18 NUTRITIONAL PHYSIOLOGY 



the body with all its complexity as still forming a unity 

 rather than a colony. The term co-ordination is employed 

 to express this purposeful working together of all parts 

 for the advantage of the whole. The means of co-ordina- 

 tion may be chemical as just now suggested, but a more 

 conspicuous agency in the highly developed types is that 

 of the nervous system. While we must postpone until 

 a later time any detailed description, we ought to indicate 

 at this point the essential contrast between the two modes 

 of co-ordination. One part of the body may affect an- 

 other through the actual despatch of material to it. 

 When the influence is through the nervous system instead 

 of through the circulation there is no transfer of material. 

 The nerves were once supposed to convey a fluid of strange 

 properties, but the fact is established that they transmit a 

 form of energy and not of matter. (The temptation to 

 think of the nerves as conductors of electric currents and 

 to compare the nervous mechanism with a telephone 

 system is strong. Guardedly used, the comparison is 

 valuable, but it is a symbolic rather than a literal repre- 

 sentation of the facts. " Nerve impulses," so called, are 

 not electric currents in the ordinary sense.) 



In a great nation the prosperity of any section must de- 

 pend to a large degree upon the commercial exchanges 

 .taking place between that section and others. Its fac- 

 tories may depend upon the mines of another province 

 for coal and upon still another for raw material. Much in 

 the same way a single organ of the human body is de- 

 pendent upon others. A muscle, for instance, profits by 

 the prepared foods or fuels forwarded to it from the di- 

 gestive tract and by the oxygen borne to it from the lungs. 

 The blood in this case is serving the purpose which is ef- 

 fected by trains and steamers in the case of the nation. 

 Nor do we find lacking in our illustration an analogy for 

 the nervous communication between parts of the living 

 body. The type of such intercourse is furnished by the 

 telegraphic messages which pass incessantly from place 

 to place. News, in itself immaterial, may affect the course 



