ANIMAL HEAT. 509 



figures are the result of numerous experiments made upon dogs. The maximum of thirty- 

 three observations upon the temperature in the aorta was 105'8, and the minimum, 98-78; 

 the maximum of thirty-two observations upon the portal vein was 106'34, and the mini- 

 mum, 100'04 ; the maximum of thirty -five observations upon the hepatic veins was 107, 

 and the minimum, 99'86. Compared with the aorta, the temperature of the portal vein 

 was generally found to be higher (maximum of difference, 0'9) ; but, in a few instances 

 (five out of fifteen), it was a very little lower, which is explained by Bernard upon the sup- 

 position that the intestinal canal is not entirely removed from external modifying influ- 

 ences. These results show that the blood coming from the liver is warmer than in any 

 other part of the body. 



The general fact that the superficial parts are cooler than those less exposed to loss 

 of heat by evaporation does not demand extended discussion ; but, in a series of experi- 

 ments by Breschet and Becquerel, who were among the first to employ thermo-electric 

 apparatus in the study of animal heat, it was found that the cellular tissue was from 2'5 

 to 3-3 cooler than the muscles. This difference will be readily understood when we 

 consider the production of heat in the general system, and more especially in the highly- 

 organized parts. 



A most interesting question, in this connection, relates to the comparative tempera- 

 ture of the blood in the two sides of the heart. I}pon this point there have been several 

 conflicting observations, the results favoring two opposite theories of calorification. By 

 some it has been thought that the blood gains heat in passing through the lungs, and this 

 is explained by the theory of the direct union, in these organs, of oxygen with the 

 hydro-carbons. Others suppose that the blood is slightly refrigerated in the air-cells. 

 The questions here involved will be fully discussed in connection with the theories of 

 animal heat ; and we shall confine ourselves at present to a study of the experimental 

 facts. 



It is evident that, when the chest is opened, the external refrigerating influences 

 might act differently upon the two sides of the heart, particularly as the right ventricle 

 is much thinner than the left. It would not be improper, indeed, to exclude all observa- 

 tions made in this way, and to depend entirely upon experiments in which the physiological 

 conditions are not so palpably violated. Magendie and Bernard introduced delicate ther- 

 mometers into the two sides of the heart, through the vessels in the neck, without opening 

 the chest. These experiments were made upon a horse, and the right heart was always 

 found considerably warmer than the left. Hering introduced a thermometer into the cavi- 

 ties of the heart in a living calf affected with cardiac ectopia. The temperature of the 

 right side was 102'74, and the left side, 101 '79. Georg von Liebig illustrated one of 

 the sources of error in all examinations made after opening the chest, by filling the cavi- 

 ties of the heart of a dog with warm water, placing the organ in a water-bath, and bring- 

 ing the two sides to precisely the same temperature. After five minutes' exposure to the 

 air, the temperature in the right ventricle was sensibly lower than in the left, which 

 was undoubtedly due to the difference in the thickness of the ventricular walls. The 

 observations by Bernard himself upon dogs and sheep are very conclusive, as far as 

 these animals are concerned. In dogs he found a difference of from 0'1 to 0*2, 

 always in favor of the right side ; and the results in sheep were nearly the same. 

 These experiments are only indirectly applicable to the human subject; and if it be 

 proven that, in animals, the conditions vary with "the state of the skin, the digestive 

 apparatus, and the muscular system " (Colin), it is impossible, in the absence of positive 

 demonstration, to say what change in temperature, if any, takes place in the blood in its 

 passage through the lungs. The only reliable observations upon this point in man are 

 those made by Prof. Lombard, of Boston. Prof. Lombard used in his experiments a very 

 ingenious and delicate thermo-electric apparatus, capable of indicating a difference of 

 ?oVo f a degree cent. With this instrument, he was able to determine very slight varia- 

 tions in the temperature of the blood in the arterial system, by simply placing the con- 



