532 EESPIRATION 



be varied at any time by conditions arising elsewhere in the body. 

 Moreover, these conditions may affect its activity in two ways, namely, 

 by means of the gaseous constituents of the blood as it passes by its 

 cellular components and secondly, by impulses conducted to it from 

 other parts of the body. 



The chemical regulation of respiration has a nutritive basis, because 

 it is a well-known fact that an increased venosity of the blood supplying 

 the center immediately leads to an augmentation of the respiratory 

 movements. Conversely, a greater aeration of the blood gives rise to a 

 lessened respiratory frequency and amplitude. It is readily possible 

 to change a dyspneic type of breathing into an apneic type, and 

 vice versa. In either case, the question immediately arises, whether 

 the oxygen or the carbon dioxid is the stimulating agent. Thus, it 

 may readily be surmised that the respiratory movements may be 

 rendered dyspneic either by decreasing the amount of the oxygen 

 (Rosenthal), or by increasing the quantity of the carbon dioxid 

 (Traube) . The evidence, recently collected by Haldane and his pupils, ^ 

 seems to show that neither one of these factors can be ruled out abso- 

 lutely. It is very obvious, however, that the center is especially sen- 

 sitive to changes in the carbon dioxid content of the blood ;2 in fact, 

 thS stimulating potency of this gas is so great that, under normal con- 

 ditions, the oxygen cannot play an important part in the regulation 

 of respiration. It is true, however, that these two conditions gener- 

 ally go hand in hand, because an increased production of carbon dioxid 

 necessitates a greater intake of oxygen. 



In illustration of this statement, it might be mentioned that a 

 decided augmentation of the respiratory movements can only be 

 attained if the oxygen pressure of the alveolar air is reduced from its 

 normal value of 20 per cent, to about 13 per cent, of an atmosphere. 

 In fact, in many instances the subject of the experiment is absolutely 

 unaware of any scarcity of oxygen, although the color of his skin and 

 mucous surfaces clearly betrays a marked deficiency in oxyhemoglobin. 

 Unconsciousness frequently sets in before an augmentation in the 

 respiratory rate has been noticed. Consequently, the action of the 

 oxygen upon the center seems to consist merely in its preventing the 

 accumulation of the products of metabolism by quickly oxidizing them. 

 Whenever this gas is present in insufficient amounts, the cells soon 

 become overloaded with these waste products. This condition in- 

 creases their irritability so that the carbon dioxid finally acquires a 

 greater potency as a respiratory stimulant.^ 



Much more decisive results are obtained with carbon dioxid, 

 because an increase in the tension of this gas in the alveolar air of only 

 2 per cent, suffices to increase the pulmonary ventilation 50 per cent. 

 A rise of 3 per cent, increases it 126 per cent, and a rise of 6 per cent. 



1 Jour, of Physiol., xviii, 1895, 442, and xxxii, 1905, 225. 



2 Zuntz, Pfluger's Archiv, xcv, 1903, 192. 



3 Haldane and Poulton, Jour, of Physiol., xxxvii, 1908, 390. 



