THE REGULATION OF RESPIRATION 559 



gas during internal respiration, for the increasing carbon dioxide 

 in the capillary blood-vessels would raise the partial pressure of 

 oxygen and maintain it, when the quantity of the gas was 

 diminishing. The production of lactic acid during muscular work, 

 when the supply of oxygen is insufficient, would act indirectly in 

 a similar manner, for it would increase the pressure of carbon 

 dioxide. The breathing of carbon dioxide may thus be useful 

 in cases where the supply of oxygen to the tissues is insufficient, 

 for the pressure of oxygen would be raised, and thus more would 

 be rendered available for absorption by the tissues. The con- 

 centration of the blood during its passage through active organs 

 would also raise the pressure of the oxygen in the blood of the 

 capillaries, and Bohr maintains that the alteration in the " specific 

 oxygen capacity " of the blood during its flow through the 

 capillaries will also act in a similar favourable manner. 



The part which is played by such factors and by the intra- 

 cellular ferments in the processes of internal respiration must be 

 determined by future research. The little that is known at present 

 is exceedingly interesting and suggestive in connection with many 

 physiological and pathological problems. Internal respiration is 

 probably a far more complex process than it appeared to be only 

 a few years ago. 



The Regulation of Respiration in Health and Disease. It might 

 appear that the oxidation of the body is determined by the amount 

 of combustible material and the supply of oxygen, for the activity 

 and vascularity of an organ are so closely associated that under 

 ordinary conditions they are inseparable. The numerous experi- 

 ments upon internal respiration show, however, that the condition 

 of the cells, not the supply of oxygen, determines the process of 

 respiration both as regards the absorption of oxygen and the dis- 

 charge of carbon dioxide ; the animal is able to vary the supply 

 of oxygen and the removal of carbon dioxide according to its 

 needs. 



In the preceding chapters ample evidence has been given of 

 the variations in the respiratory exchange of the whole body and 

 of its several parts under different physiological conditions, but 

 so far the regulation of the ventilation of the lungs according to 

 the needs of the organism has not been considered. This is a 

 subject of the greatest practical importance to the physician, for 

 he is forced by the exigencies of his practice to gauge the respira- 



