94 THE BODY AT WORK 



the body had to establish its claim to be regarded as useful 

 before it became entitled to share in the common supply of 

 food ; so, at least, we are disposed to think. But, tempting 

 though it be to attribute to sheer conservatism the retention 

 of .an organ which has been superseded in its original functions, 

 and for which we cannot recognize any new use, it is a tempta- 

 tion which must be severely checked. It is safer to suppose 

 that the fact that it has been retained is prima-jacie evidence 

 that the body has need of it. 



There can be no doubt as to the importance of the internal 

 secretions of the three chief ductless glands. What about 

 other organs the glands which make external secretions, for 

 example ? Does each of them make also an internal secretion 

 which influences the activity of other organs ? It is very 

 difficult to prove the production of internal secretions by such 

 organs as the salivary glands, the pancreas, the kidneys, because 

 all the effects which result from their removal may be due to 

 the suppression of their external secretions. It is almost im- 

 possible to distinguish the consequences which might be due 

 to the abolition of an internal secretion from those which 

 ought to be attributed to the loss to the body of the chief 

 functions of the organ. Certain physiologists are inclined to 

 think that all organs not only the glands, but the liver, 

 spleen, muscles, etc. produce chemical messengers which are 

 discharged into the blood ; and recent discoveries tend to jus- 

 tify this view. As the time approaches when milk will be 

 wanted for the nourishment of offspring, it begins to appear in 

 the breast. Hitherto this has been attributed to nervous control. 

 It is now known that the secretion is provoked by a chemical 

 messenger. If this messenger, extracted from the organ in 

 which it is formed, be injected into the veins of an animal 

 which has no call to secrete milk, it sets up a condition of 

 activity in its mammary glands. Such an illustration of the 

 possibilities of chemical, as distinguished from nervous, control 

 inclines us to attribute the harmonious working of the body 

 in large measure to the mutual influence of its several parts, 

 instead of invoking in every case, as used to be the custom, 

 the directing power of a somewhat bureaucratic nervous 

 system. 



It is curious to note that an internal secretion is essentially 



