LECTURE VII. 



ALBUMINS OR PROTEINS. 



ELEMENTARY COMPOSITION. SIMPLE SUBSTANCES OR MIXTURES. 



CLASSIFICATION. 



THE albumins, or proteins, occupy a distinct position among our organic 

 foods. They are indispensable, and cannot be replaced by either the 

 carbohydrates or the fats. They are large factors in cell-formation, and 

 possess just as important relations to the animal organism as do the carbo- 

 hydrates to the plants. We shall see later that the animal organism 

 obtains all its albumin requirements from the vegetables. With the 

 herbivora this requirement is supplied directly; with the carnivora, indi- 

 rectly. 



The albumins present a well characterized group of compounds. They 

 differ essentially from the carbohydrates and the fats in their elementary 

 composition. Besides the elements C, H, and O, they invariably contain 

 nitrogen, and, as far as our present knowledge is concerned, also sulphur. 

 These five elements are found in proteins * in closely agreeing amounts. 

 The carbon varies from 50-55 per cent, hydrogen from 6 . 5-7 . 3 per cent, 

 nitrogen from 15-17.6 per cent, oxygen from 19-24 per cent, and the 

 sulphur from 0.3-2.4 per cent. These figures, of course, mean but little, 

 and give us no conception of the composition of the individual constituents 

 of proteins. This fact must be thoroughly appreciated, because unfortu- 

 nately many far-reaching conclusions regarding the constitution and 

 identity of albuminous bodies have been made on the basis of the ele- 

 mentary analysis. 



Before we proceed to discuss the composition of the proteins, we are 

 confronted with the question: Are we justified in considering albumin 

 itself as a well-defined, chemical individual? We shall see later that we 

 are acquainted with a large number of different proteins, which vary 

 according to their mode of formation, and, in part, their place of occurrence. 

 They all possess the common characteristic of not being able to diffuse 



1 The term proteid has been used in English as the equivalent for albuminous 

 substances (German, Eiweisskorper), although Hammarsten, Neumeister, and other 

 European authors have designated as proteids what may be called "compound proteids." 

 It has seemed best, however, to follow the German text and to designate the whole 

 group as that of the proteins. TRANSLATORS. 



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