182 PHYSICAL CHEMISTRY 



the PH of normal human blood, dropped through the air into 

 a relatively large volume of C0 2 -free salt solution, to vary from 

 7.49 to 7.64, but these high (alkaline) values are probably due 

 to faulty technique. Winterstein (1911) showed that if new 

 born pups are perfused with C0 2 -free saline, the respiratory 

 movements are not induced, but if a trace of HO is added to 

 the perfusing fluid, the respiration commences. It was shown 

 by Hasselbalch and Lundsgaard (1912) that the respiratory cen- 

 ter in anesthetized dogs is controlled by the H ion concentration 

 of the blood. Miilroy (1914) obtained similar results on dogs 

 and cats but claimed that the threshold of stimulation of the 

 respiratory center by H ions is lowered by lack of oxygen. This 

 apparent result of his experiments may be explained away in the 

 following manner : We may suppose that the respiratory center 

 is affected not by the reaction of the blood directly, but by its 

 own reaction, which is in a dynamic equilibrium with that of the 

 blood (by diffusion). During lack of oxygen acid substances 

 produced in the respiratory center fail to be removed by oxida- 

 tion, and hence the H ion concentration increases although that 

 of the blood remains constant. 



In the same way the lowering of the buffer value of the blood 

 in acidosis may affect the respiratory center. The lack of bi- 

 carbonate in the blood coming to the respiratory center decreases 

 its power of neutralizing the C0 2 produced by the center, and 

 increased breathing may result. This may cause a decrease in 

 the H ion concentration of the blood and decreased breathing. 

 In this way irregular or labored breathing may arise, the total 

 lung ventilation being increased owing to the low C0 2 tension 

 of the blood and alveolar air. That is to say, a given volume 

 of expired air would carry a subnormal amount of C0 2 , and, 

 hence, the lung ventilation must be increased in order to remove 

 the C0 2 from the body at the normal rate. The decreased buffer 

 value of the blood with lowered CO„ tension is shown in fig. 18. 

 Szili (1906) slowly injected HC1 into the blood of dogs until it 

 caused death. The PH of the blood of the dog at death was 

 about 7.05. 



Owing to the prompt regulatory action of the respiratory cen- 

 ter, the addition of acid within certain limits to the blood lowers 

 its buffer value or bicarbonate content, and hence lowers the C0 2 



