THE SIGNIFICANCE OF THE PULSE-RATE 

 IN VERTEBRATE ANIMALS^ 



By FLORENCE BUCHANAN, D.Sc. (Lond.), 



Fellow of University College, London 



[From the University Museum, Oxford] 



We should expect the frequency with which a heart beats to 

 be determined by its own properties — by its size, the minute 

 structure of its muscle fibres, the inorganic salts in and outside 

 the fibres, temperature, its relation to the nervous system, 

 etc. ; it probably is immediately determined by such things as 

 these. At present, however, we do not know the properties 

 in which the hearts of allied animals, beating with very different 

 frequencies, differ from one another and we are not therefore 

 in a position to point to the immediate determining factors. 

 All we know is that the properties, whatever they are, which 

 determine frequency have come to be such as to enable the 

 heart to serve the purposes of the animal to which it belongs. 

 It is proposed in this paper to attempt to ascertain whether 

 we can find out some of the diff'erent ways in which the 

 heart serves these purposes and whether, or to what extent, 

 alteration in frequency of beat is one. To do this we must 

 first know something about the different purposes for which 

 the heart is required in different animals. 



In the first place the amount of driving work the heart has 

 to do varies a good deal in the different craniate vertebrates 

 and both with the structure and the habits of the animal. In 

 fish, e.g.y it has only to pump the blood as far as the gills and 

 it has not much to do even in effecting this, as the passive 

 dilatation of the gill capillaries with each inspiratory movement 

 of the buccal cavity helps the blood to get there (i),^ In 

 accordance with this small amount of work we find the heart 

 to be of relatively small size in fish. Its weight in the common 

 round fish is on the average only 0*09 per cent, of the body 

 weight ; in the notably inert flat-fish it is even less, only 



' From a lecture delivered to the Oxford University Junior Scientific Club in 

 November 1909. 



^ These numbers refer to a list of authorities given at the end of the paper. 



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