3$ CHEMICAL CONSTITUENTS OF BOD Y AND FOOD. 



The active radicle cannot be one which contains phosphorus, since the 

 synthesized colloids are free from that element. It may possibly be the 

 amido-fatty radicle in a high state of condensation. 



Lilienfeld and Wolkowicz, 1 by the condensation of amido-acid compounds, 

 have obtained substances which resemble proteoses in their reactions. 



Theories of proteid constitution The views of Schiitzenberger 

 on this subject will have been gathered from the preceding section. 

 There now remain to be mentioned some other theories on the subject, 

 which are in part deductions from the work of others, and partake 

 more of the nature of speculation than of hypotheses that have been 

 tested by experiment. 



Pflugers theory. The distinction between non-living proteids and 

 living protoplasm was noted as early as 1821 by Kudolphi, 2 who 

 wrote : " The components of the dead and living body do not exist under 

 the same chemical conditions." A few years later the distinction 

 between living and non-living proteids was emphasised by John 

 Fletcher. 3 PHiiger's theory 4 was, however, the first intelligible one to 

 explain such differences. The non-living proteids, such as are contained 

 in white of egg, are stable and indifferent to neutral oxygen ; but when 

 such proteids are assimilated that is, become part of a living cell the 

 molecules live by breathing oxygen. The assimilation of a proteid is 

 probably due to the formation of ether-like combinations between 

 the molecules of living proteid and the isomeric molecules of the food 

 proteid, water being eliminated ; this process of polymerisation produces 

 large and heavy but still simple molecules ; and during its occurrence 

 the nitrogen of the non-living proteid leaves the hydrogen with which it 

 is combined in the form of amidogen (NH 2 ), and enters into combination 

 with carbon to form the much more unstable substance cyanogen (CN). 

 We thus find uric acid, creatine, guanine, etc., as products of proteid 

 metabolism, while none *of such cyanogen-containing molecules are 

 obtainable from non-living proteid. 



Pfliiger's theory was put forward in 1876; but in the light of .Drechsel's 

 later work, the part involving exchange of nitrogen between cyanogen and 

 amidogen is rendered unlikely, and with that the whole theory must probably fall. 



Loews theory. The researches of Loew and Bokorny 5 have taken 

 the same direction as those of Pfliiger, in that they are attempts to 

 explain the distinction between living and dead protoplasm. Living 

 protoplasm or proteid (in the cells of various alg?e) has the property of 

 reducing silver from a weak alkaline solution of silver nitrate ; dead 

 proteid has no such effect; animal protoplasm is so quickly killed by 

 silver nitrate, that it does not give the reaction. The conclusion 

 formed is, that something of the nature of an aldehyde occurs in living 

 protoplasm. Formic aldehyde is probably formed in plants by the union 

 of carbon and water ; if this is united to ammonia, aspartic aldehyde is 

 formed, thus : 



1 Arch.f. Anat. u. Physiol., Leipzig, 1894, Physiol. Abth. S. 383 and 555. 



2 " Grundriss der Physiologic," 1821. 



3 "''Rudiments of Physiology," Edinburgh, 1837. 



4 Arch.f. d. ges. FhysioL, Bonn, Bd. x. S. 251. 



5 " Die chem. Kraftquelle im lebenden Protoplasma," Munich, 1882. Loew's most 

 recent views on this subject will be found in a recently published pamphlet, " The Energy 

 of Living Protoplasm," London, 1896. 



