INTERNAL OR TISSUE RESPIRATION 267 



Thus in one experiment the amount of oxygen taken in, expressed 

 in c.c. per gramme of muscle per minute, was 0-008 during rest, and 

 0-14 during work; the corresponding quantities for the carbon 

 dioxide given off were 0-006 and 0-18. The respiratory quotient 

 rose to 1-3 in two experiments, and even to 17 in a third, showing 

 that the increase in the production of carbon dioxide was relatively 

 greater than the increase in the intake of oxygen. These expert 

 ments were performed under conditions so normal that the animal 

 continued to eat its hay with seeming unconcern throughout the obser- 

 vations, although these involved the exposure of the main blood- 

 vessels of the muscle, and the collection of samples of blood from them. 



For skeletal muscle at rest, Barcroft gives 0*004 c.c. per gramme 

 per minute as the oxygen consumption; during maximal activity 

 twenty times as much (0-08 gramme). In the heart of a small dog 

 through which blood was pumped by a larger dog the oxygen intake 

 when the heart was beating feebly was, on the average, about 

 o-oi c.c. per gramme of heart-muscle per minute. When the heart 

 was caused to beat very strongly under the influence of adrenalin, 

 the oxygen intake rose in one case to 0-08, and in two others to 0-04. 

 In the resting pancreas the oxygen intake has been found to be 0-03 

 to 0-05 c.c. per gramme per minute; in the active pancreas, o-i c.c. 

 The corresponding number for the submaxillary gland at rest is 

 0-03, and in activity 0-09; for the kidney, 0-03 at rest or during 

 scanty secretion, and 0-07 or even 0-09 during active secretion. 



Nature of the Oxidative Process. When we have recognized the 

 cells as the seat of oxidation, the question immediately presents 

 itself, How do they accomplish the feat of burning such masses of 

 food substances as can only be rapidly oxidized in the laboratory 

 at the temperature of the body by the most energetic chemical 

 reagents ? The researches of late years have furnished a key to 

 the solution of this long-standing puzzle by demonstrating the 

 existence in the tissues of oxidizing ferments or oxydases. Of these, 

 one of the most widely distributed is a ferment which splits off 

 oxygen from hydrogen peroxide. Since any oxidation produced 

 is only secondary to this decomposition, ferments which decompose 

 hydrogen peroxide are often spoken of as catalases, to distinguish 

 them from the oxydases proper. A catalase is found in practically 

 all the tissues of the body, as well as in vegetable cells, and we have 

 already mentioned instances of its action in connection with the 

 oxidation of the guaiaconic acid in tincture of guaiacum in the 

 presence of the peroxide (p. 76). As regards the activity of this 

 ferment, blood comes first; then follow spleen, liver, pancreas, 

 thymus, brain, miiscIeT and ovary. It is present in the blood-free 

 organs as well as in the blood. Some tissues, both animal and 

 vegetable, contain a ferment, an oxydase, which causes the oxida- 

 tion of guaiaconic acid in the presence of atmospheric oxygen, and 



