November 6, 1914] 



SCIENCE 



657 



marked plasticity that is inherent to organic 

 colloidal matter, we have all the postulates 

 that are needed as a foundation upon vyhich, 

 according to the laws of physical chemistry, 

 can be built a logical explanation of the essen- 

 tial fundamental elements of the mechanism 

 of heredity. 



The inherent potentiality that determines 

 the development of the egg along a line of 

 definite sequential processes must be recog- 

 nized as being common to both animate and 

 inanimate matter and subject to the same 

 laws, so that the phenomena of living and dead 

 matter are inseparably linked and reciprocally 

 explanatory. The typical condition of matter 

 of definite composition is crystalline, and the 

 crystalline form is the result of development 

 that becomes manifested in a separation and 

 orderly and progressive arrangements of com- 

 ponents in the three dimensions of space. 

 Having a homogeneous solution of various 

 selected crystalline substances of appropriate 

 ciemical composition and constitution, and 

 given conditions attendant to crystallization, 

 the successive stages of crystalline development 

 will proceed along fixed and definitely recog- 

 nized lines, and the interactions and inter- 

 action-relationships between the various sub- 

 stances constituting the physico-chemical 

 mechanism become obvious to a greater or 

 less extent in the peculiarities of form, com- 

 position and other properties of the crystals. 

 Having in the germplasm an analogous 

 physico-chemical system, but one which is 

 markedly different especially because of its 

 organic and colloidal character and infinitely 

 greater molecular complexity and sensitivity, 

 the phenomena of development likewise pro- 

 ceed in conformity with the same laws along 

 definite lines, but they are for perfectly mani- 

 fest reasons more complex and varied, more 

 difficult of analysis, and necessarily in many 

 very important respects quite different. Each 

 step in this orderly development leads not 

 merely to changes of the physico-chemical 

 mechanism by the modification, rearrangement, 

 or splitting off of component parts, but also to 

 alterations which automatically determine the 

 characters of the next succeeding step, and so 



on to the establishment of physico-chemical 

 equilibrium and the consequent termination 

 of the reactions. 



In living matter the chemical processes ara 

 dependent to a preeminent degree upon 

 enzymes that are formed by the different 

 kinds of protoplasm to serve as implements 

 to carry out operations that are essential 

 to their existence, and such enzymes are 

 modifiable in quantity and quality in ac- 

 cordance with changes in internal and ex- 

 ternal conditions. The nature of both reac- 

 tions and products of enzymic action depends 

 upon the constitution and composition of tha 

 physico-chemical mechanism of which the 

 enzyme is an integral part. Whether or not 

 at each step of serial reactions a portion of 

 preexisting enzyme is merely modified or a 

 new enzyme is formed which constitutes an 

 essential part of the particular phase of the 

 reactions is not known, but that one or the 

 other occurs is apparently without question. 

 It has long been established that some of the 

 lower organisms, such as the yeast plant, have 

 the property of modifying the characters of 

 the enzymes produced in relation to varying 

 conditions ; recent studies of the animal organ- 

 ism show that the same phenomenon occurs 

 in both tissues and blood; and our knowledge 

 of the processes concerned in the catabolism 

 and anabolism of complex substances, such as 

 starch, is fully in support of such a conception. 

 In other words, as each step of development is 

 reached the alterations which occur in the 

 physico-chemical mechanism absolutely auto- 

 matically predetermine the characters of the 

 changes of the next succeeding step, and so on 

 to the end. Hence it follows that the pecu- 

 liarities of any given physico-chemical mechan- 

 ism predetermine the characters of the phe- 

 nomena which ensue under given conditions. 



An illustration of the probable modus 

 operandi of such a mechanism is found in the 

 phenomena of the synthesis and analysis of 

 starch: During the production of starch 

 through the agency of the chloroplast or 

 leucoplast we conceive that there are insti- 

 tuted a predetermined, orderly, independent 

 and interdependent series of reactions, the first 



