74 THE MECHANISM OF LIFE 



round them, and these waste substances go with the water into 

 the cavity of the kidney, and so down the ureter into the bladder. 



Note that the essential things in this mechanism are the cells 

 of the walls of the glomerulus and tubules. It is these cells that 

 have the power of taking water, urea, hippuric and uric acids, 

 etc., from the blood; but they do not take sugar, albumen, or 

 other things. If they do (as in diseased kidneys), that is not their 

 proper function, and the organ assumes an individuality that is 

 harmful to the organism — a disharmony is established. How 

 exactly the cells of the normal kidney function in removing 

 waste substances and nothing else we do not know. 



This is a type of glandular activity, and there are numerous 

 other organs in the body that do analogous things. The gastric 

 glands secrete hydrochloric acid and pepsin into the stomach; 

 the pancreas secretes a mixture of ferments or enzymes called 

 trypsin; the glands of the mouth secrete saliva; those of the 

 skin secrete sweat, water, oil, etc. (all waste substances), and so 

 on. In all these cases there are tubular mechanisms (as a rule 

 much simpler than those of the kidney), and these are provided 

 with nerves and arteries and veins in much the same way. There 

 are also ducts, tubes which carry the products secreted by the 

 glands to the places where they are wanted, or via which they are 

 eliminated from the body. 



But there are ductless glands also. Such are the thyroid, the 

 thymus, the pituitary, and pineal glands (see p. 99), and 

 the adrenal glands. In such cases we have glandular cells 

 surrounded by capillaries, but there is no duct and there is 

 apparently no secretion. We know, however, that there is a 

 secretion, and that this goes into the blood itself, and is then 

 carried to the rest of the body. These ductless glands are of 

 enormous importance in many ways. 



The reader will miss the true understanding of vital activity 

 if he does not note the character of unification of activity that 

 is implicit in our conception of the animal mechanism. This 

 chapter and the last one deal with mechanisms : the sensori-motor 

 system — that is, sensory organ connected with motor organ; the 

 mechanism of alimentary canal and glands that converts the 

 crude food substances into the specific proteids, fats, and carbo- 

 hydrates that are required by the animal tissues as sources of 

 energy and means of growth; the apparatus of circulation that 

 distributes these substances; the respiratory mechanism that 



