84 POPULAR SCIENCE MONTHLY. 



evidence that the differences between muscular fibers, such as those of 

 the heart, which contract normally with what we call a spontaneous 

 beat, and the fibers of the skeletal muscles, which only, under ordinary 

 circumstances, contract when excited through their motor nerves, are 

 not so deep-seated as was at one time supposed, since the addition of 

 simple inorganic bodies to the living muscular substance, or their sub- 

 traction from it, can alter its behavior in this regard. The experi- 

 ments of Langendorff, Porter and others on the action of the isolated 

 hearts of warm-blooded animals, which, after being cut out of the 

 body, can be kept alive for several hours by feeding them through 

 their arteries with warm blood from a reservoir, have strengthened the 

 belief that the essential cause of the heart-beat is to be sought in the 

 muscular fibers and not in the nerve-cells present in certain portions of 

 the organ. 



With respect to the nerve-cell, research is at present largely con- 

 centrated upon the study of its minute structure. Among the numer- 

 ous methods of staining employed for this purpose two deserve espe- 

 cial mention: the method of Golgi, which is peculiarly useful for bring- 

 ing out the processes or branches of nerve-cells, and the method of 

 Nissl, which is of great service in the investigation of the body of the 

 cell. A typical nerve-cell when impregnated with a salt of silver, 

 according to Golgi's method, exhibits a wonderful profusion of bifur- 

 cating processes, picked out in black like the sharply shadowed branches 

 of a leafless tree under an electric light. But, however intricately the 

 branches of neighboring cells may mingle and intertwine, they do not 

 in general run into, or fuse with, each other, any more than the inter- 

 locking boughs of neighboring trees in a forest. By demonstrating this 

 important fact the method of Golgi has revolutionized our ideas of the 

 architecture of the nervous system. 



The significance of the peculiar angular or spindle-shaped bodies 

 in the protoplasm of the nerve-cell, which have been revealed by Nissl's 

 method of staining with methylene-blue, is at present arousing the 

 greatest interest. That they have some important relation to the nutri- 

 tion of the cell seems evident. For when the latter is severed from that 

 one of its processes (the axone) which constitutes the essential part of 

 the nerve-fiber that springs from the cell, the Nissl bodies break up, 

 and either disappear or are dispersed in the form of very minute 

 granules of stainable material in the protoplasm. At the same time 

 the cell becomes swollen, its nucleus is displaced to one side, and 

 it may even atrophy entirely and disappear. As a rule, however, after 

 several months it recovers its normal structure. The administration of 

 considerable quantities of alcohol and other drugs causes a similar 

 effect on the Nissl bodies. It has been known for half a century that 

 the axone degenerates when cut off from the cell of which it is a process. 



