PECULIARITIES OF MUSCLE TISSUE 67 



therefore, must give rise to a loss of stimulation and tonus. Afferent 

 impulses may come from the skin and subcutaneous tissue as well as 

 from the muscles themselves; in fact, they may also arise in higher 

 centers. Concerning those arising in the muscles themselves, it may 

 be stated at this time that the division of the afferent path of a muscle, 

 or groups of muscles, is generally followed by a considerable loss of 

 their tonus. It seems, therefore, that the so-called muscle-sense has 

 much to do with this phenomenon. The pressure exerted by the con- 

 tracting fibers upon the muscle-spindles, sets up certain afferent im- 

 pulses which are eventually relayet . he effector, and keep the latter 

 in a condition of functional alertnes^s. In last analysis, therefore, the 

 tonus of muscle must be regarded as a reflex phenomenon. 



The Trophic State of Muscle. — The anatomical and functional 

 integrity of a muscle can only be retained if it is subjected to frequently 

 repeated stimulations. In case the latter cease at any time, say, in 

 consequence of the severance of the path by means of which the mus- 

 cle is connected with the central nervous system, it undergoes retro- 

 gressive changes and finally loses its functional usefulness entirely. 

 This atrophic state is ushered in by a diminution in its irritability, 

 lasting a number of days. Subsequent to this period its irritability 

 again increases and remains high for several weeks until it is abolished 

 altogether. During the second* phase the muscle is prone to exhibit 

 irregular contractions which remain confined to certain groups of its 

 fibers and impart a peculiar fibrillary motion to its substance as a 

 whole. Peculiarly enough, this degeneration may be arrested at any 

 time by reuniting the ends of the cut nerve. The muscle then grad- 

 ually recovers and regains its normal trophic condition in the course 

 of time. During the interim the muscle may in a measure be pre- 

 vented from losing its function altogether by stimulating it artifically 

 through the integument. 



It must be evident, therefore, that the metabolism of a muscle is 

 absolutely dependent upon its connection with the central nervous 

 system. For this reason, it is commonly held that the ganglion cells 

 exert a trophic influence upon the muscle, which, however, is brought to 

 bear upon it through its ordinary motor nerve and not through special 

 trophic fibers. Hence, any motor nerve may be said to possess trophic 

 qualities, because it keeps the muscle in activity, thereby favoring its 

 metabolic processes. The blood supply is, of course, of some impor- 

 tance, because a copious flushing out of the muscle retards the process 

 of degeneration, while a scanty blood supply greatly favors the occur- 

 rence of these changes. This fact is demonstrated in a convincing 

 manner by Stenson's experiment. If the abdominal aorta of a rabbit 

 is Ugated, the muscles of the posterior extremity soon lose their irri- 

 tability, owing to the decrease in the supply of oxygen and other 

 nutritive material. Upon releasing the compression their func- 

 tion reappears very quickly. The same results may be obtained 

 by perfusing them with venous blood or by retarding the flow 



