DEFINITION OF " INTERNAL SECRETION" 17 



p. 59) performed in conjunction with Bayliss, Starling has 

 made some interesting generalizations upon this type of 

 mechanism. He points out that in the normal life of the higher 

 animals, looked at as a series of reactions to environmental 

 change, the nervous system plays such a predominant part 

 that we are in danger of overlooking more primitive means of 

 co-ordination between different parts of the body. Starling 

 further points out that in the lowest animals, before the appear- 

 ance of a central nervous system, it is by chemical means that 

 co-adaptation of function is achieved. As examples he 

 mentions the movement of phagocytic cells towards an irritant, 

 the chase for food, the escape from noxious environment, or 

 the approach of sexual cells. In these cases the mechanism is 

 chemotaxis. The process of action of these stimuli must be 

 slow, and the development of a blood-circulation is necessary 

 in order to quicken it. But before this development occurs, 

 the need for quick reactions has determined the setting apart 

 of special reactive cells ; we see, in fact, the rudiments of the 

 nervous system. The whole history of the evolution of man 

 and the higher animals centres about this nervous system. 



But in some cases still, where there is no necessity for a 

 specially rapid reaction, as, for example, in the adaptation 

 of the activities of the digestive glands to the presence of food 

 in the alimentary canal, one might expect to find, as Bayliss 

 and Starling actually found, that chemical means of stimula- 

 tion are employed. Among the various hormones Starling 

 enumerates the gastric. and pancreatic hormones, as well as 

 similar bodies which determine the secretory activity both of 

 the liver and the intestinal glands, adrenin, thyroiodin, and 

 the substance secreted by the foetus during pregnancy. He 

 prophesies that with increasing knowledge the list of these 

 messenger substances will be largely extended, he points out 

 that they are comparable in many respects to the alkaloids, 

 and he intimates that the practice of drugging would therefore 

 seem to be not an unnatural device of man, but the normal 

 method by which a number of the ordinary physiological 

 processes of the organism are carried out. 



How far this attitude may be justified by future discoveries 

 must at present remain doubtful, but it certainly represents 

 the view of a large number of modern workers upon the subject 

 of internal secretion. The nervous system is no longer the 



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