PROTOPLASM AS A PHYSICAL SYSTEM 55 



and inorganic salts the various special compounds, 

 definite and constant in number, proportions, and 

 distribution, which compose the yeast protoplasm. 



Some of the changes in the chemical reactivity of 

 protoplasm resulting from mechanical or other destruc- 

 tion of the living cells or tissue are well illustrated by 

 Fletcher's and Hopkins' work on the formation and 

 disappearance of lactic acid in muscle;^ also by the work 

 of Harden and Maclean on oxidation by isolated animal 

 tissues f and more recently by Warburg's determinations 

 of the oxygen consumption in living cells (sea-urchin 

 eggs, blood corpuscles, bacteria, etc.) as compared with 

 that of the same cells after death or fine mechanical 

 subdivision.^ In all of these cases chemical activity 

 is greatly decreased when the protoplasmic structure is 

 artificially destroyed. Warburg has also shown that 

 when certain cells, the blood corpuscles of birds, are 

 mechanically broken down by freezing and thawing, 

 the oxygen consumption exhibited by the residue is 

 associated with the more solid part of the complex — that 

 which can be separated by centrifuging ; similarly, in 

 liver cells the separable granules have a relatively high 

 oxygen consumption."* A relation of oxidative activity 

 to the solid part of the protoplasmic structure is thus 

 indicated. In some cases it can be shown micro- 

 chemically that certain oxidations (the indophenol 

 reaction) occur most actively at the surfaces of solid 



^ Fletcher and Hopkins, Journal of Physiology, XXXV (1907), 247. 

 * Harden and Maclean, Journal of Physiology, XLIII (1911), 34. 



3 Warburg, Ergebnisse der Physiol., XIV (1914), 253. 



4 Warburg, cf. Biochem. Zeitschrift, CXIX (1921), 134, and references 

 to earlier papers there given. 



