FACTORS INFLUENCING BODY TEMPERATUKE 51 



but this is too slow and too limited to permit either to 

 maintain a constant temperature as a homoiotherm does. 

 The ability of fishes to adjust themselves to temperature 

 changes depends on the type of environment in which 

 they have previously lived (Hathaway, 1927, 1928). 

 Overheating of an animaPs body may result in acidosis 

 and death (Barbour, 1921). An animal may exercise to 

 produce heat if its body becomes too cool. Bees flap their 

 wings when their hive becomes too cool ; a mammal shiv- 

 ers when chilly. In mammals the chemical production 

 of heat becomes important only when the temperature 

 of the environment is as low as 14 to 15 deg. C. (Barbour, 

 1921; Britton, 1922). 



Glandular secretions are potent factors in regulating 

 metabolism and body temperature in vertebrates. In 

 pigeons the thyroid grows larger in autumn, when there 

 is an increase in heat production (Riddle, 1925; Riddle 

 and Fisher, 1925). Less thyroid secretion is apparently 

 needed by tropical animals than by those in cooler 

 regions (Sundstroem, 1922). Glandular secretions, such 

 as epinephrin and thyroidin, may affect body tempera- 

 tures by changing the water balance in an animal's body 

 (Barbour, 1921). The blood of an animal in an ice bath 

 becomes concentrated (Barbour and Tolstoi, 1921), and 

 is more dilute when the temperature is high (Barbour, 

 1921). In the tropics mammals have relatively fewer 

 white and more red blood corpuscles (Sunstroem, 1922). 

 Greater concentration of the blood at lower temperatures 

 makes animals better able to endure suboptimum tem- 

 peratures and permits them to remain active. Among 

 aquatic poikilotherms the character of the water sur- 

 rounding the body may influence the rate of metabolism, 

 and heat production. For example, a planarian shows 

 a considerable increase in respiratory activity in alkaline 



