158 DIGESTION IN THE LOWEE ANIMALS 



In all the warm-blooded animals the intestines are 

 much longer and more coiled than in the cold-blooded 

 forms, and the time required for the digestion of vegetable 

 matter is responsible for the greater length of the intes- 

 tines in the herbivorous animals as compared with the 

 carnivora. 



In conclusion, we may note that all modifications of 

 digestive methods are merely adaptations to meet special 

 conditions. These adaptations may take the direction of 

 specialized structures for producing digestive fluids or 

 preparation of food for the action of fluids, or thej^ may 

 be directed toward increase in surface and the insurance 

 of more complete digestion. In every case, however, the 

 transformation of food into soluble matter as a prelimi- 

 nary to absorption is the end sought, and the ultimate 

 chemical means is the action of special compounds called 

 enzjnues secreted by specialized cells. 



