166 SECTIONAL ADDRESSES. 



a pulse rate of 70, a systolic arterial pressure of 120 mm. Hg, a red cell 

 count of 5,000,000 per cubic mm. or an alveolar carbon dioxide pressure 

 of 40 mm. Hg, &c., and we can investigate the means by which this 

 constancy is reached. But for other purposes it is equally convenient to 

 regard each of these in turn as variable, to study its variations and find 

 how they are produced. When we do so we find with increasing clearness 

 the more deeply the subject is investigated, that the variability and the 

 constancy are closely related, the fi^ed value of one thing being due to 

 the interplay of the variables of others. Thus the constancy of the alveolar 

 00,2 pressure may be regarded as due to the interaction of such variables 

 as hydrogen ion concentration of blood, body temperature, ventUation 

 rate, oxygen pressure, &c., by which a state of equilibrium is maintained. 



We have in the study of physiology many beautiful examples of this 

 closely woven texture of interdependent phenomena. Modify any condi- 

 tion concerning any one of them, and you at once set the machinery moving 

 in such a way as to counteract what you have done. And this is not what 

 life is but what it does, which distinguishes it — it adjusts the organism to 

 its environment. 



There is a striking though superficial resemblance between this principle 

 of biological adaptation and the principle of Le Chatelier of ' the opposi- 

 tion of a reaction to further change ' which is expressed ' when any system 

 is in a state of physical or chemical eqmlibrium, a change in one of the 

 factors of equilibrium will cause a reverse change within the system.' 



In living things, however, as Donnan has remarked, ' the activities, 

 and indeed the very existence, of a living organism depend on its con- 

 tinuous utilisation of an environment that is not in thermodynamic 

 equilibrium. A living organism is a consumer and transformer of external 

 free energy, and environmental equilibrium means non-activity and 

 eventual death.' Nevertheless, as Claude Bernard believed, and as 

 Henderson has strikingly illustrated, the internal environment is main- 

 tained very constant in certain respects, and this constancy is the outcome 

 of special activities which characterise life. 



Glancing now towards the future, what may we say represents in a 

 few words the trend of modern physiology ? In many ways a great future 

 lies before it. Utilising the other sciences as its tools and itself reacting 

 powerfully on them, we can confidently predict progress to undreamt-of 

 heights, an enormous development of experimental pathology and medicine, 

 and far-reaching eSects on economic and sociological conditions. Yet, 

 implicit in these very potentialities, there is another and a gloomier side 

 to the picture. The rapidly accumulating wealth of detailed knowledge 

 and of special technique demands an increased specialisation ; unless 

 there is a periodic intellectual stocktaking there must inevitably be a loss 

 of perspective and of grasp of great general principles. But how can 

 this stocktaking be done ? Can team work ever reach that harmony of 

 action which distinguishes the individual ? Any scientific subject is 

 capable of indefinite expansion, and with the biological sciences it is hard 

 to foresee what the ultimate end of mere expansion can be. How will 

 scientific literature develop ? Will there have to be abstracts of abstract 

 journals and reviews of reviews ? Will the subdivision of the subject 

 necessitate in the long run the creation of lectureships or professorships 



