RELATION OF PHYSIOLOGY TO MEDICINE. 91 



of them. This, for instance, is what Huxley expressly 

 aimed at in his admirably written Elementary Physiology. 



Now I entirely agree with this contention ; but the 

 question remains as to what are the facts. It seems to 

 me that, quite unconsciously, Huxley, and the whole 

 physiological school which he typifies, misrepresented 

 them very seriously, and in the manner which is really 

 responsible for the existing and very detrimental 

 estrangement between practical medicine and the pre- 

 liminary medical sciences. It is quite evident that the 

 breathing is regulated in the manner just described. 

 One can verify it with the greatest ease. But if we 

 teach physiology as if it dealt with a series of essentially 

 unconnected events, like the workings of the separate 

 parts of a machine, we misrepresent the facts. 



We know, for instance, that under ordinary conditions 

 the presence of a certain very minute excess or deficiency 

 in the pressure of carbon dioxide in the alveolar air will 

 cause great increase in the breathing, or bring natural 

 breathing to a complete standstill. This seems simple 

 and definite ; but as soon as we alter the conditions 

 by diminishing the normal pressure of oxygen in the 

 air, or interfering with the circulation, or overdriving 

 the muscles, or making the diet abnormal in certain 

 directions, or in various other ways altering the " normal " 

 conditions, the statement is no longer true. The definite 

 effect of the CO 2 is no longer the same. The effect 

 depends very directly on the normal functioning of the 

 body as a whole, and its immediate environment ; and 

 when we consider the alteration in the effect we find that 

 it is again regulative in the sense of contributing to 

 maintenance of the normal, though in a wider sense 



