408 HUMAN PHYSIOLOGY 



Hence the emptying of these veins always drives blood 

 in the direction of the heart while they refill from the tis- 

 sues. This accelerating influence is lost when long-sus- 

 tained contractions are made, as in carrying a suit case. 



The hastening of the blood-flow by the pressure of 

 contracting muscles is a kind of massage and its effect is 

 extended to the contents of the lymphatics. The fact 

 has been noticed in Chapter XVII. There is every rea- 

 son to believe that it assists in the removal of waste and 

 promotes the nutrition of the regions where the condition 

 is operative. 



The beneficial results of muscular activity so far as 

 they are manifest in the digestive system are indirect 

 but important. The immediate consequence of activity 

 must always be a withdrawal of blood from the alimen- 

 tary canal. This cannot, in itself, be other than a 

 hindrance to the processes going on there. It is likely 

 that excessive perspiration leads to a shrinkage in the 

 volume of the juices. But in spite of these unfavorable 

 features we know that the net outcome is in favor of the 

 man who takes a fair amount of exercise. To some 

 extent his digestion may be helped by the actual agitation 

 of the canal. A far more significant reward is the sharp 

 appetite which usually presages a successful disposition of 

 the meal. 



The Fundamentals of Sex Hygiene. Here is a matter 

 which is much more widely and freely treated now than 

 it was a few years ago. There must always be an in- 

 clination to reticence on the subject and for the best of 

 reasons. The abnormal side of sexual life is abhorrent 

 to normal individuals. The normal side is limited to the 

 sacred intimacy of marriage and should remain inviolate. 

 But there are a few cardinal principles of thinking and 

 conduct which it cannot be an offense to publish. 



The sexual instinct in the average man is a compelling 

 one. This being true, it is plainly his duty to see to it 

 that it shall not progressively encroach upon the sphere 

 of other interests. This is precisely what it will do if the 

 line of least resistance is followed. There are men 



