92 RESPIRATION 



according to the degree of their antagonism : thus the normal 

 respiration rate of Aspergillus niger in a culture medium con- 

 taining 19 c.c. of *5M sodium chloride and I c.c. of *5M 

 calcium chloride is maintained although each of these salts in 

 these concentrations and acting alone will accelerate respira- 

 tion.* With regard to respiration, the chlorides of magnesium 

 and sodium, of sodium or potassium and calcium exhibit a 

 conspicuous antagonism, whilst the chlorides of magnesium and 

 calcium and of sodium and potassium are antagonistic only to 

 a slight degree. 



ACIDITY. The degree of acidity of the cell sap shows 

 much variation and is an expression of the physiological con- 

 dition and of particular metabolism. Thus the acidity of 

 anthocyanin containing leaves may be double that of green 

 leaves of the same species, the acidity of fleshy plants is greater 

 by night than by day. 



In particular cases the hydrogen ion concentration may 

 profoundly modify the respiration intensity ; Nitrosomonas, for 

 example, shows the greatest rate of respiration in a medium 

 in which the P H value is between 8-4 and 8 '8, beyond the 

 limits of P H 9*4 - 7'6 the process comes to a standstill.! In 

 Penicillium chrysogenum variations in the value of P H between 

 4 and 8 do not affect the normal rate of respiration, that is, the 

 rate at neutrality, P H = 7 ; an increase of the value to 8 '8 

 results in the respiration decreasing to 60 per cent of the 

 normal, at which level it remains ; a decrease, on the other 

 hand, in the value of P H to 2-65 causes a gradual rise in the 

 respiration rate followed by a gradual fall to the normal. At 

 P H i'io to 1-95 the preliminary rise, amounting to 20 per 

 cent, is followed by a fall to below normal. The depression 

 brought about by a concentration P H = I -95 or less is irrever- 

 sible, whilst the similar decrease effected by a P H value of 8 '8 

 is reversible, the respiration rate returning to normal after the 

 plant is placed in a neutral solution. In acid solutions there 

 is an increase in the production of carbon dioxide and a de- 

 crease in alkaline solutions, a phenomenon which may be 

 paralleled in the test-tube : a neutral solution of dextrose and 



* Gustavson : " Journ. Gen. Physiol,," 1919, 2, 217, 

 fMeyerhof: loc, cit f 



