266 FUNCTIONS OF NUTRITION. 



Cooling of the Blood in the Lungs and Skin. While in the other 

 internal organs the blood is warmed during its passage through the 

 capillary vessels, in the lungs its temperature is slightly diminished. 

 This fact, which has been alternately asserted and denied, owing to the 

 difficulty of excluding incidental causes of error, has been abundantly 

 confirmed by the observations of Hering, Bernard, Heidenhain and 

 Korner, and Strieker and Albert. That of Hering was made on a young 

 calf, otherwise in good condition, but having the malformation of ectopia 

 cordis, so that the heart was unaffected by the contact of other organs. 

 In this case the blood of the right ventricle had a temperature of 39.37, 

 that of the left ventricle 38.15. Heidenhain and Korner,* in 94 obser- 

 vations on the dog, partly with thermo-electric needles and partly with 

 the mercurial thermometer, found the temperature of the blood equal on 

 the two sides of the heart in only one instance. In all the others, it 

 was higher on the right side than on the left, by 0.1 to 0.6. Ber- 

 nard,! who first demonstrated this difference by the mercurial 

 thermometer, has shown it also by the use of thermo-electric needles, 

 introduced into the right and left ventricles of the dog's heart, through 

 the jugular vein and carotid artery respectively ; always finding the 

 blood in the right ventricle warmer than that in the left. According 

 to these observations, the difference in temperature may amount in the 

 fasting animal to 0.174, during digestion to 0.232. Although during 

 digestion the temperature of the blood generally is higher than in the 

 fasting condition, the difference between the two sides of the heart 

 continues to show itself in the same direction. 



The diminution in temperature of the blood while passing through 

 the lungs is usually attributed to the cooling influence of the air in 

 the pulmonary cavities and to the vaporization of watery fluid. As 

 the air expelled by respiration is warmer than when introduced into 

 the lungs, it must withdraw a certain amount of heat from the internal 

 parts ; and as it contains watery vapor disengaged from the lungs, the 

 vaporization of this fluid must also reduce the temperature of the 

 organs. Whether these causes are more or less than sufficient to account 

 for the difference in the blood on the two sides of the heart has not been 

 determined. It is possible that a certain amount of heat is produced in 

 the lungs, as in other internal organs ; and that the heat so produced is 

 more than counterbalanced by that lost from the pulmonary surface, -the 

 total effect on the blood being consequently a lowering of its temper- 

 ature. In the cutaneous circulation similar causes exist for a cooling 

 effect on the blood; namely, the contact of the air, and the vapori- 

 zation of watery fluid supplied by perspiration. It is for this reason 

 that the superficial parts of the body are less warm than the interior ; 

 and accordingly the blood, after passing through the vessels of the integ- 

 ument, returns to the centre with its temperature slightly diminished. 



*Archiv fur die gesammte Physiologic. Bonn, 1871, Band iv., p. 558. 

 t Revue Scientifique. Paris, 1871, No. 1, p. 946. 



