146 



J. Lindhard. 



total volume respired following on the low carbonic acid tension 

 can be explained in one of two ways. Either substances are formed 

 in the blood under the influence of the light, which reduce the 

 threshold value of the carbonic acid tension, or the excitability of 

 the centre is increased by reflex action. The question as to which 

 of these two alternatives is correct, can scarcely be settled on the 

 basis of the material available at present. There is no doubt that 

 the light has some influence on the functions of the central nervous 

 system; various observations speak definitely in favour of this. On 

 the other hand, a considerable reduction in the alkalinity of the 

 blood was found on Monte Rosa. Whether this is due to the light, 

 I do not know; there are most probably no investigations on this 

 point. And the question of the alkalinity of the blood seems on 

 the whole to be at a very uncertain stage. 



Frequency of the respiration. 



If we study a text-book such as Vierordt's^, we get the im- 

 pression that the respiration-frequency was one of the best investi- 

 gated and most accurately determined, physiological functions. We 

 find it stated for example: 



A rise in the air-temperature of 1° C. reduces the frequency by 

 0054 per min. 



A rise in the barometric pressure of 1^/4 cm. increases the fre- 

 quency by 0*74 per min. etc. 



By far the most of these statements are taken from a work of 

 K. ViERORDT from 1845; this has not been accessible to me; but in 

 a later work of the same author ^ the experiments in question are 

 briefly discussed. 



ViERORDT gives the normal respiration-frequency to be 12 per 

 minute, but adds that it may rise under certain circumstances. With 

 increasing cold the frequency rises and at the same time the respi- 

 ration increases in depth; the frequency rises and falls with the- 

 air-pressure. 



These results are in direct opposition to what appears from my 

 material on almost every point; but the methods pursued by Vie- 

 RORDT are so full of shortcomings, that we hardly require to seek 

 for other causes for the disagreement. Vierordt inspires through 

 the nose and expires through a mouth-piece; this is not a natural 

 mode of respiration. Again he expires into a glass-receiver full of 

 salt solution, and must therefore expire against a greater or less 



1 Hermann Vierobdt: Anatom. Physiol, u. Physikal. Daten u. Tabellen. Jena 1906. 

 '^ Karl Vierordt: Grundriss d. Physiologie d. Menschen. Tübingen 1862. 



