230 THE ENGINES OF THE HUMAN BODY 



by a profuse overgrowth of the rind of the adrenal glands. 

 In these glands are manufactured missives which have to 

 do with the growth of sex characters. Professor Bulloch 

 and Dr Sequeira were the first to perceive the relationship 

 between a manifestation of sexual precocity and a patho- 

 logical overgrowth of the adrenal bodies. The sexual 

 glands also use the pituitary laboratory in effecting the 

 display of secondary sexual characters. Even in the 

 regulation of the size of our bodies, the quality of 

 our minds, and the cast of our countenances Nature 

 has designed and set in motion a wonderfully organised 

 machinery. 



Mention was made, when surveying the third great 

 chemical laboratory of the alimentary tract (Chapter XX., 

 p. 215), of the immense and movable armies of micro- 

 scopic corpuscles which could be mobilised for police 

 or sanitary duties. So far, however, we have given no 

 indication to the reader of the busy traffic carried on by 

 white corpuscles. They swarm in the blood stream as it 

 circulates round the body. There are various kinds of 

 them, and we shall learn the nature of their duties as our 

 modern investigations proceed and fructify. But it is 

 extremely probable that one variety of them, if not more, 

 are really errand-boys on their way to deliver messages or 

 parcels, and that the gland masses which are built up in 

 and round lymph channels serve both as nurseries for the 

 upbringing of such messengers and also as offices from 

 which they are dispatched on their errands. 



In this chapter we seem to have gone a long way from 

 the Simple idea with which we set out — a comparison of 

 the human machine to a motor cycle. Our comparison 

 held very well, and was instructive, so long as we looked 

 on the human body as a moving machine furnished with 

 muscular engines, levers, pumps, and bellows. It was 

 when we came to deal with the laboratories in which the 

 fuel for the machine is prepared that a strict comparison 

 between the body and a machine of metal became more 

 difficult to uphold. When we looked beneath the surface 

 of the alimentary laboratories we discovered that their 



