THE CHEMISTRY AND PHYSICS OF THE CELL 19 



ticularly because of the confusion as to whether it includes the 

 nucleus or not, different authors differing in this respect in their 

 usage of the word. 



CHEMISTRY OF THE ESSENTIAL CELL CONSTITUENTS 



To enumerate the primary or essential constituents of the cell 

 absolutely is not possible, for the rapid advances in chemistry 

 may alter all classifications without warning, but practically they 

 may be grouped under the headings of proteids, lipoids, salts, 

 and water, and no attempt will be made to give here more than 

 the most essential features concerning each. 



PROTEIDS ! 



In the last few years we have obtained something approach- 

 ing a scientific understanding of the chemical nature of this 

 great group of the most highly complex bodies known to chem- 

 istry, although we are still far from a position where it can 

 be positively said just how the various components of the 

 molecule are united, or in exactly what proportion ; and we are 

 still farther, perhaps, from the point of synthesizing a full-fledged 

 proteid molecule. But it is believed by many chemists that the 

 problems regarding the underlying principles of the formation 

 and structure of the giant proteid molecule are nearing solution. 

 Our information has been obtained almost exclusively through 

 studies of the products obtained by splitting up the proteids, 

 for as yet little has been accomplished through synthesis. The 

 names of Kossel and Emil Fischer are most prominently 

 connected with this work. Proteids can be decomposed by the 

 action upon them of acids or alkalies in various concentrations, 

 by superheated steam, by digestive ferments, and by bacteria. 

 The products obtained in these different ways are not all the 

 same, for some substances may be formed by oxidation, reduction, 

 decomposition, combination, or condensation of the various 

 products of simple cleavage, and it is necessary to distinguish 

 between the primary cleavage products (those which exist as 

 radicals within the molecule) and the secondary products (those 

 not existing preformed in the molecule but formed by transfor- 

 mation of the primary products). This can usually be done, 

 and it is found that so far as the primary products are concerned, 

 it makes little difference which method of cleavage (or %- 

 drolysis, since in the splitting, water is combined with the organic 

 substances) is used. 



1 For the complete literature of this subject see Mann's " Chemistry of the 

 Proteids, " New York, 1906. 



