162 ELECTRO-PHYSIOLOGY CHAP. 



tion is conveyed by nerves, or where it transmits itself from cell 

 to cell by direct propagation. Both alternatives seem actually to 

 be present. 



In the heart, Engelmann (22) was the first to investigate 

 these relations, A. Fick (23) having previously made a short 

 communication on the subject. If a resting frog's ventricle, 

 separated from the auricle, is stimulated at any given point, 

 a general contraction (systole) of the hollow muscle follows, so 

 that the excitation must have been distributed uniformly in 

 all directions from the point of stimulation by conductivity. 

 Engelmann showed that the ventricle need not necessarily be 

 uninjured ; the experiment succeeds well if the ventricle of a 

 freshly-killed frog is divided by scissors into two or more pieces, 

 connected only by a minute bridge of muscle-substance ; after a 

 time all the pieces will contract successively when any one of 

 them is stimulated. It is quite indifferent at what point each 

 bit is joined to the others, the only essential is that they should 

 l)e united by muscular substance. The experiment in this form, 

 therefore, indicates " that excitation can be transmitted in the ven- 

 tricle from any point, to any other point, by any given point." 

 The complete conductivity of the separate muscle bridges, which 

 is disturbed at first, comes back gradually after a certain time has 

 elapsed perhaps an hour or longer. If a bit of the ventricle is 

 left in connection with the beating auricle, this bit, when con- 

 ductivity has been fully re-established, will contract first after 

 each auricular systole, then the next, and so on. The contraction 

 is propagated, therefore, in a peristaltic direction from base to 

 apex of the ventricle. If the preparation is no longer beating 

 spontaneously, the succession in which the individual pieces 

 contract will depend only on which piece was first excited, since 

 the contraction proceeds from this successively to all the others ; 

 no part is ever omitted. Since we are a priori forbidden on 

 histological grounds, as well as from the low velocity of excita- 

 tion, to assume that each cell is united with its neighbours by 

 nerve-fibres, the second view only is admissible, i.e. that excitation 

 (contraction) proceeds directly from cell to cell in the saim- 

 manner as within each single cell. 



The time-relations of the process of contraction have already 

 been described, in so far as concerns the " twitch " of cardiac 

 muscle. It only remains to consider the rate of conductivity, 



