PROTEIDS. 



35 



named by Mulder. According to Hoppe-Seyler they have ap- 

 proximately the following percentage composition : 



A small quantity of phosphorus is also very frequently present. 

 Associated with these elements are always small quantities of 

 various mineral substances which remain as the ash when proto- 

 plasm is burned ; but the nature of their relations to the other 

 elements is uncertain. The ash varies both in quantity and 

 chemical composition in different animals and plants. In the 

 white-of-egg the chief constituents of the ash are potassium chlo- 

 ride (KC1) and sodium chloride (XaCl), the former being much 

 in excess. The remainder consists of phosphates, sulphates, and 

 carbonates of sodium and potassium, with minute quantities of 

 calcium, magnesium, and iron, and a trace of silicon. Many 

 other mineral substances occur in association with other kinds of 

 proteids, but always in very small proportion. These salts are in 

 some way essential to the activity of protoplasm, as we know by 

 familiar experience. Man, like other animals and the plants, 

 requires certain mineral substances (e.g. common salt), but we 

 have no knowledge of the part these play in protoplasm. 



It is important to note the close chemical similarity of animal 

 and vegetal proteids, because this is one reason for regarding 

 vegetal and animal protoplasm as essentially similar in other re- 

 spects. The following table, from Johnson after Gorup-Besanez 

 and Rittliausen, shows the percentage composition of various pro- 

 teids, and proves that the difference between vegetal and animal 

 proteids is chemically no greater than that between different 

 kinds of vegetal or different kinds of animal proteids : 



PERCENTAGE COMPOSITION OF PROTEIDS. 



