79 S THE POPULAR SCIENCE MONTHLY. 



Again, in the case of hunger, the introduction of innutritious 

 matters, as earth or sawdust, will somewhat relieve the urgent 

 sensations in extreme cases, as will also the use of tobacco by 

 smokers, or much mental occupation, though this is rather illus- 

 trative of the lessening of the consciousness of the ingoing im- 

 pulses by diverting the attention from them. But hunger, like 

 thirst, may be mitigated by injections into the intestines or the 

 blood. It is, therefore, clear that, while in the case of hunger and 

 thirst there is a local expression of a need, a peculiar sensation, 

 more pronounced in certain parts (the fauces in the case of thirst, 

 the stomach in that of hunger), yet these may be appeased from 

 within through the medium of the blood, as well as from without 

 by the introduction of food or water, as the case may be. 



Up to the present we have assumed that the changes wrought 

 in the food in the alimentary tract were identical with those pro- 

 duced by the digestive ferments as obtained by extracts of the 

 organs naturally furnishing them. But for many reasons it seems 

 probable that artificial digestion can not be regarded as parallel 

 with the natural processes except in a very general way. When 

 we take into account the absence of muscular movements, regu- 

 lated according to no rigid principles, but varying with innumer- 

 able circumstances in all probability, the absence of the influence 

 of the nervous system determining the variations in the quantity 

 and composition of the outflow of the secretions ; the changes in 

 the rate of so-called absorption, which doubtless influences also 

 the act of the secretion of the juices — by these and a host of other 

 considerations we are led to hesitate before we commit ourselves 

 too unreservedly to the belief that the processes of natural diges- 

 tion can be exactly imitated in the laboratory. 



What is it which enables one man to digest habitually what 

 may be almost a poison to another ? How is it that each one can 

 dispose readily of a food at one time that at another is quite in- 

 digestible ? To reply that, in the one case, the digestive fluids are 

 poured out and in the other not, is to go little below the surface, 

 for one asks the reason of this, if it be a fact, as it no doubt is. 

 When we look further into the peculiarities of digestion, etc., we 

 recognize the influence of race as such, and in the race and the in- 

 dividual that obtrusive though ill-understood fact — the force of 

 habit, operative here as elsewhere. And there can be little doubt 

 that the habits of a people, as to food eaten and digestive pecul- 

 iarities established^ become organized, fixed, and transmitted to 

 posterity. 



It is probably in this way that, in the course of the evolution 

 of the various groups of animals, they have come to vary so much 

 in their choice of food and in their digestive processes, did we but 

 know them thoroughly as they are ; for to assume that even the 



