[Peoc. Rot. Soc. Victoria 29 (N.S.), Part I[., 1916]. 

 Aiir. VIII. — Oscillatory Adjustments in the Animal Body. 



By W. A. OSBORNE, M.B., D.Sc. 

 (Professor of Physiology in Melbourne University), 



[Eead 22nd September, 1916.] 



Ostwald has pointed out that if any system be self-adjusting the 

 equilibrium attained must necessarily be oscillatory. As an illustra- 

 tion of this, he cites the thermostat, where the regulator shuts off 

 the heat supply when a certain standard temperature has been ex- 

 ceeded. The result of this withdrawal is a fall of temperature below 

 the desired level; to be succeeded by a rise and so forth. The better 

 the regulating mechanism the smaller are the oscillations, and the 

 best device is that in which the amplitude of the variation is re- 

 duced to a negligible quantity. As Ostwald points out, this 

 principle can be extended to human affairs; in politics, for instance, 

 there is always the tendency for opinion to oscillate between radical 

 and conservative positions; in the realm of the aesthetic standards 

 of taste move to and fro between the florid and the austere. I pur- 

 pose to apply this principle to some aspects of animal physiology, 

 for in the animal body we find numerous adjustments which are 

 relatively constant, and which maintain constancy by self-regulating 

 mechanisms. Amongst the many physiological landmarks in evolu- 

 tion the transformation of a variable into an invariable (tempera- 

 ture, osmotic pressure, etc.) has been conspicuous, but we are com- 

 pelled to assume that, however close to a fixed standard the adjust- 

 ment is made, if a self-regulating mechanism is at work a state of 

 oscillatory equilibrium has been established. A number of instances 

 may now be discussed. 



I. Respiration. — We owe to Haldane^ and his school the discovery 

 of the chemical regulation of pulmonary ventilation. If metabolism is 

 not too active as it is in violent exercise there is a remarkable con- 

 stancy shown in the COg tension of the alveolar air. This means a 

 similar constancy in the tension of COj in the arterial blood, and 

 the standard attained is just that which is adequate to excite the 

 respiratory centre in the medulla oblongata. It does not affect the 

 argument if we hold that CO 3 is the specific excitant, or whether it 

 is the hydrogen ion which is causative. Now, in health, the oscil- 

 lations above and below the mean of quiet respiration are so 

 damped that they escape recognition (though it is just possible that 



I The Regulation of the Lung Ventilation, J. Physiol., vol. 32, p. 225, 19C4. 



