180 LIFE: ITS NATURE AND ORIGIN 



The notion that many happenings in morphology and dif- 

 ferentiation are understandable on the basis of the direction of 

 chemical change by specific catalysts existing initially in the fer- 

 tilized egg, or formed or modified in the developing embryo, 

 seems consonant with the experimental data. The formation of 

 various structures — catalysts, cells, organs, tissues — of specific 

 nature and at definite times and places in the developing or- 

 ganism depends upon the formation and assembly of a wide 

 variety of specific chemical molecules at suitable rates, in suitable 

 ratios, and at suitable times and places. Apart from formation 

 in situ, the assembly and distribution of small material units is 

 controlled by such factors as Brownian motion, convection, cir- 

 culatory systems and especially by selective adsorption and dif- 

 ferential diffusive mobility. But catalysis is the basic mechanism 

 whereby are produced the particular chemical units which under- 

 lie metabolism, development and growth. Catalysis makes these 

 descriptive terms mechanistically and materially intelligible. 

 Without a mechanism they are symbols for unknowns. 



When we consider the numerous catalysts and chemical changes 

 dominating what was supposed to be the comparatively simple 

 breakdown of glucose by yeast into alcohol and carbon dioxide, 

 and recall that catalysts may synthesize as well as decompose mole- 

 cules, we may well stand aghast at the catalyst-based chemical and 

 physico-chemical complexities emerging in a single cell. Further- 

 more, when we remember that most of the happenings observed 

 and recorded by biologists lie at or above microscopically visible 

 structural levels, it is astonishing to see the wealth of information 

 that has been deduced from critical experiments, which often 

 reach far below what is seen. For example, the presence and 

 location of sulphydryl groups ( — SH), which among many other 

 potencies affect the activity of many proteases (catalysts directing 

 protein formation, alteration or destruction), may be made evi- 

 dent by the nitroprusside test. Glutathione, important in growth 

 and containing the — SH group, is thus revealed to be present in 

 the blastoderm* of the chick, but not in the yolk or the white of 

 the unincubated egg. 



Since we are here maintaining the view that embryological 

 development and differentiation, in common with other life proc- 

 esses, are directed by what may be called a material entelechy 



* Blastoderm: The flat sheet formed by the embryo's cell-layers when cleavage is 

 discoidal (Needham). 



