126 POPULAR SCIENCE MONTHLY. 



table proteids; carbohydrates, as sugar and the starches of our cereals, 

 and fats, including those of both animal and vegetable origin. The 

 proteids are characterized by containing nitrogen (about 16 per cent), 

 while the fats and carbohydrates contain only carbon, hydrogen and 

 oxygen. The two latter classes of foodstuffs are burned up in the 

 body, when completely utilized, to carbonic acid (a gas) and water, 

 while the proteid foods beside yielding carbonic acid and water give 

 off practically all of their nitrogen in the form of crystalline nitrog- 

 enous products in the excreta of the body. Proteid foods have a par- 

 ticular function to perform, viz., to supply the waste of proteid matter 

 from the active tissues of the body, and this function can be performed 

 only by the proteid foods, hence the latter are essential foodstuffs 

 without which the body can not long survive. Fats and carbohydrates, 

 on the other hand, are mainly of value for the energy they yield on 

 oxidation, and in this connection it is to be remembered that the fuel 

 value of fats per gram is much larger than that of carbohydrates, 

 viz., 9.3:4.1, or more than twice as great. Further, it is to be noted 

 that the various foodstuffs can not be utilized directly by the body, 

 but they must first be digested, then absorbed and assimilated, after 

 which they gradually, in their changed form, undergo decomposition 

 with liberation of their contained energy which may manifest itself 

 in the form of heat or of mechanical work. The thoroughness with 

 which foods are digested and utilized in the body must therefore count 

 for a great deal in determining their dietetic or nutritive value. 

 Moreover, it is easy to see how an excess of proteid food will give rise 

 to a large proportion of nitrogenous waste matter, which floating 

 through the system prior to excretion may by acting on the nervous 

 system and other parts of the body produce disagreeable results. A 

 mere excess of food, even of the non-nitrogenous variety, must entail 

 a large amount of unnecessary work, thereby using up a proportional 

 amount of energy for its own disposal, since once introduced into the 

 body it must be digested and absorbed, otherwise it undergoes fer- 

 mentation and putrefaction in the stomach and intestines, causing 

 countless troubles. When absorbed in quantities beyond the real needs 

 of the body, it may be temporarily deposited as fat, but why load up 

 the system with unnecessary material, thereby interfering with the 

 free running of the machinery? In other words, it is very evident 

 that the taking in of food in quantities beyond the physiological re- 

 quirements is undesirable and may prove exceedingly injurious. It is 

 truly uneconomical and defeats the very ends we aim to attain. In- 

 stead of adding to the bodily vigor and increasing the fitness of the 

 organism to do its daily work, we are really hampering the delicate 

 mechanism upon the smooth running of which so much depends. 



Why now should we assume that a daily diet of over 100 grams 

 of proteid, with fats and carbohydrates sufficient to make up a fuel 



