244 A Manual of Veterinary Physiology. 



of repair. We have to learn, therefore, the nature of 

 the waste and repair occurring in muscles, and the physical 

 and electrical phenomena exhibited by muscular tissue 

 during the period of rest and activity. 



The oxygen carried to muscles by the blood is absorbed 

 by them in considerable quantities, and a volume of car- 

 bonic acid, in less quantities than corresponds to the 

 oxygen absorbed, is returned to the venous blood. 

 Whether a muscle be at rest or active, it is always absorb- 

 ing O and giving up C0 2 , and, moreover, it is always storing 

 up oxygen. The absolute amount of stored up and 

 COo produced varies considerably in rest and work, being 

 much greater during the latter than during the former 

 condition. 



In an active muscle the bloodvessels are more dilated 

 than in the muscle of rest, and this dilatation corresponds 

 to the increased quantity of blood sent to the part, by 

 which alone the irritability of the muscle, or its power of 

 contraction, is maintained; whatever leads to a smaller 

 quantity of blood being sent to an active muscle, produces 

 partial or complete paralysis of the group or groups of 

 muscles affected. This is well seen in the horse when 

 suffering from embolism of the iliac arteries and may 

 readily be produced in the rabbit by compressing the 

 aorta. 



Muscles in a state of activity contain less glycogen and 

 sugar than those in a state of rest, due to the amount 

 utilized during muscular activity. But glycogen is not 

 necessarily the source of the energy, since muscles free 

 from glycogen can work normally. Glycogen is rather ;. 

 convenient accessory than a necessary factor in the pro- 

 duction of energy in a muscle. 



Active muscles present an acid reaction due to the 

 formation of sarcolactic acid, while the resting muscle is 

 alkaline. 



During muscular activity heat is produced, the blood 

 returning from the muscle having a higher temperature 

 than that which supplies it. The amount o[' heat evolved 



