442 Physiology and Pathology of Mammalian Heart. [Feb. 11, 



nerves upon the individual contractions less in the former case, but 

 also that the fatigued and therefore dilated heart is per se unfavour- 

 ably placed for meeting increase in the work thrown upon it. An 

 explanation is given of the reason why in heart disease failure takes 

 place during exertion. 



The part played by the vagus in protecting the diseased heart from 

 harmful over- work is referred to, and it is shown that irregularity of 

 the heart in disease may be explained by the mode in which this 

 nerve, when acting powerfully, releases the ventricles from the con- 

 trol of the rhythmic centre in the sinus. The chief forms of rhythmic 

 and arrhythmic irregularity are considered, and it is shown that these 

 correspond with the forms of irregularity which can be produced by 

 vagus action. The irregular heart expends more energy, and its 

 tissues therefore are more wasted, for a given amount of work than 

 the heart which is beating regularly. 



The effect upon the heart of imperfect aeration of the blood is, first 

 of all, to produce powerful vagus action from the medullary centre; 

 this is usually, though not always, accompanied in curarised animals 

 by diminution of the output of the heart. But reasons are given for 

 assuming that the output would be increased in uncurarised animals, 

 owing to the high venous pressure which results from struggling. 

 Besides the vagus action, it can be shown that asphyxia causes pro- 

 gressive weakening both of the auricles and of the ventricles, and 

 attention is drawn to the fact that the considerable rise of pressure 

 in the systemic arteries in asphyxia is accompanied by vagus effects 

 upon the heart, and not by augmentor action, as is the case, so far 

 as we know, in all other instances in which the vaso- constrictor 

 centre is excited in the normal individual. 



It is noted that the change in the heart and circulation which takes 

 place during asphyxia points to the conclusion that, when the total 

 amount of oxygen in the blood is lowered, it is for the benefit of the 

 economy that those organs, such as the central nervous system, whose 

 continuous blood supply is a vital necessity, should be richly furnished 

 with blood by constriction of the vessels of the spleen, kidney, and 

 digestive system, whose blood supply can be cut off temporarily with- 

 out danger to life, and also that the heart should carry on the circu- 

 lation in a manner involving as little as possible waste of its own 

 substance. This, as we have seen, it is the function of the vagus 

 nerve to bring about. 



III. " The Role played by Sugar in the Animal Economy. 

 Preliminary Note on tbe Behaviour of Sugar in Blood." 

 By VAUGHAN BARLEY, M.D. Communicated by GEORGE 

 HARLEY, M.D., F.R.S. Received January 4, 18 C J2. 



