GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 83 



muscle does not contract so quickly if it be excited through its nerve as when 

 stimulated directly. Part of the lost time is spent in transmission of the 

 excitation through the nerve ; but after allowance has been made for this loss 

 there is a balance to be accounted for, and this is credited to the motor end- 

 organ. The time used by the motor end-plate is found to be 0.0032 second. 1 



Motor end-organs are, as we have seen, poisoned by curara (see p. 26) and 

 a number of other drugs which have little influence on the rest of the axone 

 or on the muscle. 



If a muscle is continuously excited for a considerable time by irritants 

 applied to its nerve, it will at last cease to contract. Direct excitation shows 

 that, though weakened, it is still capable of contraction, and we know that 

 the nerve-fibre does not fatigue. The cessation of contraction is due to 

 fatigue of the motor ends. 



The motor end-organ is found to lose its vitality quicker than the muscle 

 or the nerve-fibre, if it be deprived of its normal blood-supply. 



If a motor nerve be cut, the part of the axone separated from the body of 

 the nerve-cell and the terminal organ degenerates, but the degeneration proc- 

 ess stops at the muscle. 



These facts show that the motor end-organ differs physiologically in many 

 respects from the rest of the axone and from the muscle. Moreover, they 

 favor the idea that excitation is not conducted directly from nerve to muscle 

 protoplasm. That this is the case is also made probable by the fact that though 

 a condition of excitation is transmitted in both directions through nerve and 

 muscle protoplasm as long as there is continuity, a condition of excitation in 

 muscle substance does not appear to be transmitted to the motor nerve. Ap- 

 parently the protoplasm of the end-organ and the muscle are in contact, but 

 are not physiologically continuous, and excitation of muscle protoplasm by the 

 end-organ occurs through some special process. Various views have been 

 advanced with reference to the probable nature of such a process, but as no 

 one of them has received general acceptance they need not be dwelt upon here. 

 One point more, of interest in this connection, is the fact thai it is the sarco- 

 plasma rather than the fibrillary elements of the muscle that conies in contact 

 with the nerve end-organ, which would seem to show that this substance is 

 capable of being excited and conducting the excitation. If this be true of 

 muscle substance, it is likely that the semi-fluid part of the protoplasm of the 

 nerve, as well as perhaps the fibrillary part, may have the power of conduction. 



As a result of a series of* remarkable histological investigations on the 

 anatomy of the nervous system, the view has come to be generally accepted, 

 that the afferent nerve-fibres entering the spinal cord do not communicate 

 directly with the nerve-cells, but terminate in brush-like endings in close 

 contact with some part of the cells which they excite. A similar arrange- 

 ment has been found wherever nerve-cells are excited to action by nerve- 

 fibres. As in the case of the motor end-organ, it has remained a matter of 

 doubt whether the brush like ends of the axones should be considered to be 

 1 Bernstein: Arehiv fur Anatomic una Physiologie, 1882, S. 329. 



