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. 



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

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

 241, 275,312. 



