HEREDITY FROM PHYSICO-CHEMICAL POINT OF VIEW. 67 



beginning, in order that the nature of the essential problem should 

 be clearly defined. Our aim is to analyze into its simplest 

 physico-chemical terms so far as this is possible at present 

 this power of specific construction, of structural and chemical 

 synthesis, which is possessed by all forms of living matter. Re- 

 production and growth are different manifestations of the same 

 proliferative process. Gametic reproduction is, to be sure, the 

 most highly involved and specialized form of proliferation which 

 we know ; yet even here, as also in the case of a simple yeast-cell 

 or bacterium growing in a culture-medium, the process of con- 

 struction is accomplished through the action of the original germ 

 in incorporating and transforming physically and chemically, 

 in a definite and specific manner, certain materials (food, water, 

 salts, oxygen) taken from the surroundings. The problem of 

 just why the complex and highly organized living system thus 

 built up from a particular species of egg-cell should exhibit its 

 own specific structural, physiological, and chemical peculiarities, 

 and why these should be identical with those of the parent, is one 

 which can be solved in detail only by the special investigation of 

 that particular species. But the fact that any such special 

 development is a prolonged and complex process, involving a 

 progressively increasing differentiation and at length redupli- 

 cating the parent form, does not alter its general character as 

 proliferation. The fundamental general problem remains the 

 same, whether the process under consideration is the formation 

 of new yeast-cells or bacteria in a culture medium, or the develop- 

 ment of a higher animal from a fertilized egg. In both cases 

 material from the surroundings is transformed into living specifi- 

 cally organized substance of a constitution identical with that 

 of the parent organism. And we have to ask whether it is pos- 

 sible, in the present state of our knowledge, to form any clear 

 and consistent conception of the general nature of the physico- 

 chemical conditions under which such a result is accomplished. 



A simple concrete instance will define more clearly the nature 

 of the problem to be solved. Consider the case of a single yeast 

 cell introduced into a culture medium. The cell grows and 

 forms buds; these give rise to other buds, and cell-chains are 

 formed from which single cells detach themselves and pass 



