BLOOD-MAKING 



as fine as a hair, and in consequence are called capillaries. 

 The blood returns to the heart, not by the way it came, 

 but by wholly different vessels called veins. The blood 

 renews the tissues of the body, which even the simplest 

 acts of our daily life wear and destroy, which is the 

 reason we are tired after great exertion and the weari- 

 ness lasts until we have rested and given the blood an 

 opportunity of repairing the damage. 



Digestion. The process of digestion is really blood- 

 making. Food is taken into the mouth, where it under- 

 goes not only the process of mastication, or chewing, but 

 something else of the utmost importance. The saliva, 

 which pours out from the membrane of the mouth, 

 converts the insoluble 

 starch contained in so 

 much of our food into 

 sugar, which is a soluble 

 substance, and is easily 

 absorbed and dissolved in 

 the blood. In the stomach 

 the food is ground and 

 churned up with a fluid 

 called the gastric juice. 

 Unlike the saliva, this fluid 

 will not act upon starches, 

 but it will dissolve lean meat 

 and the glutinous parts of 

 bread and other substances. Fats and the oily parts of 

 our food are unchanged even after their passage through 

 the mouth and stomach. It is not until the partly digested 

 mass reaches a long tube, called the intestine, that the 

 liver supplies another fluid, called the bile, to extract the 

 remaining nourishment. The stomach constantly gives up 

 to the blood-vessels all around the food which it has fully 

 dissolved ; and as the remainder passes along the intestinal 

 canal all that is of value is finally absorbed into the blood, 

 leaving the waste, the useless undigested material, to be 

 expelled from the body. 



Teeth. Intimately connected with the process of diges- 

 tion are the teeth, the arrangement of which is highly im- 



THE HUMAN STOMACH. 



Pylorus, the ' gateway ' into the 

 Duodenum, or first intestine. 



