6 PROTOPLASMIC ACTION AND NERVOUS ACTION 



of protoplasm/ This consideration is overlooked in 

 many '' theories of heredity/' which apparently take for 

 granted the existence of the property which they are 

 called upon to explain. Ids, pangenes, chromosomes, 

 and the other representative particles of these theories 

 are self-multiplying units; i.e., they possess ex hypothesi 

 this automatic power of synthesizing material and 

 structure of their own kind. It is well, therefore, to 

 realize clearly the fundamental identity of the physi- 

 ological conditions underlying all of the phenomena 

 grouped under the foregoing head. 



To prevent any possible misunderstanding, a few 

 words may be added here concerning the nature of the 

 physiological problems raised by the chromosome 

 theory of heredity, which now seems to be established 

 on a secure basis through the correlation of genetic and 

 cytological investigation.^ 



All the evidence indicates that the chromosomes, 

 the carriers of genetic factors or "genes," are the elements 

 or units in a sorting and distributing mechanism, by 

 means of which special formative metabolic processes 

 are localized in definite regions of the growing and 



^ Haldane's remarks in his British Association address of 1908 

 {Nature, LXXVIII, 555), "nutrition itself is only a constant process of 

 reproduction" and "heredity is for biology an axiom and not a prob- 

 lem," do not dispose of the problem of heredity, but apparently assign 

 it to a border-line position, somewhere between chemistry and biology. 

 The property of automatic specific synthesis is the one to be explained. 

 The original natural systems which exhibited this property were pre- 

 sumably the ones from which living organisms, as we find them, have 

 evolved. 



2 Cf . T. H. Morgan, The Physical Basis of Heredity, Philadelphia 

 (1919); also "The Mechanism of Heredity," Nature, CIX (1922), 

 241, 275, 312. 



