2 2 4 THE CONTRA CTION OF CARD I A C MUSCLE. 



in a .special manner on the sinus. In accordance with this, he 

 finds, and Pickering l confirms his observations, that muscarine is in- 

 effective on the hearts of embryos when they first begin to beat. In 

 other words, muscarine is asserted to be ineffective unless certain nerve 

 cells, which are supposed to constitute an inhibitory centre, are present. 

 Curiously enough, Pickering finds that under the same circumstances 

 pilocarpine, which in other respects acts like muscarine, is effective at a 

 time when muscarine is unable to produce standstill. It seems to me 

 that we are dealing here only with a question of degree, and not with a 

 question of fundamental difference of action. Some tissues are more 

 resistant than others, and their resistance in the embryo differs from 

 that in the adult. 



Finally, Eansom's 2 experiments upon the heart of Cephalopods give 

 very conclusive evidence upon this question, for he has shown, in the 

 first place, that atropine does not paralyse the inhibitory nerve, though 

 curari does ; in the second place, that muscarine will produce standstill 

 in this heart as in others, and yet that atropine will antagonise the 

 action of muscarine. Clearly in this case the antagonistic action of 

 atropine to muscarine cannot be explained by the supposition that mus- 

 carine stimulates inhibitory fibres. 



Vulpian also asserts that muscarine will produce standstill in the 

 snail's heart, and atropine removes that standstill. 



We may, it seems to me, sum up the action of these poisons on the 

 vertebrate heart in physiological amounts thus : — 



Nicotine and curari break the connection of the pre-ganglionic fibre 

 with the nerve cell. 



Atropine acts on the muscular tissue to a slight extent tonically, 

 breaks the connection between the post-ganglionic fibre and the muscle, 

 and also the connection between the pre-ganglionic fibre and the nerve cell. 



Muscarine, etc., act on the muscular tissue atonically. 



Digitaline, etc., act on the muscular tissue tonically. 



The Nutrition of the Heart. 



The beating of the isolated ventricle or apex is dependent, not only on 

 the pressure of the fluid in its cavity, but also upon the nature of that 

 fluid, and a large number of observations have been made for the purpose 

 of finding out what are the constituents which a fluid must contain in 

 order to maintain good contractions of the cardiac muscle. The earlier 

 experiments largely emanated from Ludwig's laboratory, under the 

 guidance especially of Kronecker, and were started by Bowditch's 3 

 discovery that delphine was able to make the isolated apex of the heart 

 beat more or less rhythmically. This paper was followed in 1872 by 

 that of Luciani, 4 who showed not only that the frog's ventricle was able 

 to beat when supplied with serum, but also that its contractions were not 

 always regular like those of the intact heart, lint during a portion of the 

 time of action of the serum occurred in distinct groups, with pauses of 

 varying lengths between the groups. Two distinct questions thereupon 

 arose — (1) What are the constituents of serum which enable the ventricle 

 to continue beating ? and (2) what is the meaning of this periodicity ? 



1 Journ. PliysioL, Cambridge and London, vol. xiv. p. 449. 



- Op. c//. 3 Op. ril. 



4 Ber. d. /,•. Sachs. Gesellsch. <L Wissetisch.-. Leipzig, 1873, N. 11. 



