86 ANN HAVEN MORGAN 



on the ground that immersion of the larger areas heated the blood, 

 which in turn warmed the spinal cord and reduced its irritabihty. 

 With the stimulation of the small area no such general warming 

 could take place, and hence the normal irritability of the cord 

 was retained and the vigorous response followed. 



Certain puzzhng phases immediately presented themselves, 

 and Sedgwick ('82) repeated the experiments upon which this 

 explanation was based. He suspended the reflex frogs in the 

 manner described by Foster and at once discovered that in this 

 upright position the heart was practically empty and could not 

 possibly circulate the blood as stated by Foster. 



From this tangle of statements the best e\ddence seems to 

 show that the reflex frog will respond to heat at certain degrees, 

 no matter how gradually it is appKed, but that the extent and 

 vigor of these responses may be reduced by the graded application 

 of the stimulus. 



Effect of heating and cooling the spinal cord. With the object 

 of stimulating the spinal cord, Archangelsky ('73) suspended 

 reflex frogs with their trunks surrounded by a jacket of hot air 

 which produced a rise of excitability, and by a jacket of slowly 

 heated air which produced no change. Tarchanow ('71, '72) 

 stimulated the cord directly with an ice pack, thereby causing a 

 depression of reflexes. 



Frogs can withstand a temperature as low as 6°C. The body 

 temperature of frogs was recorded by Milne-Edwards ('68) and 

 by Rogers and Lewis in 1916. Knauthe ('91) and Miiller- 

 Erzback ('91) froze frogs in water and exposed them to tempera- 

 tures of — 4°C. to — 6°C. for several hours. Maurel et Lagriffe 

 ('00) studied the effect of temperatures from -4°C. to 41°C. 

 and maintained that a frog may survive a temperature of 0°C. or 

 even -3°C. 



Respiration is quickened under stimulation by heat. "^^Tien 

 Babak ('13) warmed the skin of a reflex frog, the speed of respira- 

 tory movements was quickened, and when he cooled it, corre- 

 spondingly the speed was decreased. 



Frogs which are immersed in cold water will swim downward and 

 will remain at the bottom a greater percentage of the time as the cold 



