Decembek 9, 1904.] 



SCIENCE. 



779 



posed. This makes it intelligible that at 

 the end of the reaction the enzymes and 

 catalyzers are generally in the same condi- 

 tion as at the beginning of the reaction, 

 and that a comparatively small quantity 

 of the catalyzer is sufficient for the trans- 

 formation of large quantities of the react- 

 ing 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 fermenta- 

 tive actions of yeast depended on the 

 presence of enzymes which could be sepa- 

 rated 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 sepa- 

 rated 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. 



PJQYSICAL STRUCTURE OP LIVING MATTER. 



We have stated that living organisms 

 are chemical machines whose framework is 

 formed by colloidal material consisting of 

 proteins, fatty compounds, and carbohy- 

 drates. 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 precipi- 

 tated. We may consider it as probable 

 that the cytological and histological struc- 

 tures of living matter will be reduced to 

 the physical qualities of the eoUoids. But, 

 , inasmuch as the physics of the colloids is 

 still in its beginning, we must not be sur- 

 prised that the biological application of 



its results is still in the stage of mere sug- 

 gestions. The most important result which 

 lias thus far been accomplished through 

 the application of the physics of colloids 

 to biology is Traube's invention of the 

 semipermeable 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 water 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 of the semi-permeability of the 

 surface films of living protoplasm made, 

 it possible to recognize the variable which 

 determines the exchange of liquids between 

 protoplasm and the liquid medium by 

 ■which it is surrounded, namely, the osmotic 

 pressure. Inasmuch as the osmotic pres- 

 sure is measurable, this field of biology has 

 entered upon a stage where every hypoth- 

 esis can be tested exactly and biology is 

 no longer compelled to carry a ballast of 

 shallow phrases. We are now able to 

 analyze quantitatively such functions as 

 lymph formation and the secretion of 

 glands. 



Eecent investigations have thrown some 

 light on the nature of the conditions which 

 seem to determine the semi-permeability of 

 living matter. Quincke had already men- 

 tioned that a film of oil acts like a semi- 

 permeable membrane. From certain con- 

 siderations of surface tension and surface 

 energy it follows that every particle of 

 protoplasm which is surrounded by a 

 watery liquid must form an extremely 

 thin fibn of oil at its surface. Overton 

 has recently shown that of all dissolved 

 substances those Avhieh possess a high solu- 

 bility in fat, e. g., alcohol, ether, chloro- 

 form, diffuse most easily into living cells. 

 Overton concludes that lipoid substances 

 such as lecithin and cholesterin which are 

 found in every cell determine the phenom- 



