34 



PROTOPLASM AND THE CELL. 



animal, being always associated with quantities of other sub- 

 stances. Even the white of an egg, which is usually taken for 

 a typical proteid, contains only twelve per cent of actual proteid 

 matter, the remainder consisting chiefly of water. The follow- 

 ing 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. 



All proteids have nearly the same chemical composition and 

 similar physical properties, however different may be the forms 

 of protoplasm in which they occur. The analysis of protoplasm, 

 or rather of the proteids which are its basis, teaches us really 

 nothing of its vital properties, but serves only to show the 

 chemical composition of the material basis by wh'ch these are 

 manifested. 



Proteids are so called from their resemblance to protein 

 s", first), a hypothetical substance first described and 



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

 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. 



