189 



of the ether, the strength of the acid or alkali, the time and temper- 

 ature of extraction, and by chemical changes induced in the compounds 

 by fermentation, or by long standing, or by drying in air, but also by 

 the ways in which they are held within the cells or occur as constituents 

 of the plants. The observations of the greater digestibility of cellulose 

 in young than in older jdants and in plants grown on rich as compared 

 with those grown on poor soil, iUustrate this point. We are beginning 

 to realize that the permeability of the cell walls and other mechanical 

 conditions affect the ease or difficulty of extraction ; that the histological 

 structure of the plant is a most important factor; in other words, that 

 here is one of the places where the chemist must have the help of the 

 vegetable physiologist if he will learn how to do his work as it ought 

 to be done. 



The need of an understanding of the molecular constitution of com- 

 pounds in order to devise correct methods for learning their digestibil- 

 ity and nutritive values is illustrated by the albuminoids. What is the 

 residue left undissolved by pepsin and trypsin to which the terra 

 nuclein has been applied ? Is there reason for a separate classification of 

 nucleo-albumens? Is there in these or other albuminoids a molecular 

 group containing phosphorus which resists the digestive ferments and 

 is the basis of the uudigestible portion of the compounds in which it 

 occurs? If so, what is its relation to the nucleus or the nucleolus of 

 the cell ! Shall we not have to look to a union of organic chemistry and 

 vegetable physiology for the facts wemust have in order to devise plans 

 for correct analyses and determinations of digestibility, potential energy, 

 and nutritive value of the compounds"? 



The results of future research will doubtless lead not only to changes 

 in the general groupings and methods of analysis, but also to special 

 groupings and methods of analysis for different classes of vegetable 

 and animal foods and feeding stuffs. It is hardly to be expected, for 

 instance, that we shall always hold to the same grouping of compounds 

 for grasses, cereal grains, leguminous plants and their seeds, root crops, 

 milk and meats. It is more probable that groupings for different classes 

 of materials which shall correspond with methods of analysis and of 

 estimating the nutritive values, will prove both necessary and feasible. 



It is safe to say that all of the work we have done in the past and are 

 doing to diiy in the analysis of feeding stuffs and the feeding trials based 

 upon them will have to be revised and much of it discarded. In other 

 words, a large amount of work is being done which is not bringing the 

 needed results, can not in the nature of the case be of the highest and 

 most enduring value, and much of which may have to be done over 

 again when correct methods shall have been devised. 



The first step toward reform must be research in analytical, organic, 

 physical, and phj'siological chemistry. The needed improvement of our 

 methods willevidently come only as fast as does the chemical and physio- 

 logical knowledge which must serve as a basis for changes. This 



