i88 THE POPULAR SCIENCE MONTHLY. 



greater and greater, tlie tendency is to assume the position of the N 

 with the limbs at a more or less obtuse angle, but when sitting in an 

 ordinary chair we find relief from raising the feet by means of a foot- 

 stool, although this tends to make the angles of the N more acute in- 

 stead of more obtuse. Still more relief, however, do we obtain when 

 the legs are raised up on a level with the body by being placed upon 

 another chair, or by being rested on the Indian bamboo seat already 

 described. If, in addition to this, the legs are gently shampooed up- 

 ward, the sensation is perfectly delightful, and the feelings of fatigue 

 are greatly lessened. To understand how this can be, it is necessary 

 for us to have some idea as to the cause of fatigue. Any muscular 

 exertion can be performed for a considerable time by a man in average 

 health, without the least feeling of fatigue, but by-and-by the muscles 

 become weary, and do not respond to the will of their owner so read- 

 ily as before ; and, if the exertion be too great, or be continued for 

 too long a time, they will ultimately entirely refuse to perform their 

 functions. The muscle, like a steam-engine, derives the energy which 

 it expends in mechanical work from the combustion going on within it, 

 and this combustion, in both cases, would come to a standstill if its 

 waste products or ashes were not removed. It is these waste products 

 of the muscle which, accumulating within it, cause fatigue, and ulti- 

 mately paralyze it. This has been very neatly shown by Kronecker, 

 who caused a frog's muscle, separated from the body, to contract until 

 it 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 block- 

 ing up the furnace and putting out the fire. These waste products are 

 partly removed from the muscles by the blood which flows through 

 them, and are carried by the veins into the general circulation. There 

 they undergo more complete combustion, and tend to keep up the tem- 

 perature of the body. At the same time, however, according to Preyer, 

 they lessen the activity of the nervous system, producing 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 insheathed in a thin membrane, or fascia, and besides these 

 we have thicker fascige insheathino- 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 



