66 



VETERINARY PHYSIOLOGY 



FIG. 31. Respiration of muscle in a closed 

 chamber. 



up oxygen from the air round about it, and constantly gives 

 off carbon dioxide. In contracting, more carbon dioxide is 

 given off, and usually the amount of oxygen taken up is also 

 increased (fig. 31). 



Here we have at once evidence that muscle breathes, and 

 that this process of respiration is increased during muscular 

 activity. The affinity of muscle for oxygen is very great, so 



great that it can actually 

 take oxygen out of chemical 

 combinations. If alizarin 

 blue be injected into the vein 

 of an animal, the blood be- 

 comes blue, but the muscles 

 remain colourless, having 

 reduced the pigment to a 

 colourless condition. When 

 freely exposed to air after 

 death, the blue colour re- 

 turns. 



3. Changes in the Blood passing through Muscle. For the 

 investigation of this the hind legs of a dog have been used. 

 The blood going to one leg, and the blood coming from the 

 other, are collected at the same time. It is found that the 

 blood in passing through the muscles has gained carbon dioxide 

 and lost oxygen. If the muscles be kept contracted, it is 

 further ascertained that the amount of carbon dioxide gained 

 is increased, while usually the amount of oxygen taken up 

 is also increased. This observation confirms the investiga- 

 tions on the changes in the air surrounding a muscle. 



But the solid constituents of the blood are also changed. If 

 the muscles have been contracting, the blood is found to 

 contain sarcolactic acid probably combined with ammonia. 



We shall afterwards find that blood contains small quantities 

 of glucose, C 6 H 12 6 . As it passes through muscle it loses some 

 of this, even when the muscle is at rest, and a much larger 

 amount when the muscle has been active. 



The changes in the proteins of the blood going to and coming 

 from muscle have not been properly investigated. 



Some observers have obtained results which seem to indicate 

 that the amount of fat which is found in the blood is 



