264 A MANUAL OF PHYSIOLOGY 



for the carbon dioxide given off were 0*0058 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 experiments were performed under 

 conditions so normal that the animal continued to eat its hay 

 with seeming unconcern throughout the observations, although 

 these involved the exposure of the main bloodvessels of the 

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



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 during active secretion (Barcroft) . 



Nature of ihe Oxidative Process. When we have recognised 

 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 demonstrat- 

 ing the existence in the tissues of oxidizing ferments or oxy- 

 dases. 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 in- 

 stances of its action in connection with the oxidation of the 

 guaiaconic acid in tincture of guaiacum in the presence of the 

 peroxide (p. 69). As regards the activity of this ferment, blood 

 comes first ; then follow spleen, liver, pancreas, thymus, brain, 

 muscle, 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 oxidation of 

 guaiaconic acid in the presence of atmospheric oxygen, and 

 these do not need peroxide of hydrogen in order to render guaia- 

 cum blue. An allied ferment which also induces the blue colour 

 in tincture of guaiacum is the so-called laccase found in the most 



