The Process of Life. 25 



process thus so differently manifested. ? Clearly the 

 supply of oxygen to the cellular tissue-elements, and, 

 generally closely associated with this, the getting rid of 

 carbonic acid gas. 



Let us now glance at the life-processes which minister 

 to nutrition, beginning, as before, with the mode in which 

 these processes are effected in ourselves. 



The alimentary canal is a long tube running through 

 the body from the mouth to the vent. In the abdominal 

 region it is coiled upon itself, so that its great length may 

 be conveniently packed away. Opening into this tube are 

 the ducts of certain glands, which secrete fluids which aid 

 in the digestion of the food. Into the mouth there open 

 the ducts of the salivary glands, which secrete the saliva ; 

 in the stomach there are a vast number of minute gastric 

 glands ; in the intestine, besides some minute tubular 

 glands, there are the ducts of the large liver (which 

 secretes the bile) and the pancreas, or sweetbread. Since, 

 with the exception of the openings of these ducts, the 

 alimentary canal is a closed tube, its contents, though 

 lying within the body, are in a sense outside it, just as the 

 fuel in a tubular boiler, though within the boiler, is really 

 outside it. The organic problem, therefore, is how to get 

 the nutritive materials through the walls of the tube and 

 thus into the body. 



At an ordinary meal we are in the habit of consuming 

 a certain amount of meat, with some fat, together with 

 bread and potatoes, and perhaps some peas or beans and 

 a little salt. This is followed by, say, milky rice-pudding, 

 with which we take some sugar; and a cheese course 

 may, perhaps, be added. The whole is washed down with 

 water more or less medicated with other fluid materials. 

 Grouping these substances, there are (1) water and salts, 

 including calcium phosphate in the milk ; (2) meat, peas, 

 milk, and cheese, all of which contain albuminous or allied 

 materials ; (3) bread, potatoes, and rice, which contain 

 starchy matters ; and here we may place the sugar ; (4) 

 fat, associated with the meat or contained in the cream of 



