THE MECHANISTIC CONCEPTION OF LIFE 159 



substances. Thus the same kind of reaction was observed to 

 occur both in organic and inorganic materials, and though we 

 still speak of enzyme action in relation to vital chemistry and 

 catalysis in regard to inorganic reactions, we know very well that 

 the two classes of chemical changes are of the same kind. 



Along with all this investigation went on the synthesis of 



/ " organic " substances by the chemists. It is almost possible, 

 even now, to feel the thrill that physiologists must have ex- 

 perienced in 1828 when Wohler synthesised urea from mineral 

 substances. Before then there was an apparently hard line 

 drawn between organic and inorganic chemical compounds, and 

 it was thought that there were many substances, such as urea, 

 starch, sugar, albumen, etc., which were only and could only be 

 found in the cells of a living plant or animal. Wohler's syn- 

 thesis of urea broke through that line, and the far more wonderful 

 syntheses of sugars and polypeptides (the constituents of proteids) 

 by Fischer and his pupils obliterated it altogether. To-day we 

 look forward with complete assurance to the time when starches, 



I proteids, and fats capable of assimilation by the animal body 

 will be prepared, from their elements, by the chemists. 



Finally (and now we come down to a relatively short time 

 ago), Jacques Loeb demonstrated the possibility of artificial 



I parthenogenesis, and thus physico-chemical mechanism seemed 

 to be attacking vitalism in the very citadel itself. Before these 

 famous experiments were made parthenogenesis (that is, virgin 

 generation) was known to occur in a very few of the lower 

 animals, but in most lower and all higher forms it was quite 

 unknown; the ovum formed by the female could only be made 

 to develop when it was impregnated, or fertilised, by the sper- 

 matozoon formed by the male, and apart from the latter there 

 could, apparently, be no reproduction. Now early in the 

 present century Loeb showed that by simply adding certain 

 chemical substances to the water containing the eggs of sea 

 urchins, the latter could be made to undergo normal develop- 

 ment. It is true that the male element in reproduction is not 

 replaced by a chemical substance, for the spermatozoon does 

 much more than simply initiate the process of segmentation and 

 development of the ovum : it adds the paternal characters to the 

 maternal ones. Still, even the initiation of the process of 

 development by a simple mineral salt is a result of the most 

 extraordinary theoretical interest. 



