158 SECTIONAL ADDRESSES. 



integrity is no longer preserved. The history of the development within 

 recent years of our ideas about respiration has afforded a striking example 

 of the application of such methods. Twenty-two years have elapsed 

 since the publication of Haldane's and Priestley's classical paper on the 

 regulation of the lung ventilation. Up to that time our knowledge about 

 the breathing was surprisingly small : we accepted the fact of the apparent 

 aixtomaticity of the breathing, and recognised that the respiration adjusted 

 itself suitably to changes in bodily activity, but we had no satisfactory 

 explanation to offer ; isolated facts were known, but we could not combine 

 them into an intelligible whole. Then suddenly light was thrown on the 

 whole situation by a series of experimental observations on human subjects 

 in full possession of their normal faculties and with their natural powers of 

 response to changes in their immediate environment unimpaired. The 

 reason for the activity of the respiratory centre in the brain was shown 

 to be due in the main to the fact that it was sensitive to the actual concen- 

 tration of CO., in the arterial blood which reached it. A trifling rise in 

 this concentration above the value shown during quiet breathing at once 

 caused hyperpnoea, a trifling fall was at once followed by reduction, if 

 not complete cessation of the breathing. As the determining factor was 

 apparently the concentration of CO, 2 in the arterial blood, a concentration 

 set by the composition of the air in the depths of the lungs, it became 

 evident that the activity of the respiratory centre was proportional to 

 the mass of CO., produced in the body and carried to the lungs, and this 

 in turn implied that the quantitative correlation of the ventilation of the 

 lungs with the changes of metabolism in the body as a whole was ensured 

 by chemical means. From this work, too, we gained our first real insight 

 into the amazing delicacy of true chemical correlation within the organism. 



Since that date innumerable contributions have been made to the 

 physiology of the breathing, and the bulk of these have been made with 

 man as the subject of investigation. We recognize now that the respiratory 

 centre is sensitive not to C0. 2 as such but to changes in the hydrogen ion 

 concentration of the blood, that lactic acid accumulation as well as increased 

 C0 2 production must be taken into account when studying the hyperpnoea 

 caused by muscular exertion, and that reduction in the oxygen concentra- 

 tion in the arterial blood and alteration in the temperature of the blood 

 may play contributory parts. Yet in spite of this, the fundamental con- 

 ception of accurate chemical or physico-chemical co-ordination of function 

 remains unimpaired : so long as the respiratory centre is sensitive to 

 chemical or physical changes which result from alterations in activity of 

 the different organs, the quantity of air breathed must be co-ordinated 

 with the varying metabolism of the body. 



And when once we have ascertained the quantitative alterations in the 

 respiratory exchange which correspond with our varying activity during 

 the course of the day, and have grasped the fact that the breathing is 

 automatically adjusted in correspondence with the tissue metabolism, 

 because the cells of the tissues are so intimately linked with the respiratory 

 centre in the brain by the blood stream that the degree of activity of the 

 respiratory centre is actually determined by the events in those organs 

 whose metabolism happens to vary, we are led on logically to a further 

 inquiry. For so delicate an adjustment of the breathing in conformity 



