PROTOPLASM 29 



is also evidence that water is necessary to that most fundamental of vital 

 processes, oxidation. The importance of these and other characteristics 

 of water is discussed at length by Henderson in his inquiry into the 

 biological significance of the properties of water. 



Another highly important chemical feature of protoplasm is its 

 hydrogen-ion concentration. Through the use of color indicators and 

 the microinjection method Chambers and his associates^ have determined 

 the pH of a number of animal cells with considerable accuracy. They 

 find the nucleus to be slightly alkaline (pH about 7.5 to 7.6) and the 

 cytoplasm slightly acid (pH about 6.7 to 6.9).^° Injury causes the cyto- 

 plasm to become much more acid (pH 5.2 to 5.5). If the pH remains 

 altered, the cell dies. The experiments show the protoplasm to be well 

 "buffered," or protected against sudden or radical alterations in pH, by 

 certain substances in solution. The principal buffers in organisms are 

 carbonates, bicarbonates, and phosphates. It is a very significant fact 

 that the vital reactions occur in a medium near the point of neutrality, and 

 that protoplasm has a means of preserving its pH at the proper level under 

 a considerable range of environmental conditions. 



The pH values for plant protoplasm are less well known, since the 

 analyses have included considerable amounts of cell sap, which in mature 

 cells is usually decidedly acid in reaction. As a result, the published 

 values^^ in nearly all cases fall well on the acid side of neutrality. More- 

 over, in determinations made on expressed saps an increase of acidity due 

 to injury is suspected. 



Active acidity, due to the concentration of free hydrogen ions, is to 

 be distinguished from potential acidity, which is determined by the quan- 

 tity of hydrogen ions which can be made to combine with a base. The 

 nucleus, although slightly alkaline to indicators, has a large amount of 

 undissociated nucleic acid which reacts strongly with basic dyes in the 

 usual staining procedures; hence the common statement that the nucleus 

 reacts as an acid. In general the cytoplasm has a high potential alka- 

 linity and a slight active acidity. 



Protoplasm, because of the many combinations possible among its 

 numerous constituents, is a substance which may exist in a vast number of 

 different forms. When it is further recalled that many of the constituents 



» Chambers (1928, 1930(7, 1932), Chambers and Pollack (1927), Chambers, 

 Pollack and Hiller (1927), Chambers, Pollack and Cohen (1929), Reznikoff and 

 Pollack (1928), Pollack (1928), Chambers and Cameron (1932), Chambers and Kerr 

 (1932). 



^^ The reactions of solutions ranging from 0. 1 normal in terms of hydrogen ions 

 to lO"!* normal are expressed in 14 steps from /jH 1 to jiH 14. The neutral point is 

 at pH 7; a solution with a lower p^ is acid, while one with a higher pH is alkaline. 

 The scale is a logarithmic one, a decrease of 1 in /jH corresponding to a tenfold increase 

 in hydrogen-ion concentration. See Gortner (1929, p. 92). 



" Eichhorn (1927) and Small (1929) review the data for plant tissues. See the 

 papers of Pfeiffer (1930, 1931, 1932) on the isoelectric point. 



