MOUNTAIN SICKNESS. 93 



tion, while, on the other hand, heart-failure, owing to the 

 imperfect circulation, and therefore imperfect aeration of 

 the blood, is a common and well-recognised cause of 

 dyspnoea or asphyxia. If dyspnoea or asphyxia leads 

 at altitudes of between 16,000 and 17,000 feet to heart- 

 failure on moderate exertion, a vicious circle is produced, 

 since the asphyxia tends to produce heart-failure, and vice 

 versa. 



If this be the case, the limits of mountain climbing, as 

 regards height which can be reached, become more re- 

 stricted than would be the case if we had to deal with 

 asphyxia alone. 



To state the point' about heart-failure more clearly, let 

 me insist that the heart is a pump, which must pass on in 

 healthy man or animals an amount of blood, which varies 

 greatly at different times, in order to meet the requirements 

 of the system as a whole. If the heart's work (expressed 

 by the quantity of blood passed on, and the hydrostatic 

 pressure against which this blood is expelled) be increased 

 beyond a given limit, the heart as a pump becomes in- 

 efficient from dilatation of the ventricles, so that the valves 

 between the latter and the auricles, can no longer close 

 completely. This inefficiency of the cardiac pump can be 

 produced in two chief ways. Firstly, by increasing the 

 work thrown upon the heart ; and, secondly, by diminishing 

 the power of the heart. The diminution in power of heart 

 can be produced by a great many causes, one of which is 

 imperfect supply of oxygen to the organ. Others are, 

 alcohol, tobacco, tea, disease of the heart, etc. Increase of 

 work may be given by muscular exertion, fever, mental 

 excitement, etc., etc. Any one of all the above causes is 

 capable by itself of producing heart-failure. In most cases 

 two or more of them are combined. For example, there can 

 be little doubt, from the observations of Clifford Allbutt 

 and others, that many of the cases of the mountain sickness 

 which occurs at low altitudes, and which has so often been 

 described in the Alps and elsewhere, are really cases of 

 heart-failure from over exertion and imperfect training, 

 combined perhaps in some cases with error in diet. 



