MODE OF PRODUCTION OF ANIMAL HEAT. 309 



eorclis, by which the heart was withdrawn from the immediate contact 

 of other organs, and in which case the blood of the right ventricle had 

 a temperature of 39.37, that of the left ventricle 38.75. Heidenhain 

 and Korner, 1 in 94 observations on the dog, partly with the use of thermo- 

 electric needles and partly with the mercurial thermometer, found the 

 temperature of the blood on the two sides of the heart equal 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. Bernard, 2 who first demonstrated this differ- 

 ence 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 physical influence of the cooler air in 

 the pulmonary cavities and to that of 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, furthermore, watery vapor disengaged from the 

 lungs, the vaporization of this fluid must also reduce the temperature of 

 the respiratory organs. Whether the cooling influence of these causes 

 is more or less than sufficient to account fully for the difference in the 

 blood on the two sides of the heart has not been determined. It is pos- 

 sible that heat is also produced in the lungs, as in the other internal 

 organs ; but that the w r hole of it, and a little more, is consumed by the 

 influence of the air upon the pulmonary membrane. It is evident, how- 

 ever, that physical conditions exist in the lungs which must cause the 

 disappearance of more or less sensible heat ; and it is certain that the 

 blood, in point of fact, diminishes slightly in temperature while passing 

 through the pulmonary circulation. 



In the cutaneous circulation the same physical causes exist for a cool- 

 ing effect on the blood as in the lungs ; namely, the contact of the skin 

 with the cooler air, and the vaporization of the watery fluid supplied by 

 perspiration. It is for this reason, as already mentioned, that the super- 

 ficial parts of the body have a normal temperature somewhat below that 

 of the interior ; and accordingly the blood, after passing through the 

 vessels of the integument, returns to the centre with its temperature 

 slightly diminished. There is every reason to believe that the tissues 

 of the skin and subjacent parts evolve a certain amount of heat by their 

 own nutritive changes ; but the heat thus produced, as in the case of the 



1 Archiv fur die Gesammte Physiologie. Bonn, 1871, Band iv. p. 558. 



2 Eevue Scientifique. Paris, 1871, No. 1, p. 946. 



