NOTES AND ADDITIONS. 301 



other. If resistance to transmission can be shown, then the 

 irritation cannot increase in strength during its propagation 

 through the nerve. I will, therefore, here briefly mention 

 the reasons which induce me to declare in favour of one, and 

 against the other, of these assumptions. 



As is mentioned on p. 141, transmission becomes con- 

 siderably harder when the nerve is in an anelectrotonic 

 condition, and in strong anelectrotonus it is even rendered 

 altogether impossible. It is natural to regard this greater 

 difficulty as an increase of a resistance already present. A 

 more important reason is however to be found in the phe- 

 nomena which occur in reflex actions. If a sensory nerve 

 is irritated, the excitement can be transmitted to the dorsal 

 marrow and the brain, where it may be transferred to a 

 motor nerve (of. p. 274). This transference always occupies 

 a considerable time, which I call reflex-time. If a sensory 

 nerve is irritated sufficiently to cause a powerful reflex action 

 (called a 'sufficient irritant'), if the reflex-time in this case is 

 determined, and if irritants of continually increasing strength 

 are then allowed to act on the same point in the nerve, 

 then the reflex-time is found to become continually shorter. 

 If, however, a point in the nerve lying very near the dorsal 

 marrow is irritated, then even in the case of a 'sufficient 

 irritant ' the reflex-time is short. It is evident that the 

 duration of the reflex-time depends on the strength of the 

 irritant when it reaches the dorsal marrow. The irritant 

 which comes from the point in the nerve adjacent to the 

 dorsal marrow is but slightly affected; but that coming 

 from a more remote point is weakened ; so that a much 

 stronger irritant must be applied to these more remote points, 

 if an equally short reflex- time is to be attained. 



It is true that these observations have been made with 

 sensory nerves. But owing to the entirely similar character 

 exhibited by all kinds of nerve-fibres in all points, where 

 comparison is possible, we are justified in applying the views 

 thus gained to the motor-nerves. It is, at all events, im- 



