ANIMAL HEAT. 



483 



mous animals; it varies materially in intensity in different species, especially in 

 warm-blooded animals; and it is closely related to the intensity of respiration. 

 Moreover, it is probable that each species, and even each individual of the 

 species, has its own specific thermogenic coefficient, that is, a mean standard of 

 heat-production for each kilogram of body-weight or for each square centime- 

 ter of body-surface. The following figures giving the heat-production per 

 kilogram per hour, compiled by Munk, 1 are of interest both as regards species 

 and size and weight of the animal in relation to heat-production : 



Horse 1.3 kilogramdegrees. 



Man 1.5 " 



Child (7 kilograms) . . 3.2 " 



Dog (30 " ) . . 1.7 " 



Dog (3 " ) . . 3.8 " 



Guinea-pig 7.5 " 



Duck 6.0 kilogramdegrees. 



Pigeon 10.1 " 



Rat 11.3 " 



Mouse 19.0 " 



Sparrow 35.5 " 



Greenfinch 35.7 " 



These figures have an additional interest when compared with the respira- 

 tory activity of different species (p. 429). The intensity of respiration has a 

 marked significance both in connection with the species and the individual. 

 The larger the quantity of oxygen consumed the greater relatively is the 

 activity of oxidation processes, and, consequently, the more active is heat-pro- 

 duction (see p. 429). Therefore, all circumstances which affect respiratory 

 activity tend to affect thermogenesis. The intensity of respiratory activity and 

 the extent of body-surface in relation to body-weight are closelv related (p. 

 430). 



Increased activity of the circulation is favorable to increased heat-produc- 

 tion, this being due to several factors: (1) A more abundant supply of blood 

 may be accompanied by increased metabolic activity. (2) Increased circulatory 

 activity is favorable to increased heat-dissipation by causing a larger supply 

 of blood to the skin, thus facilitating loss by radiation and indirectly tending to 

 increase thermogenesis. (3) Increased circulatory activity also excites the respi- 

 ratory movements and the secretion of sweat, thus increasing heat-loss and in- 

 directly favoring heat-production. (4) The more active the circulation the 

 larger the amount of heat produced by the heart and the movement of the 

 blood. The diurnal fluctuations of the pulse-rate are said to be more or less 

 closely related to similar changes of body temperature. 



Arise of internal temperature (body temperature) is favorable to increased 

 metabolic activity (p. 432) and, therefore, to an increase of heat-production ; 

 conversely, a fall of body temperature tends to reduce heat-production. The 

 influences of body temperature are, as a whole, less important than those of 

 external temperature. 



The influences of external temperature axe in a measure differenl upon homo- 



thermous and poikilothermous animals. In the former, heat-production is in 



inverse relation to the temperature of the surrounding medium, so that the 



cooler the ambient temperature the greater the heat-production ; in the latter 



1 Physiologie dea Menachen und der Sdugethiere, L892, 8. 302. 



