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PRINCIPLES OF GENERAL PHYSIOLOGY 



(probably as a secondary effect) to diminish the relative amount of reserve material 

 consumed. The sugar does not appear to be completely oxidised, since, especially 

 under the action of cyanide, organic acids and aldehydes are formed. The effect 

 of increase of carbon dioxide is interesting. Here there is no evidence of abnormal 

 forms of oxidation of glucose, and yet the amount of pressure produced per unit 

 of oxygen consumed is enormously depressed. The pressure produced, in fact, 

 falls almost to zero, yet the oxygen consumed continues to be more than half that 

 of the normal period. It seems that the chemical processes go on normally, but 

 the change of chemical to mechanical energy is prevented by carbon dioxide. 



The experiments of Mines (1913, 3) have shown the importance of H - ion con- 

 centration as regards the spon- 

 taneous beat of the heart. He 

 finds that there is an optimal con- 

 centration. Excess may abolish the 

 mechanical change while the elec- 

 trical change may remain intact. 

 The absence of Ca" ions has the 

 same effect, as shown in Fig. 172 

 (page 539). 



THE ORIGIN OF THE HEART BEAT 



Whatever may be the impulses 

 that cause the heart to beat 

 rhythmically in certain inverte- 

 brates, as in Limulus, where Carlson 

 (1904) showed that they are given 

 off by ganglion cells, there is no 

 doubt that the heart muscle of the 

 vertebrate is capable of rhythmic 

 beats in the absence of nerves. 

 This fact is shown most conclusively, 

 perhaps, by the experiments of 

 Burrows (1912), who showed that 

 bits of heart muscle from embryo 

 chicks continued to beat in blood 

 plasma as long as thirty days, and 

 that cells wandered off from the 

 mass and continued to multiply. 

 The newly formed cells then com- 

 menced to beat rhythmically. 

 Similar facts are described by 

 Margaret R. Lewis (1915) for 

 skeletal muscle. 



It was first definitely shown by 

 Gaskell (1882) that all the pheno- 

 mena observed in the hearts of the frog and tortoise are to be explained satis- 

 factorily on the basis of a " rnyogenic " origin, that is, not only does the beat arise 

 spontaneously in muscular cells, but also the conduction of the excitation from 

 one part of the same heart cavity to another part of that cavity, and from 

 one cavity to another, takes place by muscular tissues. A portrait of Gaskell 

 will be found in Fig. 229. This view was taken up by Engelmann on the 

 Continent, and powerfully supported by his work. Now, while there is no 

 difficulty, as far as muscular continuity is concerned, in the case of the lower 

 vertebrates, it was believed, -until the work of Stanley Kent (1893) and of His 

 (1893), that there is no muscular continuity between the auricles and ventricles 

 of the mammal. These observers showed that there is a bundle of a special 

 kind of muscle fibres at a particular place, putting the muscular structures of 

 auricle and ventricle into direct connection. The anatomy of the "bundle of 



Usui^ 



FIG. 229. PORTRAIT OF (JASKELL. 



(From a negative l>y V. H. Mottram.) 



