230 TEXTBOOK OF PLANT PHYSIOLOGY 



group, NH 2 , but in the form of the cyanic group, C|N, which 

 gives them a special instability and high capacity of transforma- 

 tion; two essential properties of life. This theory was first advanced 

 by Pfluger, and was supported for a long time by Loew and 

 Bokorny, who by means of a special aldehyde reaction attempted 

 to distinguish chemically between living and non-living proteins. 

 The most recent biochemical investigations do not support this 

 idea, and therefore we have no reason to believe that the proteins of 

 protoplasm are especially unstable. Quite the contrary, in their 

 relation to enzymes and to many chemical reagents they are 

 usually more stable than the reserve proteins. 



In general, the chemical composition of protoplasm has not yet 

 been sufficiently studied, since it usually occupies only an incon- 

 siderable part of the whole volume of the cell, and is very difficult 

 to separate from the substances found in the cell sap. 



The most convenient objects for the study of protoplasm are the 

 Plasmodia of slime molds (Myxomycetes), which are large aggre- 

 gates of naked protoplasm. A careful analysis performed compar- 

 atively recently by Kiesel (1925) gives the following percentage 

 composition of the Plasmodium of one of these molds (see table 

 below). 



In this instance, of course, not only the active protoplasm, but 

 also a number of reserve substances have been included, as evi- 

 denced by the presence of glycogen and certain characteristic 

 fractions of the fats and proteins. A full separation of the reserve 

 substances from the active ones, however, is hardly possible, since 

 for their work the active parts of protoplasm continually require 

 reserve substances, which are always present within the cell. 



Per Cent 



Fats 17.85 



Lecithin 4 . 67 



Cholesterol 0.58 



Mono- and disaccharides 8 06 



Polysaccharides (largely glycogen) 17.02 



Soluble nitrogenous substances 12.00 



Proteins (including those of the nucleoproteins) 20 . 65 



Plastin 8.42 



Nucleic acid 3 68 



Fats from lecithoproteins (?) 1 . 20 



Unknown substances 5 . 87 



Total 100.00 



