ii CHANGE OF FORM IN MUSCLE DURING ACTIVITY 169 



Seeing that mechanical excitation of the muscular coat 

 produces contraction, when applied to any point of the ureter, 

 which proceeds from either side of the excited spot with a 

 rapidity a thousand times less than the velocity of excitation in 

 nerve ; and further, that peristaltic and anti-peristaltic propa- 

 gation of the movement are exhibited in all parts of the ureter 

 after excision, only one view, as Engelmann stated, is admissible : 

 the peristaltic and anti-peristaltic propagation of the movement is 

 due to the fact that excitation is transmitted directly from cell to 

 cell in the muscle without intervention of ganglion-cells or nerve-fibres. 

 In other words : the ureter in its normal state is physiologically a 

 single, hollow, organic muscle-fibre. Eecent investigations into the 

 anatomical connections of smooth muscle-cells give consistent sup- 

 port to this view, inasmuch as they indicate continuity at least of 

 the sarcoplasm, if not of the fibrils also. But the first is sufficient if, 

 we can hardly doubt, the sarcoplasm can transmit excitation from 

 fibril to fibril. " Plasma bridges " indeed become superfluous, since, 

 as Engelmann correctly observes, there is nothing to prevent such 

 close contact of the naked, sheathless, living fibre-cells, that they 

 form a physiological continuity. This, however, admits that 

 a molecular effect may propagate itself in the ureter in all 

 directions from its point of origin. Similarly, of course, we may 

 imagine the process of conductivity within the plexus of the 

 striated muscle-cells. In these parts consisting of smooth, or 

 striated, uninuclear muscle -cells we are dealing with an 

 organisation of cells, each individual of which is similarly 

 co-ordinated in function, like the other excitable cell-aggregates 

 of plants and animals with which we are acquainted. Indeed, 

 we are reminded almost involuntarily of the co-ordinated activity 

 of ciliated cells, which can be shown experimentally to stand in 

 close internal relations of conductivity, although the individual 

 elements appear anatomically to be even more distinct than the 

 cells of smooth muscle. Here, at all events, no protoplasmic 

 bridges have been demonstrated, although they unquestionably 

 exist in many smooth muscles, as well as in excitable vege- 

 table-tissues. It appears, however, that in all such cases of 

 " cell-conductivity " the transmission of excitation is much more 

 liable to be disturbed, and is in a much higher degree dependent 

 upon external and internal conditions, than within one and the 

 same cell-body. Doubtless in the last resort this is the reason why 



