222 THE ENGINES OF THE HUMAN BODY 



the ranks. Thus millions of men are knit together to 

 act as a single machine by the employment of various 

 systems of communication, some of which act slowly, 

 others almost instantaneously. We are to see that the 

 units of the human machine are also linked together by a 

 dual system — a postal and a telegraphic. 



That the human body was provided with a quick- 

 acting or telegraphic system, medical men have known 

 for hundreds of years. From its brain and spinal cord — 

 the G.H.Q. of the human machine — they could see great 

 cables of nerves issuing in all directions, linking the 

 various members to the controlling centres". They knew 

 that messages sped along the wires of the nerve cables, 

 carrying orders and information from and to the com- 

 mander-in-chief and the various departments of his staff. 

 It is surprising to think that it is only in quite recent 

 years that we began to suspect that the human body was 

 also provided with a postal system. Our previous blind- 

 ness was all the more remarkable because we knew that 

 great colonies of simple units, such as make up living 

 corals and sponges, did communicate with and con- 

 trol each other, and yet, as was well known, these 

 colonies were unprovided with nerve systems. We 

 were also aware that among primitive peoples, like 

 the aborigines of Australia, there was neither postal 

 nor telegraphic systems ; one tribe communicated with 

 another by sending out a messenger carrying a stick on 

 which certain symbols were rudely carved. We ought 

 to have suspected that, in the evolution of the human 

 body, a postal system would precede a telegraphic one. 

 That was not so, however. The first clear recognition 

 that the human body possessed a postal as well as a tele- 

 graphic system was made by Professor Starling in 1904. 

 The circumstances under which his discovery was made 

 were mentioned in a former chapter while describing the 

 mechanism which sets the pancreas in action (Chapter 

 XIX., p. 199). Professor Bayliss and he found that the 

 pancreas began to form and pour out its digestive juice 

 upon the receipt of certain missives which were posted 



