PROTEIDS IN PROTOPLASM. 



Chemical Relations. 



We know nothing of the precise chemical composition of 

 living protoplasm, because, as has been said (p. 2), living proto- 

 plasm cannot be subjected to chemical analysis without destroy- 

 ing its life. But the results of chemical examinations leave no 

 doubt that the molecules of protoplasm are highly complex and 

 are probably separated from one another by layers of water. 



Proteids. It has already been stated (p. 3) that the char- 

 acteristic products of the analysis of protoplasm are the group 

 of closely related substances known as proteids. But proteids 

 form only a small part of the total weight of any plant or animal,, 

 being always associated with quantities of other substances. Even 

 the white of an egg, which is usually taken for a typical pro- 

 teid, contains only twelve per cent of actual proteid matter, the 

 remainder consisting chiefly of water. The following table shows 

 the percentage of proteids and other matters in a few familiar 

 organisms and their products : 



PROXIMATE PERCENTAGE COMPOSITION OF SOME COMMON SUBSTANCES.* 

 Arranged according to richness in Proteids. 



* Compiled chiefly from tables of food-composition prepared by W. O. At- 

 water for the Smithsonian Institution, though a few examples have been added 

 viz., numbers 2, 10, 11,12, 16, from Johnson's How Crops Grow,~N. Y., 1883. 



