234 



ELECTRO-PHYSIOLOGY 



CHAP. 



tractile substance (3). Of this the accompanying curve (Fig. 90) 

 gives sufficient evidence. As in cardiac muscle, the striking- 

 disparity of effect between the two directions of current immedi- 

 ately after the injury equalises itself by degrees, and at last 

 becomes imperceptible. The explanation here again must be 

 sought in the independent dying of each fibre-cell. 



If these conclusions from the adductor muscle of Anodonta 

 are in almost complete conformity with the polar effects of current 

 in striated skeletal and cardiac muscle, this is not equally true of 

 other parts composed of smooth fusiform cells, in which excita- 

 tion with the constant current provokes a series of manifestations 

 differing in many respects (at least at first sight) very widely, 



FIG. 90. Localisation of persistent closure contraction at the kathode (A") on exciting the 

 adductor muscle of Anodonta. S= closure ; = opening. 



and thus suggesting that the polar law of excitation may not be 

 rigidly applicable to all kinds of muscle (31). 



Within the integument of Holothuria, along the entire length 

 of the body, there is a beautiful series of longitudinal muscle- 

 bundles, with parallel fibres, in the form of five flat bands, com- 

 posed of solitary spindle-cells, pointed at either end, which, after 

 the animal (H. Poll) is opened, appear as pale, or pinkish, and 

 transparent striae. Many thinner and finer bands of circular 

 muscle run between each two longitudinal muscle-bands, form- 

 ing a complete investment of the body at right angles to the 

 latter, and, like them, consisting of spindle-cells. In the muscu- 

 lar integument, when split up lengthways, and properly stretched, 

 ilic longitudinal muscle-bands may easily be isolated in their 

 whole length, or in portions only, by passing a probe under one 



