90 



CONDITIONS INFLUENCING THE GASEOUS EXCHANGES. 



Regnault and Reiset found that a dog gave off 79 per cent, of the O inspired after 

 a flesh diet, and 91 per cent, after a diet of starch. If easily oxidisable substances 

 (glycerin or lactate of soda) are injected into the blood, the O taken in, and the 

 C0 2 given off, undergo a considerable increase (Ludwig and Scheremetjewsky). 

 Alcohols, tea, and ethereal oils diminish the C0 2 (Prout, Vierordt). [Ed. Smith 

 divided foods, with reference to the excretion of C0 2 , into two classes. The respira- 

 tory excitants include nitrogenous foods, rum, beer, sugar, stout, &c. ; the non- 

 exciters starch, fat, some alcoholic mixtures. The most powerful respiratory 

 excitants, however, are tea, sugar, coffee, and rum, and the maximum effect is 

 usually experienced within an hour. He also found that the effects produced by 

 alcoholic drinks varied with the nature of the spirituous liquor. Thus brandy, 

 whisky, and gin dimmish the amount ; while pure alcohol, rum, ale, and porter 

 tend to increase it.] 



8. The number and depth of the respirations have practically no influence on the 

 formation of C0 2 or the oxidation-processes within the body, these being regulated 

 by the tissues themselves, by some mechanism as yet unknown (Pjiiiger). They 

 have a marked effect, however, upon the removal of the already formed C0 2 from 

 the body. An increase in the number of respirations (their depth remaining the 

 same), as well as an increase of their depth (the number remaining the same), causes 

 an absolute increase in the amount of C0 2 given off, which, with reference to the 

 total amount of gases exchanged, is relatively diminished. The following example 

 from Vierordt illustrates this: 



9. Exposure to a bright light causes an increase in the C0 2 given off in frogs, 

 in mammals and birds, even in frogs deprived of their lungs, or in those whose 

 spinal cord has been divided high up. The consumption of O is increased at the 

 same time. The same results occur in blind persons, although to a less degree. 

 Bluish- violet light is almost as active as white light, while red light is less active. 



10. The experiments of Grehant, on dogs, seem to show that intense inflammation of the 

 bronchial mucous membrane influences the C0 2 given off. 



11. Amongst poisons, thebaia increases the C0 2 given off, while morphia, codeia, uarcein, 

 narcotin, papaverin, diminish it (Fihbini). 



128. DIFFUSION OF GASES WITHIN THE LUNGS. The air within the air- 

 vesicles contains most C0 2 and least O, and as we pass from the small to the large 

 bronchi and onwards to the trachea, the composition of the air gradually approaches 

 more closely to that of the atmosphere. Hence, if the air expired be collected in two 

 portions, the first half (i.e., the air from the larger air-passages) contains less C0 2 (3*7 

 vols, per cent.) than the second half (5 "4 vols, per cent.). The difference in the per- 

 centage of gases gives rise to a diffusion of the gases within the air-passages ; the 

 C0 2 must diffuse from the air-vesicles outwards, and the O from the atmosphere 

 and nostrils inwards ( 33). This movement is aided by the cardio-pneumatic 

 movement ( 59). In hybernating animals and in persons apparently but not 

 actually dead, the exchange of gases within the lungs can only occur in the above- 

 mentioned ways. For ordinary purposes this mechanism is insufficient, and there 

 are added the respiratory movements whereby atmospheric air is introduced into 

 the larger air-passages, from which and into which the diffusion currents of O and 

 C0 2 pass, on account of the difference of tension of the gases. 



