168 ELECTRO-PHYSIOLOGY CHAP. 



at a longer interval ; as is naturally still more easy to demonstrate 

 with artificially excited waves of contraction. It is evident that 

 immediately after the passage of a wave of contraction, the con- 

 ductivity is entirely abolished, and only recovers its original 

 proportions a comparatively long time after. In the rabbit the 

 first stage lasts for over a second under normal conditions, and 

 with diminution of excitability may be prolonged to 5, 10, or 

 15 sees. With normal conditions, normal conductivity is re- 

 established, at most, 1 sees, after the passage of a contraction. 



The slowness of the entire process of excitation constitutes an 

 easy and, we may say, direct means of determining the length of 

 the contraction wave in the ureter, if the approximate duration 

 of the contraction is multiplied by its velocity. If we reckon the 

 first at about ^ sec., the other at 33 mm., the wave-length comes 

 out at 1 cm., a value which is tolerably constant, since we find 

 experimentally that the alterations in duration of contraction are, 

 within a wide range, inversely proportional with the simultaneous 

 alterations in the rate of conductivity. These results tally with 

 direct observation, since the length of the contraction wave can 

 be immediately determined on the exposed ureter. 



On a ureter that is free from fat and somewhat hypenemic, 

 it is easily seen that with each contraction a strip of about 1 

 cm. long becomes pale in toto, and progresses in undulations 

 with the constriction. The pallor is generally most marked at 

 the middle of the strip, the ureter sometimes appearing almost 

 white ; the normal gray-pink colour then returns by degrees on 

 either side. If anything may be concluded from this as to the 

 magnitude of contraction in the single cross-sections, it would 

 follow that shortening and relaxation of the muscle-substance of 

 the ureter proceed with equal velocity (Engehnann). 



It will be seen from the above that a whole series of 

 facts bearing on the relations and conduction of the contraction 

 process may be immediately demonstrated on the part in, question, 

 while in striated muscle the finest artificial means have to lie 

 employed for their detection a point which we shall have to 

 insist on later. For the moment we need only refer to the 

 weighty question as to the manner in which the conductivity 

 of excitation (contraction) is effected in the organ- -which is 

 composed of innumerable individual cells united by cement - 

 substance. 



