422 



AN AMERICAN TEXT- IK >< >K OF PHYSIOLOGY. 



tension "I' 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 () and CO a through the skin, than by ligature of the trachea; 

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

 Dearly the same quantities of O are absorbed and C0 2 eliminated after the 

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

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



The quantity of CO., 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 C0 2 eliminated, 1 : 200-250. 



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

 affect the interchange in the luugs, 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 C0 2 resulting from 

 ti->ue-activitv. The organism may be regarded as an aggregation of living 

 cells, each of which during life consumes O and gives off CO z . 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. Quinquaud 1 records 

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

 three hours to a temperature of 38° : 



Muscle 23 c.c. 



I hart 21 " 



Brain 12 " 



Liver 10 " 



Kidney 10 " 



Spleen 8 



Lungs 7.2 



Adipose tissue 6 



Bone 5 



Blood 0.8 



The quantity of ('()_, formed in each case was approximately proportional to 

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

 low. The blood is not merely a carrier of O aud C0 2 to and from the tissues, 

 but is itself th'' -eat of active disintegrations which involve the consumption 

 of O and the production of C0 2 and other effete matters. Ludwig and his 

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

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

 lung- or other living tissues, more < > is consumed and C0 2 given off than by 

 1 Complet rendua de /« Societe de biohgu (9), 1890, 2, pp. 29, 30. 



