THE MECHANISM OF LIFE 481 



is stored in quantity in living egg-cells in the form of vitellins, is 

 able to exist for an extraordinarily long time without undergoing 

 the slightest decomposition, if protected from bacteria. Certain 

 proteids or proteid compounds of living substance, however, are 

 continually undergoing spontaneous decomposition, even when the 

 living substance is under wholly normal conditions, and, as is 

 shown by the products that are given off, the slightest action of 

 stimuli increases the decomposition. A long time ago Pfliiger (75,1), 

 as has been seen elsewhere, 1 called attention to this important 

 difference between the proteid in dead and that in living cell- 

 substance in his valuable work upon oxidation in living substance, 

 and distinguished clearly between living proteid and dead 

 proteid. The fundamental difference between the two consists in 

 the fact that the atoms of the dead proteid molecule are in a 

 condition of stable equilibrium, while the living proteid molecule 

 possesses a very labile constitution. 



Pfltiger's assumption of living proteid, which distinguishes living 

 cell-substance from dead and in the loose constitution of which lies 

 the essence of life, is necessitated. But this substance must be of 

 essentially different composition from dead proteid, although, as 

 follows from the character of its decomposition-products, certain 

 characteristic atomic groups of the proteids are contained in it. 

 The great lability that distinguishes it from other proteids, can be 

 conditioned only by an essentially different constitution. Further, 

 critics will rightly object to the terming of this hypothetical 

 compound a " living proteid molecule, " for there is a certain 

 contradiction in calling a molecule living. The word " living " 

 can be applied only to something that exhibits vital phenomena. 

 Hence, the expression " living substance " is well justified, for vital 

 phenomena may be observed in living substance as a whole. But 

 a molecule cannot exhibit vital phenomena, at least as long as it 

 exists as such ; for if any changes appear in it it is no longer the 

 original molecule ; and, if it continues unchanged, vital phenomena 

 are not present in it. The latter, which are based upon chemical 

 processes, can be associated only with the construction or the 

 destruction of the molecule in question ; and thus the application 

 of another name to the compound that is at the focus of life is 

 doubly justified. In order to distinguish this body, therefore, from 

 dead proteid and to indicate its high significance in the occurrence of 

 vital phenomena, it appears fitting to replace the term " living 

 proteid" with that of liogen. The expressions "plasma 

 molecule," "plasson molecule," " plastidule," etc., which Elsberg 

 ('74) and Haeckel (76) have employed, and the conceptions of 

 which are comprised approximately in the expression " biogen 

 molecule," are less fitting in so far as they easily give the impression 

 that protoplasm is a chemically unitary body, which consists of 



1 Cf. p. 304. 



I I 



