380 ANIMAL PHYSIOLOGY. 
remembered that diffusion is a ceaseless process in all living 
vertebrates. 
It is scarcely necessary to point out that the respiratory 
A” 
Fra, 313,—Tracings of respiratory movements of individuals belonging to different groups of 
the animal kingdom (after Thanhoffer). Differences in depth, freq , and esp ly 
BL poe , are very noticeable. 1, fish; 2, tortoise ; 3, adder (in winter); 4, boa-con- 
strictor (in summer) ; 5, oe 6, alligator ; 7, lizard; 8, canary-bird ; 9, adult dog ; 10, 
rabbit ; 11, man; 12, dog; 13, horse. Compare these, and note that in nl respiration is 
shallow, and in ml deep. 
movements are increased by exercise, emotions, position, sea- 
son, hour of the day, taking meals, etc. : 
