187 



The non-proteid nitrogenous compounds include those to which the 

 term amides is often applied, and which occur chiefly in plants ; those 

 which are frequently grouped with kreatin and are more characteristic 

 of animal substances; and others, such as the lecithins, alkaloids, and 

 nitrogenous glucosides which occur to greater or less extent in either 

 vegetable or animal materials or in both. They are widely divergent 

 in chemical composition, and while some of them have a high nutritive 

 value, others, including many with the highest percentages of nitrogen, 

 neither form tissue nor yield energy in the body. At i)resent there is 

 no satisfactory way of determining them. Even the methods for "non- 

 albuminoid" nitrogen in vegetable substances do not stand the test of 

 critical experience. All of them demand further investigation. 



It is perfectly clear then that the practice of determining the total 

 nitrogen, multiplying it by 6.25, calling the product protein, and using 

 it as a measure of the nutritive value of the nitrogenous ingredients is 

 a very rough and inaccurate way of doing things. 



Fats — Ether extract. — The case vrith the so-called crude fat is no 

 better. In such animal substances as muscular or connective tissue, 

 milk, and products from it, the ether extract, if obtained by proper 

 manipulation, contains the fatty bodies and little else. But the com- 

 pounds we extract from vegetable products and denominate as crude 

 fat, ether extract, or for short, fats, are very diverse, nor are we at all 

 sure what pro})ortion of them we extract by our ordinary methods. 

 We have to deal not only with the true fats, i. e. glycerides of the 

 fatty acids, and the fatty acids themselves which may be properly 

 classed with the fats in estimating nutritive values, but also with a 

 great variety of other compounds of widely differing constitution, and 

 of whose functions and value in nutrition but little is known. Au)ong 

 them are substituted glycerides including lecithins, waxes, alkaloids, 

 cholesteriu, hydrocarbons, and chlorophyls. Of these, the lecithins ap- 

 pear to have a special value in nutrition, while some of the alkaloids are 

 poisons. 



If the substance to be analyzed is finely graund, free from water, and 

 in otherwise normal condition, and the cell structure allows easy ex- 

 traction we may in general expect that ether, applied in accordance with 

 the official method which is commonly followed by the stations, will take 

 out the whole of the true fats and fatty acids, and more or less of 

 the lecithins, wax, chlorophyl, cholesteriu, alkaloids, and hydrocar- 

 bons, and that more or less of the compounds other than true fats and 

 fatty acids will remain undissolved. If the ether contains alcohol the 

 extract may be expected to contain more of the other compounds. If 

 water is present the extract may be larger, as has actually been found 

 to be the case in numerous observations. 



In other words, the extract, as obtained by the ordinary method con- 

 tains i)art or all of the fats and fatty acids and with them more or less 

 of other substances. 



There is only one way to remedy this difficulty. It is to find what the 



