530 



AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



tension of aqueous vapor, and for atmospheric pressure, as well as attention to 

 the many details connected with gas-analysis. 



Cutaneous Respiration. In frogs the skin is a more important respi- 

 ratory organ than the lungs, as is illustrated by the fact that asphyxia is 

 more rapidly produced by dipping the animal in oil, and thus preventing the 

 interchange of O and CO 2 through the skin, than by ligature of the trachea ; 

 moreover, the investigations of Regnault and Reiset show that in these animals 

 nearly the same quantities of O are absorbed and CO 2 eliminated after the 

 lungs are excised as in the intact animal. In man the reverse is the case, the 

 cutaneous interchange being insignificant as compared with that in the lungs. 



The quantity of CO 2 exhaled through the skin during twenty-four hours 

 has been estimated by different observers from 2.23 grams to as much as 32.08 

 grams. Compared with pulmonary interchange, the ratio of O absorbed is 

 probably about 1 : 100-200, and of CO 2 eliminated, 1 : 200-250. 



Cutaneous respiration is, as a rule, subject to the same circumstances that 

 affect the interchange in the lungs, and is accomplished, moreover, in the same 

 way. In some instances, however, it is influenced in the opposite direction ; 

 for instance, it is increased by circumstances that hinder pulmonary respiration. 

 Cutaneous respiration is favored by moist skin, and Ronchi found that it was 

 increased by higher external temperature. 



Internal or Tissue-respiration. The main object of the respiratory mech- 

 anism is to supply the organism with O and to remove the CO 2 resulting from 

 tissue-activity. The organism may be regarded as an aggregation of living 

 cells, each of which during life consumes O and gives off CO 2 . Activity 

 depends essentially upon processes of oxidation ; consequently, not only is oxi- 

 dation necessary for existence, but the quantity of O absorbed must bear a direct 

 relation to the degree of activity. The avidity of the different tissues for O 

 varies greatly, and the differences are doubtless expressions, broadly speaking, 

 of the relative intensities of their respiratory processes. Quinqnaud l records 

 the following absorption-capacities of 100 grams of each tissue, submitted for 

 three hours to a temperature of 38 : 



Muscle 23 c.c. 



Heart 21 " 



Brain 12 " 



Liver 10 " 



Kidney 10 " 



Spleen 8 c.c. 



Lungs 7.2 " 



Adipose tissue 6 " 



Bone 5 " 



Blood . 0.8 " 



The quantity of CO 2 formed in each case was approximately proportional to 

 the quantity of O absorbed. The respiratory value of blood is doubtless too 

 low. The blood is not merely a carrier of O and CO 2 to and from the tissues, 

 but is itself the seat of active disintegrations which involve the consumption 

 of O and the production of CO 2 and other effete matters. Ludwig and his 

 pupils long ago showed that when readily-oxidizable substances, such as lactate 

 of sodium, are mixed with the blood, and the blood is transfused through the 

 lungs or other living tissues, more O is consumed and CO 2 given off than by 

 1 Comptes rendus de la Societe de biologic (9), 1890, 2, pp. 29, 30. 



