46 The Significance of Chemical Molecules 



the plastidules, and not enter into the speculations on the 

 undulating motion of these particules. But, in critically 

 discussing that part, we can emphasize here the fact that 

 the theory is composed of two hypotheses : 



1. Protoplasm is made up of numerous small units, 

 which are the bearers of the hereditary characters. 



2. These units are to be regarded as identical with 

 molecules. 



The first of these two hypotheses has obviously very 

 great advantages. It explains the fundamental phenom- 

 ena of heredity in a simple manner, and especially ac- 

 counts sufficiently for the independence and miscibility 

 of the individual hereditary characters. It is identical 

 with the first law of Darwin's pangenesis, as we shall see 

 more in detail in the third Chapter. We shall, therefore, 

 put off a more thorough discussion, especially as Elsberg 

 wrote a few years later than Darwin, and in not nearly 

 as clear a manner. 



Let us now turn to a criticism of the second thesis. 

 Elsberg never expresses himself clearly about the identity 

 of his plastidule with chemical molecules. He defines 

 them as the smallest particles of a cell in which the hered- 

 itary characters lie hidden.^ These particles must be 

 larger than the molecules of the ordinary protein bodies ; 

 this follows from their much more complicated character. 

 Haeckel, however, devotes a detailed discussion to this 

 identity.^^ 'The plastidules possess, first of all, every 

 quality which physics ascribes generally to the hypotheti- 

 cal molecules, or combined atoms. Consequently each 

 plastidule cannot be analyzed any further into smaller 

 plastidules, but only into its component atoms. ..." 



i^Elsberg. loc. cit. p. 9. 

 I'^Perigenesis loc. cit. pp. 35-36. 



