74 THE THEORY OF IONS 



Others consider that living proteids consist of chains 

 of cyanhydrines connected with benzene nuclei. 

 All this is, however, mere paper speculation with 

 but a very slender basis of facts."* 



At the moment of death the proteids become 

 changed in character ; they are more stable, and 

 capable of being subjected to chemical investiga- 

 tion. As the result of such research Fischer, Sieg- 

 fried, Curtius, and others, have been able to show 

 that the dead proteins consist of a mixture of amido- 

 or amino-acids, and can be broken down to these by 

 hydrolytic cleavage. The amido-acids are, as we 

 have seen, ammonium salts of the fatty acids. But 

 how these acids are linked together to form the 

 molecule of living proteid, how they are influenced 

 by the introduction or abstraction of H, OH, NH 2 

 and CH 2 or other ions, is not exactly known. That 

 the proteid molecules are so influenced we know ; 

 changes are produced by oxidation, hydration, and 

 dehydration which completely alter their character. 



The proteins are formed exclusively by plants, so 

 far as we know. Chlorophyll, as we have seen, 

 forms aldehydes out of the ions arising from the 

 cleavage of C0 2 and water. Successive changes 

 lead to the formation of aspartic aldehyde and 

 aspartic acid. The latter is amido-succinic acid, 

 and when ammonia displaces one of its hydroxyls it 

 forms asparagine, which is also one of the amido- or 

 amino-acids. 



C 4 H 7 N0 4 + NH 3 C 4 H 8 N 2 3 + H 2 0. 



Leucine (C 6 H 13 N0 2 ) is amido-iso-caproic acid 

 formed by ammonia attaching itself to iso-butyl- 



* Moller, ibid., p. 431. 



