378 HUMAN PHYSTOLOGY 



nephrin. It is applied to wounds to check bleeding, for 

 one of its effects is to cause an intense contraction of 

 small blood-vessels. This has made adrenalin valuable 

 to surgeons for work on the eye, nose, and throat. 



It has lately become probable that we must distinguish 

 between two functions exercised by the adrenal bodies: 

 they have an obscure relation to the continued welfare 

 of the system as a whole and, in addition, an occasional 

 or emergency function. This is performed under excite- 

 ment. In Chapter XII we made the point that emotion 

 is a form of exercise and accompanied by an extensive 

 discharge of impulses along various nerves. It has been 

 shown that among these streams of impulses there are 

 some which reach and arouse to unusual activity the 

 adrenal bodies. It will be well to describe an experi- 

 ment which has given proof of this effect. 



Very delicate tests for the presence of adrenin in 

 fluids have been made available. One of these tests 

 may be applied to a sample of blood taken painlessly 

 from the veins of a cat, and there will usually be no sign 

 that adrenin is present. If the test is repeated after the 

 cat has been excited by seeing a dog the secretion will 

 have made its appearance. We conclude that one feature 

 of the emotional crisis was a rapid discharge from the 

 adrenal bodies of a hormone which they ordinarily supply 

 only in minute quantities. When this discovery was 

 made it was natural to inquire whether the adrenin could 

 serve any useful purpose. The question has been an- 

 swered in the affirmative. 



It has been found that the contraction of the blood- 

 vessels which occurs under the influence of adrenin is not 

 uniformly distributed. Some areas are affected more than 

 others. The most marked constriction takes place in the 

 abdominal viscera. Meanwhile the vessels of the lungs, 

 the heart's walls, and the skeletal muscles are not con- 

 tracted at all. There will be no interference with the 

 pulmonary circulation and a positive promotion of 

 blood-flow through the muscles. A great master of 



