ECONOMY OF THE BODY 139 



be contributed to the blood by a particular organ and 

 distributed through the body with very effective results, 

 especially in certain parts. The word " hormone," which 

 means excitant, was invented by Mr. W. B. Hardy in 

 connection with the remarkable discovery of " secretin " 

 by Professors Bayliss and Starling in 1902. This substance 

 " secretin " is produced in the presence of acid by the cells 

 lining the beginning of the small intestine ; it is carried 

 away by the blood-stream and it excites the pancreas or 

 sweetbread to secrete its very important digestive juice 

 which is poured into the food-canal. Thus, when a meal 

 is in process, or it may be in prospect, there is by means of 

 the excitant secretin a preparation for its digestion, and 

 this illustrates what is meant by physiological co-ordination 

 or correlation. For it is plain that the beginning of the 

 intestine and the sweetbread work into one another's hands. 

 Although the word hormone really means excitant or stirrer- 

 up, a wider idea was from the first associated with it, namely, 

 that of " chemical messenger " ; as Sir Edward Schafer 

 points out, it might have been happier to have thought of the 

 messenger of the gods and made the word not " hormone " 

 but *' hermone." But this is being wise after the event, 

 and although there are hormones which inhibit instead of 

 exciting, the word has come to stay. The internal secretion 

 by which ductless glands and specialised patches of tissue 

 produce hormones is conveniently defined as follows by 

 Professor Swale Vincent : " The process consists in the 

 preparation and setting free of certain substances of physio- 

 logical utility (the raw materials for which are supplied by 

 the circulating blood) by certain cells of a glandular type ; 

 the substances set free are not passed out on to a free 

 surface, but into the blood-stream." It is not too much 

 to say that the discovery of the role of hormones has changed 

 the whole face of physiology. It has also added incalcul- 

 ably to the biological control of life. 



It may be that even in plants there are analogues of 

 hormones, chemical messengers by which one part can 

 influence another at a distance ; and it may be that future 



