86 ZOOLOGY 



In becoming suited to doing one kind of work the cells cease to 

 be able to do other kinds. The various cells thus become mutu- 

 ally dependent. Unless they can be brought to work together 

 suitably there will not be efficiency. Division of labor is only 

 one-half of efficiency. There must also be a reintegration of 

 these special parts into a higher kind of oneness. It is this that 

 determines the state of the individual made up of these special- 

 ized parts. There are three phases of this reintegration. 



a. Physical Reintegration. — This is done by the cement be- 

 tween cells, by the connective tissues, the skin, the skeleton, 

 and similar tissues. When the fertilized egg first divided, this 

 cement held the cells together. It is only in this way that a 

 multicelltilar animal could arise. In the mature body the bil- 

 lions of cells are further bound together by these connecting tis- 

 sues into a physical unity that makes it possible that they work 

 together as they could not do if they were not united into one 

 body. 



h. Nutritive Reintegration. — This physical bond would mean 

 little but for a deeper one. In the differentiation of the cells, 

 while all must have food and oxygen and all produce wastes 

 which they must get rid of, the various cells of the body do differ- 

 ent things. They have somewhat different needs and produce 

 different kinds of waste products. Some cells absorb the foods 

 for all; others absorb oxygen. Some eliminate carbon dioxid 

 from the system; others eliminate the urea and other wastes 

 for all the cells; still others manufacture substances which are 

 of further use in the general work of the body. It follows there- 

 fore that all these cells must be connected in a chemical or 

 nutritive way. This is done by the body fluids, including 

 chiefly the blood and lymph. 



In addition to the work of lungs, digestive epithelium, the 

 skin, and the kidneys referred to above, with which all the active 

 cells of the body must be connected in this chemical interchange 

 — the liver, the spleen, the sex glands, the thyroid, the adrenals 

 and other groups of cells take from or add to the blood sub- 

 stances that vitally change it. Very often these special sub- 

 stances poured into the blood by particular organs, as the testes 

 or the thyroid, will be carried all over the body by the blood and 



