PFLUGER'S THEORY 77 



the interaction of the colloidal material with various 

 elements, notably oxygen. Under favourable con- 

 ditions dead albumin remains intact for an indefinite 

 time. But living albumin decomposes readily under 

 the influence of external excitement. The cause of 

 this instability is due to intra-molecular changes, 

 mainly produced by oxygen, by which the molecule 

 undergoes cleavage and new groups are formed. 

 Pfliiger believes that the characteristic peculiarity of 

 proteids and the real cause of the instabilty of living 

 proteids is due to the presence of a cyanogen radical 

 in the molecule. 



We have seen carbon and nitrogen joined together 

 by one or two valencies. They may also be joined 

 together by three valencies, forming thereby cyano- 

 gen, CN, in which the nitrogen is a triad and one 

 valency of the carbon remains free. They may also 

 be joined together by four valencies, as in iso- 

 cyanogen, in which case the nitrogen is a pentad 

 occupying the four valencies of the carbon atom and 

 leaving one of its own valencies free. 



When nascent hydrogen, the H ion, is joined to the 

 CN group it forms hydrocyanic acid, HCN, which 

 occurs in amygdalin and other vegetable compounds. 

 This acid will combine with iron, potassium, etc. 

 The cyanogen radical or CN ion may also combine 

 with alcohols by displacing one atom of hydrogen, as 

 in the case of cyanhydrine, C 3 H 5 NO or C 2 H 5 0-CN. 

 The cyanhydrines are regarded as important sub- 

 stances in biological construction. 



The cyanogen radical may also join in different 

 ways with OH ions. One of these combinations is 

 cyanic acid, CN-OH, which forms salts with various 



