162 SECTIONAL ADDRESSES. 



promoting the normal working of the body. We cannot restrict ourselves 

 here to a consideration only of the physico-chemical properties of the blood 

 and tissue fluids, for the initiation of any alteration in the hydrogen ion 

 concentration of the blood will at once result in a- change in the activity 

 of the respiratory, circulatory and excretory organs, the net effect of which 

 will be to render the actual change of hydrogen ion concentration a great 

 deal less than would otherwise be the case. Thus we see that the reactions 

 provoked in response to changed conditions will tend to preserve the 

 functional capacity of the body by limiting the changes in the immediate 

 environment of the tissue cells. 



The experimental investigation of man has furnished the clearest 

 evidence of co-ordination of organ activity of this type. The reaction 

 to muscular work is a case in point, for the increased activity of the respira- 

 tion and circulation, by hastening the elimination of C0 2 from the body, 

 helps to keep within reasonable limits the rise of hydrogen ion concentra- 

 tion in the blood caused by the passage of greatly increased amounts of 

 C0. 2 , and even lactic acid, from the active muscles into the blood stream, 

 and at the same time maintains the oxygen supply. The limitation of 

 the changes of hydrogen ion concentration in the blood, which is brought 

 about by simultaneous changes in the activity of the respiratory centre 

 and in the rate of excretion of acid and basic radicals by the kidney, has 

 been demonstrated in man when acid or alkali is temporarily withdrawn 

 from the body during the secretion of the digestive juices just as clearly 

 as when an excess of acid or alkali gains admission to the body owing 

 either to alteration of the diet or to the deliberate ingestion of alkalies, 

 such as sodium bicarbonate, or substances, such as ammonium chloride, 

 which lead to the liberation of acid within the body. There is evidence, 

 too, from experiments on man that in the tissues themselves a still narrower 

 limitation of changes of hydrogen ion concentration than in the arterial 

 blood may be attained by local acceleration or retardation of the circula- 

 tion. 



In the influence of training on a man's capacity for strenuous muscular 

 exertion, and in the process of acclimatization to the reduced oxygen 

 pressure in the atmosphere at high altitudes — a process to which changes 

 in the activity of the respiratory organs and kidneys and in the composition 

 of the blood all contribute — we get further examples of the co-ordinated 

 accommodation of organ activity to alteration in the conditions of life. 



The more we examine the normal behaviour of the body the more is 

 it brought home to us that the maintenance of the natural life and integrity 

 of the organism depends on the closest co-ordination of all its different 

 parts ; all the organs are interdependent, and can have no real existence 

 save as active components of a corporate whole. Life consists of a 

 delicate balance of all the different functions, a balance that is being con- 

 tinually adjusted so as to ensure the maintenance of the true functional 

 capacity of the organism in its struggle for self-preservation in a constantly 

 varying environment. As an agent in securing this exquisite co-ordina- 

 tion a physico-chemical change in the blood stream may at one moment 

 be prominent, at another moment a nervous reflex. Very frequently 

 both factors co-operate, the physico-chemical change ensuring perhaps 

 strict quantitative co-ordination of activity, the nervous reflex offering 



