106 APPLIED PHYSIOLOGY 



more energy; to digest the food of cattle requires still more. The 

 lower the form of life, the more time and energy is spent in digestion, 

 and the less is the action of other parts, until the lowest forms of 

 animals simply live to eat, and remain at rest except when eating food. 

 A comparison of man's digestion with that of the lower animals is mis- 

 leading. Man's alimentary canal is designed to deal with food upon 

 which but little energy need be expended. More energy is thus avail- 

 able for his voluntary use. Because of his perfect food man can per- 

 form more labor and undergo more fatigue and exposure in proportion 

 to his size than any other animal. 



SUMMARY 



1. The digestive organs of all animals are similar to 



man's, but modified according to the needs of the 

 animal. 



2. Cattle swallow grass whole, and then chew it at leisure. 



They have four stomachs. 



3. Birds swallow food whole. It passes first into the crop, 



and later is ground in the gizzard. 



4. Insects, worms, and shellfish each possess a simple 



stomach and intestine. 



5. Man uses food which is more easily digested than the 



food of any lower animal. Thus he devotes less 

 time to mere eating and digesting food. 



REVIEW TOPICS 



1. Show in what way and for what purpose a dog's diges- 



tive organs differ from those in man. 



2. Show the use of four stomachs in cattle. 



3. Show how birds digest their food. 



4. Point out how the digestive organs are modified in 



worms ; in insects ; and in shellfish. 



5. Show what advantage man's food gives him over the 



lower animals. 



