervous forces involving, as the very condition of their production, a change 

 in the substance of these tissues respectively ; in which change a large quantity 

 of Oxygen is consumed, and a large amount of Carbonic acid is generated. 

 Hence in Man, as in all Animals, in which the Nervo-Muscular apparatus 

 constitutes the essential part of the organism, a powerful demand for Respi- 

 ration is created by its activity ; the amount of oxygen taken in, and of Car- 

 bonic acid exhaled, being determined, cceteris paribus, by the degree in which 

 this apparatus is exercised. That Carbonic acid is set free ready formed by 

 the muscles, and is not exclusively generated by the oxidation of the prod- 

 ucts of their disintegration after the reception of these into the blood-current, 

 has been shown by the experiments of Dr. G. Liebig, 1 who found that care- 

 fully prepared frogs' muscles absorb Oxygen and exhale Carbonic acid so 

 long as their contractility lasts, even when they have been completely de- 

 prived of blood. 2 In the similar experiments more recently made by M. 



1 Bericht d. Akad. d. Wissensch. zu Berlin, 1850, \\ 339-347. 



2 The statement of MM. E<tor and St. Pierre, that the formation of carbonic acid 

 is most energetic in the arterial system ( Robin's Journal de 1'Anatomie, 1865, p. 302), 

 has been refuted by Hirschman (Du Bois-Eeymond's Archiv, 1866, p. 502), and 

 Hoppe-Seyler (Med. Chem. Untersuch, Berlin,'l867, p. 295). 



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