INTERNAL OR TISSUE RESPIRATION * 7 i 



ing considerable amounts of potential energy which (like the accu- 

 mulator) can be discharged by appropriate stimuli.' 



The respiration of muscles in situ can be studied by collecting 

 samples of the blood coming to and leaving them and analyzing the 

 gases. The mere difference of colour between the venous and 

 arterial blood of a muscle, or other active organ, is sufficient to show 

 that oxygen is taken up and carbon dioxide given out by it to the 

 blood. This is the case in muscle sat rest, and even in muscles 

 with artificial circulation after they have become inexcitable. In 

 active muscles more oxygen is used up and more carbon dioxide 

 produced than in the resting state. Chauveau and Kaufmann, in 

 their experiments on the levator labii superioris musck of the horse in 

 feeding, found that the consumption of oxygen and the production 

 of carbon dioxide might be many times as great in activity as in rest. 



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 1-7 in a third, snowing 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. 



By means of the modern technique permitting the use of small 

 quantities of blood for the gas analysis, similar experiments have been 

 performed on a muscle as small as the cat's gastrocnemius. In one 

 experiment it was found that as a result of stimulation of the sciatic 

 lasting about 25 seconds the intake of oxygen was increased for at least 

 220 seconds. In this time the muscle used up 0-75 c.c. of oxygen, as 

 compared with 0-26 c.c., which it would have consumed had it not been 

 stimulated (Verzar). 



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 



