§ 5.111 RESPIRATION 175 



have been recorded for several amphibia (as well as for some fish 

 and lizards) living in temperate climates (Lynn and Wachowski, 

 1951). It would seem as if the increase in thyroid activity in the 

 summer enables these cold-blooded species to attain a high enough 

 rate of basal metabolism even in temperate climes to become 

 active despite the relatively low and variable temperature. 



Fig. 5-3. Percentage changes in oxygen consumption of the rat, 

 Rattus, (ordinates) with time in days (abscissae) when thyroid 

 EXTRACTS are injected intra-peritoneally. There is little difference 

 in effect between injection of 100 mg mammalian thyroid powder 

 (black circles) and of 95 mg dogfish, Scyliorhinus, thyroid (white 

 circles). Both cause considerable increase for about a week as 

 compared with either normal controls (white triangles) or even 

 controls injected with 2-0 ml 0-9% NaCl (black triangles). (From 

 Matty, 1954). 



Increase in oxygen consumption due to thyroxine is never 

 very great in Amphibia. Tadpoles and axolotls seem to be more 

 responsive than adult frogs to thyroid treatment, whether this is 

 given by feeding or injection. Thyroidectomy might make the 

 frogs more sensitive, especially if they were tested in the winter 

 with amphibian rather than mammalian thyroid extracts. The fact 



