584 ON THE SCIENCE OF EASY CHAIKS. 



entirely ceased to respond to a stimulus. He then washed out 

 the waste products from it by means of a little salt and water, 

 and found that its contractile power again returned, just as the 

 power of the steam-engine would be increased by raking the 

 ashes which were blocking up the furnace and putting out the 

 iire. These waste products are partly removed from the muscles 

 hj the blood which flows through them, and are carried by 

 ithe veins into the general circulation. There they undergo 

 inore complete combustion, and tend to keep up the tempera- 

 ture of the body. At the same time, however, according to 

 Preyer, they lessen the activity of the nervous system, pro- 

 •ducing a tendency to sleep, and in this way he would, at least 

 to some extent, explain the agreeable drowsiness which comes 

 on after muscular exertion. It would seem, however, that the 

 circulation of the blood is insufficient to remove all the waste 

 products from the muscles, for we find that they are supplied 

 with a special apparatus for this purpose. Each muscle is 

 generally ensheathed in a thin membrane, or fascia, and besides 

 these we have thicker fascise ensheathing whole limbs. These 

 fascia act as a pumping apparatus, by which the products of 

 waste may be removed from the muscles which they invest. 

 They consist of two layers, with spaces between. When the 

 muscle is at rest these layers separate, and the spaces become 

 filled with fluid derived from the muscle, and when the muscle 

 'Contracts it presses the two layers of its investing sheath 

 together, and drives out the fluid contained between them. 

 'This passes onwards into the lymphatics, where a series of 

 valves prevent its return, and allow it only to move onwards, 

 till at last it is emptied into the general circulation. 



In strong and healthy people the veins and lymphatics 

 together are quite able to take up all the fluid which the 

 arteries have supplied to the muscles, and thus prevent any 

 accumulation from taking place either in them or in the cellular 

 tissue adjoining them, or at least prevent any such accumula- 

 tion as might become evident to the eye. In delicate, weakly 

 persons, or in those who suffer from certain diseases of the 

 vascular system, this is not the case ; and after standing or 

 walking for a long time the legs become swollen, so that the 



