86 ZOOLOGY 



growth in the voice box and vocal cords in man. If the thyroid 

 is diseased or removed, so that its product is no longer poured 

 into the blood, profound changes take place in certain other 

 structures in wholly different parts of the body. If the healthy 

 thyroid tissue of another individual is grafted at any point in 

 the body of such a diseased individual the latter will become 

 normal again. These organs are believed to secrete substances 

 (hormones) into the blood which control activity elsewhere. 



Indeed we are coming more and more to understand that 

 every cell in the body changes the blood in some degree for all 

 the other cells of the body. It takes from the blood as it passes 

 and at the same time pours out into the blood the by-products 

 of its own living. We must think of the blood as more than 

 just a means of connecting lungs and intestine and kidneys and 

 the general system. The life of every cell in the body is con- 

 ditioned by the make-up of this medium whose composition is 

 determined by every cell in the body. We are just beginning to 

 appreciate its full meaning; but this chemical integration of the 

 body is profoundly important. 



c. The Coordinating Reintegration. In addition to the phys- 

 ical and chemical unity, the parts of the body must work in 

 harmony. When food is eaten the digestive glands must be- 

 come active. When the body exercises the breathing must 

 become more rapid. When an organ acts it must have an in- 

 creased blood supply. When we undertake to walk, scores of 

 muscles must contract just enough and in the right relation to 

 other muscles. When external conditions operate we must be 

 able to do the right thing. This harmony of operation among 

 the parts is coordination. Harmony between the action of the 

 organism and the outside conditions is adaptation. The nervous 

 system reintegrates these numerous diverse units of which we are 

 made, and makes them work together. All the active cells of 

 the body are connected by way of the nervous elements. A part 

 of the work of the hormones is also of this higher coordinating 

 value. It has been found by experiment that the pancreas, for 

 example, is brought to secrete at the proper time by substances 

 in the blood absorbed from the digestive tract rather than 

 through nervous action purely, as we formerly thought. 



