92 



"De enzym-theorie der erfelijkheid" (The Enzyme Theory of Heredi- 

 ty) 1 ). The writer believes that the cause of the scantiness of the regard 

 evoked by this paper is to be found in the terminology used in it. 



BEIJERINCK postulates the following in his treatise. The protoplasm 

 is built up by a large number of factors, w^hich determine the heredit- 

 ary characteristics of the organism, and which multiply with the cell- 

 division. They received various names and are called - - as stated by 

 BEIJERINCK- "differirendeZellelemente (MENDEL), gemmules (DAR- 

 WIN), biophores, pangenes, genes, character units, heredity units, 

 Mendelian factors, or factors". We emphasize that the nucleus is not 

 taken in consideration herein. BEIJERINCK considers the relation 

 between the protoplasm and the cell nucleus as a separate problem 

 which, however, must be treated parallel to the idea just formulated. 



There certainly are strong arguments in favour of BEIJERINCK'S 

 conception of the "factors". It is in accordance with the older con- 

 ceptions. In DE VRIES' "Intracellulaire Pangenesis" 2 ) one finds in 

 italics, as the main thought: "Das ganze lebendige Protoplasma be- 

 steht aus Pangenen; nur diese bilden darin die lebenden Elemente". 

 DE VRIES means with this protoplasm the nucleus as well as the cyto- 

 plasm. In the definition which W. JOHANNSEN (Elemente der exakten 

 Erblichkeitslehre 3 ), 2. Aufl. 1913, S. 143) gives of gene, and in which 

 he emphatically states that he therewith concurs with the conception 

 pangene, a still wider significance is given to the word gene, and it is 

 stated, in spaced letters: "Das Wort Gen ist also frei von jeder Hypo- 

 these". JOHANNSEN wishes to express with the conception "genes" 

 only the occurrence of properties "in separable form", so that they 

 can be encountered in different combinations in the gametes and the 

 zygotes. It is remarkable, however, that in the modern study of 

 heredity, notwithstanding the fact that it is historically incorrect, 

 there is a strong tendency to use the conception "genes" exclusively in 

 connection with the nucleus. On p. 508 of the 5th edition of R. GOLD- 

 SCHMIDT'S excellent "Einfuhrung in die Vererbungswissenschaft" 4 ) 

 it is said, for instance: "Wie arbeiten die Gene im Kern - - und nur 

 solche kennen wir bisher - - mit dem Plasma in dem gesamten jeweili- 

 gen System (Eizelle, Keim) zusammen?" 



If this difference in conception \vith respect to "factors" or "genes" 

 is kept in mind, then BEIJERINCK'S considerations become clear im- 

 mediately. Further considerations about his experience on exo- and 

 endo-enzymes convinced him, namely, that enzymes also must be 

 considered as partly living protoplasm (however living protoplasm 

 must not be considered as a simple mixture of enzymes ; some enzymes 

 for instance, may first become active in certain stages of the develop- 



') Proceedings of the Section of Sciences, Kon. Akademie van Wetenschappen Am- 

 sterdam 19, 1275-1289, 1917 (Verzamelde Geschnften 5, 248-258). 



2 ) Jena 1889. 



3) Jena 1913. 



4 ) B?rlin 1928. 



