OXIDATION AND REDUCTION 593 



mention here. Mammalian liver was rubbed with sand, water added, and the 

 mixture centrifuged for ten minutes. A suspension of fine particles was obtained, 

 which absorbed oxygen and gave off carbon dioxide, thus confirming certain 

 statements of Battelli and Stern with respect to " water-soluble respiration." The 

 amount of oxygen consumed was about one-fifth of that consumed by the intact 

 liver in an equal time. The remaining four-fifths are what Battelli and Stern call 

 the "chief respiration" (1909). The particles were small enough to show Brownian 

 movements, but were removed by filtration through a Berkefeld filter. No doubt 

 they would be removed by the Buchner method in Harden and Maclean's work. 

 The Berkefeld filtrate certainly showed a slight oxygen consumption, about one- 

 twenty-fifth of that of the entire liver, but there might have been a few ultra- 

 microscopic particles present. . 



ENERGETICS OF OXIDATION IN CELLS 



As frequently pointed out already, the energy required for the various purposes 

 of the organism is derived, except in very special cases, entirely from oxidation. 

 The necessity of considerable combustion in muscle cells doing external work is 

 clear, as also where gland cells are performing osmotic work. But, as Warburg 

 points out (1914, pp. 256-258), the high oxygen consumption of nucleated blood 

 corpuscles, of the central nervous system and of the developing egg, is difficult to 

 understand, since there is no apparent work done, with the exception of a minimal 

 amount. This is especially noticeable in the last case referred to, since the rate of 

 oxidation has no relation even to the morphological changes taking place. What 

 then becomes of the energy ? It would seem wasteful if it were merely degraded 

 to heat. Warburg, therefore, makes the suggestion already referred to, that there 

 may be work done in a way that is invisible, but yet indispensable. It may be 

 required to maintain the " structure " of the cell, in the sense of preventing the 

 mixing of constituents by diffusion, in maintaining intact certain properties of 

 the semipermeable membranes, such as electric charge, or possibly irreciprocal 

 permeability and other states of which we have, at present, little knowledge. 



The relation of oxygen to the work of the muscle cell has been given in some 

 detail above (page 446), arid reference also made to the work of secretion and so on. 

 In the present place, some interesting investigations, chiefly by Meyerhof, on the 

 total energy changes of certain isolated cells, as indicated by heat production, 

 may be referred to. 



Experiments on whole organisms, such as those done by Rubner, Benedict, 

 Macdonald, etc., show that the heat production is practically identical with the 

 loss of chemical energy of the food-stuffs. Bohr and Hasselbalch (1903) determined 

 the heat production of the developing chick, comparing it with the respiratory 

 exchange, and found it to be identical with that of fat, as indicated by the 

 respiratory quotient. The fact is interesting as showing that the formation of 

 the morphological structures which contain nitrogen uses up no measurable amount 

 of energy. 



The experiments, of Meyerhof (1911) were concerned with the developing eggs 

 of the sea urchin. The "caloric quotient" was first determined. This is the 

 number expressing the amount of heat formed, in gram-calories, per milligram of 

 oxygen consumed. Previous workers, Zuntz, Pfliiger, Rubner, found this number to 

 be, neglecting the second decimal place, when protein is burnt, 3'2 ; when fat, 3 '3 ; 

 when carbohydrate, 3*4 to 3 - 5. Now that of the developing egg is between 2'55 

 and 2 -9. This number is made slightly lower if the heat of solution of carbon 

 dioxide and that of its combination to sodium bicarbonate is taken into account. 

 This value, moreover, remains the same, whether fertilised or unfertilised eggs 

 are taken, or if cell division is prevented by the presence of phenyl-urethane, as in 

 Warburg's experiments. If work had been done in formation of coarse morpho- 

 logical structures, it is plain that the values could not be the same in these different 

 cases. 



It will be remembered that Warburg showed that ammonia, which enters the 

 cells, stops cell division, but increases slightly the oxygen consumption. Now 



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