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PHYSIOLOGICAL DEVELOPMENT. 



apparatus in its mouth, to gain by the habit of hurriedly 

 swallowing unmasticated food, it must also have the habit oi 

 regurgitating the food for subsequent mastication. This 

 correlation of habits with their answering structures, may, 

 as we shall see, arise in a very simple way. The 



starting point of the explanation is a familiar fact — the fact 

 that indigestion, often resulting from excess of food, is apt 

 to cause that reversed peristaltic action known as vomiting. 

 From this we pass to the fact, also within the experience of 

 most persons, that during slight indigestion the stomach 

 sometimes quietly regurgitates a small part of its contents as 

 far as the back of the mouth — giving an unpleasant acquaint- 

 ance with the taste of the gastric juices. Exceptional facts of 

 the same class help the argument a step further. " There are 

 certain individuals who are capable of returning, at will, a 

 greater or smaller portion of the contents of the digesting 

 stomach into the cavity of the mouth. ... In some of these 

 cases, the expulsion of the food has required a violent effort. 

 In the majority it has been easily evoked or suppressed. 

 While in others, it has been almost uncontrollable; or its 

 non-occurrence at the habitual time has been followed by a 

 painful feeling of fulness, or by the act of vomiting." 

 Here we have a certain physiological action, occasionally 

 happening in most persons and in some developed into 

 a habit more or less pronounced: indigestion being the 

 habitual antecedent. Suppose, then, that gregarious 



animals, living on innutritive food such as grass, are subject 

 to a like physiological action, and are capable of like varia- 

 tions in the degree of it. What will naturally happen? 

 They wander in herds, now over places where food is scarce 

 and now coming to places where it is abundant. Some mas- 

 ticate their food completely before swallowing it, while some 

 masticate it incompletely. If an oasis, presently bared by 

 their grazing, has not supplied to the whole herd a full meal, 

 then the individuals which masticate completely will have 

 had less than those which masticate incompletely — will not 



