2l6 NATURAL SCIENCE. March. 



It is interesting that Crawford and Lavoisier were the first to 

 make experiments on the amount of heat given off by animals, and 

 even to compare the oxidation, as represented chiefly by the carbonic 

 acid, with the amount of heat produced. They showed that the 

 oxidation could produce the necessary heat. 



John Davy in 18:5 showed by more exact experiments that there 

 was no perceptible difference in the specific heat of arterial and of 

 venous blood, and therefore Crawford's theory must fall to the 

 ground. This, however, by no means affected the doctrine of 

 Lavoisier, that the oxidation in the animal body was the cause of the 

 heat. In fact, Liebig not many years later, by properly interpreting 

 the calorimetric experiments of Baling and Despretz, placed 

 Lavoisier's doctrine on such a firm basis that it became strong 

 evidence for the Law of the Conservation of Energy. 



In the last fifty years the labours of Helmholtz, Ludwigand Pfliiger 

 have proved that the heat is formed in the tissues, that heat is produced 

 by the activity of muscles and glands. Bernard also, by showing 

 how variations of the circulation of the bood could be effected by the 

 nervous system, threw a great light upon tlie process of heat regula- 

 tion. The formation of heat varied in different parts, but the tem- 

 perature was equalised and regulated by the continual blood-stream ; 

 the circulation of the blood, being under the control of the nervous 

 system, could, when necessary, send more blood to the surface, and 

 so increase the loss of heat, at another time could husband the 

 warmth by diminishing the blood-supply to the skin. 



Such have been the chief lines along which the knowledge of the 

 causes of animal temperature has advanced. The doctrine of " vital 

 heat," propounded by the vitalistic school, has fallen before the 

 advance of materialism ; " vital heat " is shown to be similar to heat 

 arising from physical and chemical processes. 



Numerous observations upon animal temperature have now 

 accumulated. Of these the most interesting, without doubt, lies 

 in the difference which has been found to exist between the 

 lower and the higher animals. Those animals which are high 

 in the scale of evolution, such as birds and mammals, have a 

 high temperature, and this has a mean value (about 37° C. or 98° 

 F. in man) which is independent of the temperature of the sur- 

 rounding air. The lower animals on the contrary, such as molluscs, 

 fishes, amphibians and reptiles, have a temperature generally only 

 slightly above that of their surroundings. This difference between 

 the two classes is expressed by the terms "warm-blooded" and 

 " cold-blooded " animals. 



The warm-blooded animal has in correspondence with its high 

 temperature a very energetic oxidation within its tissues, and this 

 must, caiens paribus, be more vigorous in the winter than in the 

 summer. The cold-blooded animals, on the contrary, have a much 

 smaller oxidation, and one which is so lessened by cold that in winter 



