RECENT DEVELOPMENT OF BIOLOGY 15 



any concentration with the same ease and certainty as for any other 

 chemical reaction. 



We know as yet but little concerning the method by which enzymes 

 produce their accelerating effects. It seems that the facts recently 

 gathered speak in favor of the idea of intermediary reactions. Ac- 

 cording to this idea the catalyzers participate in the reaction, but 

 form combinations that are again rapidly decomposed. This makes 

 it intelligible that at the end of the reaction the enzmes and cataly- 

 zers are generally in the same condition as at the beginning of the 

 reaction, and that a comparatively small quantity of the catalyzer 

 is sufficient for the transformation of large quantities of the reacting 

 substances. 



This chapter should not be concluded without mentioning the 

 discovery of zymase by Buchner. It had long been argued that only 

 certain of the fermentative actions of yeast depended on the presence 

 of enzymes which could be separated from the living cells, but that 

 the alcoholic fermentation of sugar by yeast was inseparably linked 

 together with the life of the cell. Buchner showed that the enzyme 

 which accelerates the alcoholic fermentation of sugar can also be 

 separated from the living cell, with this purely technical difference 

 only, that it requires a much higher pressure to extract zymase 

 than any other enzymes from the yeast cell. 



III. Physical Structure of Living Matter 



We have stated that living organisms are chemical machines 

 whose framework is formed by colloidal material consisting of 

 proteins, fatty compounds, and carbohydrates. These colloids 

 possess physical qualities which are believed to play a great role in 

 life phenomena. Among these qualities are the slow rate of diffusion, 

 the existence of a double layer of electricity at the surface of the 

 dissolved or suspended colloidal particles, and the production of 

 definite structures when they are precipitated. We may consider it 

 as probable that the cytological and histological structures of living 

 matter will be reduced to the physical qualities of the colloids. But, 

 inasmuch as the physics of the colloids is still in its beginning, we 

 must not be surprised that the biological application of its results 

 is still in the stage of mere suggestions. The most important result 

 which has thus far been accomplished through the application of 

 the physics of colloids to biology is Traube's invention of the semi- 

 permeable membranes. To Traube we owe the discovery that every 

 living cell behaves as if it were surrounded with a surface film which 

 does not possess equal permeability for w T ater and the substances 

 dissolved in it. Salts which are dissolved in water, as a rule, migrate 

 much more slowly into the living cells than water. This discovery 



