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sues, e. g.^ the nature of the cell walls or iucrustiug substances. Of 

 these things ordinary chemical analysis tells us little or nothing, and 

 ■we must look to the vegetable histologist to find out about them for us. 

 Meanwhile in ignoring them -we commit more or less serious error. It 

 is, then, easy to see why, despite the useful investigation that has been 

 done of late by specialists in different lines and by the Association of 

 Ofllicial Agricultural Chemists in improving our methods of analysis, 

 the results of analyses by different chemists vary considerably from 

 one another, and our estimates of the nutritive values of feeding stuffs 

 and the results of our feeding trials are at times out of line with the 

 teachings of experience, even if the analyses were carefully made. 



In vegetable materials, by ouri)resent methods, we determine, or as- 

 sume that we determine, one group, which we call protein, by multiply- 

 ing the total nitrogen by 6.25 ; a second, which we call fats or crude fats, 

 by extracting with ether ; a third, which we call liber or crude fiGer, by 

 extracting with dilute acid and alkali ; a fourth, which we call ash, by 

 incineration ; and a fifth, which we call carbohydrates or nitrogen-free 

 extract, by subtracting the sum of the first four from the total water- 

 free substance, which last we get by subtracting from the whole weight 

 the weight of water as determined by more or less accurate dryings. In 

 animal products used for food we have no crude fiber and the quantities 

 of carbohydrates are generally so small, except in milk and its products, 

 that we neglect them. 



Protein. — This term is applied to a large number of materials which 

 differ very widely in chemical aud i)hysiological properties. Even the 

 terminology is in great confusion. We may here designate them pro- 

 teids and non-proteids. 



The proteids include the albuminoids, which are abundant in both 

 vegetable and animal materials, and the so-called gelatinoids which 

 are especially characteristic of the connective tissues of animals. The 

 vegetable albuminoids are very imperfectly understood. They are nu- 

 merous and diflicult of separation and are more or less readily trans- 

 formed into one another. The per cent of nitrogen, which should be 16 

 to make the ordinary factor 6.25 correct, varies considerably not only 

 in different classes of albuminoids but in those of the same class from 

 different species of plants, and if the results obtained by different in- 

 vestigators are to be relied on, in those of the same class from different 

 plants of the same species. With the animal albuminoids that chiefly 

 concern us the case is somewhat simpler. They appear to be less in 

 number, those which we group together are perhaps more nearly alike 

 in chemical constitution, and they change less with the growth and de- 

 velopment of the organism and in the keeping and handling in the 

 laboratory. Generally speaking the nitrogen factor 6.25 is not far out 

 of the way for them. Still we must learn much from organic chemistry 

 and histology before we can know how to separate and determine them 

 and judge of their nutritive values with accuracy. The same is true of 

 the gelatinoids, of which really but little is definitely known. 



