310 Appendix I. On methods 



Within the last few years a good deal of energy has been expended by the 

 protagonists of each theory; the general motif of which has been to shake confidence 

 in the results obtained by the opposing theory. 



In so far as I have had an opportunity of seeing the two methods at work on the 

 same individual (and I believe that this test has rarely been performed) the two 

 methods gave an identical result, that being so it seemed to me rather a work of 

 supererogation for the supporters of one method to be so suspicious as to the 

 validity of the other. 



This however was at or near the sea-level, and it is at great altitudes that the two 

 methods are described as giving most divergent results, the method of Zuntz giving 

 lower readings for the oxygen alveolar air than the method of Haldane and Priestley 

 We may therefore make some criticisms upon the two methods. 



(1) There is underlying the method of Zuntz and Loewy, or at all events under- 

 lying their application of it, the assumption that the dead space is a constant quantity. 

 This, as Haldane has pointed out, is probably very far from being the case. The 

 respiratory passages, at all events the smaller ones, all have a rich musculature in 

 their walls. They are, in fact, like arteries which admit air instead of blood. The 

 physiology of the bronchial muscles leaves much to be desired. It has mostly been 

 studied from the point of view of asthma, and therefore it is the contraction of the 

 muscles as compared with the normal tone which has claimed attention. It is, how- 

 ever, not improbable that our notions about the bronchial muscles are as distorted as 

 those of the arteries would be if we merely considered the changes from the normal 

 arterial tone of the resting organ to that of pathological arterial spasm. In the case 

 of the artery the functional significance of the musculature of the arterial wall is that 

 it can relax to let the organ have the amount of blood which it requires when it is in 

 full activity. There is no reason to doubt that the functional significance of the 

 bronchial muscles is to relax during conditions of exalted respiration and allow 

 perhaps ten times the ordinary quantity of air to pass through the tubes without let 

 or hindrance. When we recollect that the volume of a cylinder increases with the 

 square of its diameter it will be easily seen that the dead space of the lung may 

 increase without difficulty two or three-fold under conditions such as those obtaining 

 at high altitudes, in which the respiration is quicker than usual. Of the mechanism 

 of such dilatation we are in ignorance, it may be medullary ; it may be the effect of 

 changes in the blood*. 



The neglect of this factor may be one reason why Zuntz's method diverges from 

 that of Haldane's at high altitudes. This neglect would tend to make Zuntz and 

 Loewy's results for the oxygen pressure in alveolar air too low. 



If however one concedes that the dead space of the lung may be two or three times 

 as great during conditions of deep or rapid respiration, as under ordinary circumstances 

 one must ask oneself whether by a violent deep expiration such as is made for the 

 purpose of Haldane's alveolar air determinations, it is possible to clear the air space 

 as efficiently as one does under normal circumstances. 



It would be most desirable that someone should make himself thoroughly con- 

 versant with both methods and make a more systematic comparison of the two than 

 has yet been done. 



* Since this was written the work of Krogh has appeared (Journal of Pliysiol. Oct. 1913). 



