CHAPTER IX 



DIGESTION 



ALIMENTARY CANAL— BODY-CAVITY— DIGESTION— 

 HORiAlONES AND VITAMINS— CALORIES— APPETITE 



"The process of digestion, as I have been informed by ana- 

 tomical^ friends, is one of the most wonderful works of nature. 

 I do not know how it may be with others, but it is a great 

 satisfaction to me to know, when regahng on my humlile 

 fare, that I am putting in motion the most beautiful machinery 

 with which we have any acquaintance. I really feel at such 

 times as if I was doing a public service. When I have wound 

 myself up, if I may employ such a term," said Mr Pecksniff with 

 exquisite tenderness, "and know that I am Going, I feel that 

 in the lesson afforded by the works within me, I am a Bene- 

 factor to my Kind." 



Mr Pecksniff. Martin Chuzzlewit. Chaeles Dickens. 



Alimentary Canal 



1 HE simplest of multicellular animals, Metazoa, such as 

 the sponges, are compact but honey-combed by channels 

 through which water with food suspended in it circulates. 

 They have no mouth or stomach. They are all aquatic and 

 their food is taken in by the cells exposed to the water. These 

 cells behave like so many Amoebae. A little higher up in the 

 scale, in certain Turbellaria, there is a mouth and a stomach, 

 like the inner, closed tube of a thermos-flask. Each of the 

 cells lining this cavity eat up the food-particles in an amoeboid 

 manner. In the parasitic flukes, Trematoda, the stomach 

 branches so that the food is brought into close contact \\ith 

 all the cells of all the tissues of the solid body. In such animals 

 undigested food, if any, passes out througli the mouth. The 

 larvae of bees feed on a perfect diet, "pap" or "royal jelly" 

 at first, and then after four days a little honey is added, 



1 In Mr Pecksniff's time the physiologist had hardly emerged from the 

 anatomist, and what little physiology was taught in our Hospitals and 

 Universities was taught by the Professors of Anatomy. 



