482 GENERAL PHYSIOLOGY 



wholly similar molecules ; such a view must be expressly rejected. 

 Protoplasm is a morphological, not a chemical conception. 1 



Extremely little is known concerning biogens, and this facb 

 should not be concealed. Since the constitution of the proteids 

 themselves, i.e., substances that can be investigated chemically at 

 any moment, is not at all known, it is readily understood that we 

 possess much less knowledge concerning the biogens, the com- 

 position of which can only be inferred from their decomposition- 

 products. It can be maintained of them only that they are extra- 

 ordinarily labile, and this property gives to them a certain simi- 

 larity to explosive bodies. Pfliiger ("75, 1) has employed certain 

 facts in a most ingenious manner for the purpose of obtaining 

 conclusions regarding certain characteristics of biogens, which 

 make intelligible the great lability of the biogen molecule in 

 comparison with the molecule of dead proteid. 



The starting-point of Pflliger's discussion is a comparison of the 

 decomposition-products that arise spontaneously and continually 

 in the oxidation of living proteid, such as in respiration, with those 

 that are obtained by the artificial oxidation of dead proteid. This 

 demonstrates the important fact that the non-nitrogenous 

 decomposition-products in the two cases agree essentially, while 

 the nitrogenous products possess not the slightest similarity. 

 " It follows from this that, as regards its hydrocarbon radicals, 

 living proteid is not essentially different from the proteid of food." 

 The important difference between the two consists rather in 

 the arrangement of the nitrogenous groups of atoms. If, however, 

 the nitrogenous decomposition-products of living proteid be 

 examined, such as urea, uric acid, creatin, etc., as well as the 

 nuclein bases, adenin, hypoxanthin, guanin and xanthin. it is found 

 that, in contrast to the nitrogenous products that appear in the 

 oxidation of dead proteid, some can be artificially prepared from 

 cyanogen compounds, while others contain cyanogen (CN) as a 

 radical. Hence it is highly probable that the carbon and the 

 nitrogen are combined in the biogen molecule into cyanogen, 

 a radical that is wanting in dead proteids. 



Thus there is presented a very fundamental difference in the 

 constitution of biogens and that of dead proteids ; this explains 

 also the great lability of the biogen molecule, for cyanogen is a 

 radical that contains a great quantity of internal energy, all its 

 compounds possessing strong inclination toward decomposition. 

 This fact enables us to understand the process of respiration, for 

 when in the biogen molecule two atoms of oxygen come into the 

 vicinity of the very labile cyanogen radical, by reason of the active 

 intramolecular vibrations of the carbon and nitrogen atoms in 

 cyanogen the carbon atom will unite with the oxygen to form the 

 very stable molecule of carbonic acid. In fact, cyanogen is very 



1 Cf. p. 80. 



