GLANDS AND THE WORK OF EXCRETION 2OI 



Excretory Work of Glands. The process of removing 

 wastes from the body is called excretion. While in theory 

 excretion may be regarded as a distinct physiological act, 

 it is, in fact, leaving out the work of the lungs, but a phase 

 of the work of glands. From the cells where they are 

 formed, the waste materials pass into the lymph and from 

 the lymph they find their way into the blood. They are 

 removed from the blood by glands and then passed to the 

 exterior of the body. 



The Necessity for Excretion is found in the results at- 

 tending oxidation and other chemical changes at the cells 

 (page 107). Through these changes large quantities of 

 materials are produced that can no longer take any part 

 in the vital processes. They correspond to the ashes and 

 gases of ordinary combustion and form wastes that must 

 be removed. The most important of these substances, 

 as already noted (page 1 10), are carbon dioxide, water, and 

 urea. 1 A number of mineral salts are also to be included 

 with the waste materials. Some of these are formed in 

 the body, while others, like common salt, enter as a part 

 of the food. They are solids, but, like the urea, leave the 

 body dissolved in water. 



Waste products, if left in the body, interfere with its 

 work (some of them being poisons), and if allowed to accu- 

 mulate, cause death. Their removal, therefore, is as im- 

 portant as the introduction of food and oxygen into the 

 body. The most important of the excretory glands are 



The Kidneys. 'The kidneys are two bean-shaped glands, 

 situated in the back and upper portion of the abdominal 



1 In the oxidations that occur in the body it is not supposed that the nutrients 

 are immediately converted to carbon dioxide, water, and urea. On the other hand, 

 it is held that their reduction takes place gradually, as the reduction of sugar by 

 fermentation, and that the wastes leaving the body are but the " end products " and 

 show only the final results. 



