chap, vii The Problem of Nutrition 415 



by the living protoplasm comprise for the most part suit- 

 stances in which nitrogen is united to carbon, forming 

 cyanogen compounds, or others which, like urea, are closely 

 allied to them. Hence there arises a probability that in 

 protoplasm the cyanogen group is present. On the other 

 hand, the evidence of the hydrolysis of the non-living 

 protein by acids and alkalies as well as by the digestive 

 enzymes makes it probable that its nitrogen is united to 

 hydrogen, forming'amino-, amido-, or ammonia compounds. 

 The incorporation of the latter, or its assimilation by the 

 living substance, therefore involves according to Pfliiger 

 a rearrangement of the nitrogen atoms in the molecule, 

 which become freed from hydrogen and united instead 

 with carbon. He held that this change introduces into 

 the living matter energetic internal motion, cyanogen being 

 a radical possessing considerable internal energy. 



Pfliiger held that the arrangements of the non-nitrogenous 

 part of the protoplasmic molecule probably differs only to 

 a slight extent from that of the protein one, the products 

 of decomposition into which they enter being similar in 

 the two cases. 



After an interval of some years, some speculations, based, 

 however, upon certain observations, were put forward by 

 Loew in 1892, which are of much interest in connexion 

 with the material incorporation of protein by protoplasm. 

 He took almost the same view of the latter as did Pfliiger, 

 but he held that besides the ordinary proteins, some 

 specially labile forms can be demonstrated to exist in the 

 cell. He claimed that researches, carried on by himself in 

 collaboration with Bokorny, showed such labile proteins 

 to be present in at least 120 species of plants chosen 

 almost at random, and that they exist in leaves, petals, 

 stamens, pistils, fruits, roots, and the bark of stems. The 

 labile protein is smaller in amount in leaves in the shade 

 than in those well illuminated, and if the plant be kept in 



