CHAPTER XXXIX 



DIGESTION 



Introduction. The alimentary canal is a series of 

 small chemical laboratories, in each of which are special 

 digestive fluids. These are chemicals which act, each in 

 a special way, upon the foods with which they come in 

 contact. This whole process we call digestion. 



Necessity of digestion. We 

 have learned in our labora- 

 tory exercises that if molasses 

 and water are separated by 

 an animal membrane, diffu- 

 sion takes place in both direc- 

 tions. We did not learn, 

 however, that all liquids 

 would not behave in this man- 

 ner. If we used olive oil or 

 the white of egg, the results 

 would be very different. 

 Neither the egg nor the oil 

 would diffuse. 



In order that the food 

 which we eat may be utilized, it must leave the ali- 

 mentary canal and be taken to all parts of the body 



321 



Fig. 154. Experiment show- 

 ing diffusion. The liquid in 

 the thistle tube is separated 

 from that in the jar by an 

 animal membrane. 



