A STUDY OF THE MUSCLES 



199 



and when the gelatin cools, the network of blood vessels can 

 be traced to the fine capillaries that run around the smaller 

 muscle bundles. A microscop- 

 ical preparation shows still finer 

 branches between the individual 

 fibers. From the lymph that 

 comes from these microscopic 

 tubes, each muscle fiber takes the 

 all-important proteid, the sugar, 

 fat, and water, and to the lymph in 

 exchange are given the waste car- 

 bon dioxid, water, and urea pro- 

 duced during muscular activity. 



Nerve Supply to Muscles. Much 

 of the wonderful progress in micro- 

 scopical work that has been made 

 in recent years, has been due to 

 discoveries in methods of staining. 

 Several chemical mixtures are now ? ^ 1 11 



known which, if applied to muscle, 

 will stain nerve tissue in such a 

 way that it can be readily dis- 

 tinguished from every other kind 

 of tissue. Hence in microscopical 

 preparations, it is possible to trace 

 the minute branches of a nerve 

 from the brain or spinal cord, 

 through the muscle bundles, to 

 their endings on the muscle fibers. 



FIG. 



in 



We see, therefore, that the ner- 

 vous system controls the action 

 not only of a whole voluntary 

 muscle, but also of each individual 

 muscle fiber. 



Standing. Although to most 

 of us it seems an easy matter 



93. Muscles used 

 standing erect. 



I = muscles back of calf. 



1 = muscles front of calf. 



II = muscles back of thigh. 



2 = muscles front of thigh. 

 Ill = muscles of spine. 



3 = muscles of abdominal 



wall. 

 4, 5 = muscles of front of 



neck. 

 Arrows indicate direction of 



action of muscles. 



