164 ELECTRO-PHYSIOLOGY CHAP. 



rapidity of transmission in motor frog's nerves under the same 

 conditions. Hence it would appear as if muscular conduction 

 from auricle to ventricle could be as certainly established as 

 within the auricle and ventricle. However much the magnitude 

 of the velocity of muscular excitation may depend on different 

 states of the muscle (fatigue, temperature), it can be maintained 

 under some conditions notwithstanding considerable alterations 

 in the muscle-substance. Thus it would appear that with partial 

 turgescence of the frog's sartorius, the tracts affected may com- 

 pletely lose the power of contracting, without to any extent 

 suffering in regard to electrical sensibility, or conductivity 

 (Biedermann, 24). The same applies, according to Engelmami 

 (7.c.), to the muscle bridges of the auricle in the frog's heart, 

 which, " after complete abolition of their contractility, are still 

 able to transmit the motor stimulus to the ventricle, and that 

 with the same rapidity as if the power of contracting was 

 uninjured." 1 



It cannot be doubted that the same relations of conductivity 

 of excitation described above for the frog's heart, obtain in the 

 cardiac muscle of higher vertebrates, and this is of the more 

 consequence since there is in general, e.g. in mammals, a much 

 less extensive contact of the separate, short, and broad muscle-cells, 

 which really unite only by their blunt end-surfaces and short 

 lateral branches. Similar relations exist, again, in the intestine of 

 insects and myriapods, the walls of which contain anastomosing, 

 striated (uninuclear) muscle - cells, which by contraction set up 

 the normal, peristaltic movements of the digestive tract. Engel- 

 mann (25) considers the intestine of the fly to be the most 

 suitable object for combined anatomical and physiological investi- 

 gation, more particularly the opening of the end of the intestine, 

 from the mouth of the Malpighian tubules to the rectum. " The 

 muscular integument here consists essentially of a single layer of 

 strong, striated circular fibres, enclosed within an unmistakable sar- 

 colemma (invariably absent in cardiac muscle-cells), and separated 

 by perceptible spaces from another." Each fibre seems to be 

 joined to its neighbours by one, or several, oblique or sometimes 



1 Kaiser (Zeitschr. f. Biologic, 1894) has recently criticised the cogency of the 

 evidence in these experiments, and refers the effects observed to current diffusion. 

 This can only be ascertained by further experiment, for which we have not yet had 

 opportunity. 



