Inheritance Materials of Germ-Cells 81 



ity is, as everybody knows, that in some way enzymes cause 

 or at least facilitate transformation in other substances. 

 Thus the attribute of solubility of the sugar into which 

 starch is transformed, through the action of the salivary 

 enzyme ptyalin, is not held to be due to a determiner for 

 solubility carried by the ptyalin and passed on into the 

 sugar, but rather it is recognized that solubility is one of 

 the attributes possessed by the kind of sugar into which 

 starch is converted by the ptyalin. The solubility is thought 

 of rather as an attribute of the sugar and not as something 

 once latent in the ptyalin which produced the sugar. A 

 few details of the action of the enzyme in this case illustrate 

 the point still better. Maltose, which is the chief if not 

 the only sugar resulting from the action of ptyalin, is not 

 reached by a single bound, as one might say, but through a 

 series of bodies known as dextrins, at least three of which 

 have been recognized. These are amylo- erythro- and 

 achroo-dextrin, named from the color they display when 

 treated with iodine, the first mentioned turning blue, the 

 second red, and the third remaining colorless. What mod- 

 ern chemist would think of explaining the blue of the amylo- 

 dextrin by a "determiner" for that color in the ptyalin 

 or even in the starch, the red of the erythrodextrin by an- 

 other determiner for red, and so on? That is the sort of 

 explaining chemists of a century ago did, but they have 

 long since learned not merely the futility but the scientific 

 evil of such explanation. 



If it were germane to our present task we might go on 

 and show that the gene conception in modern genetics is 

 really a revival in biology to-day of the gene conception 

 which passed muster in chemistry a hundred years ago, 

 when oxygen and hydrogen were named. Such an exposi- 

 tion would be appropriate to a history of scientific theory 

 or to a treatise on the theory of natural knowledge, but 

 hardly to the present work. 



