334 



RESPIRATION 



A very important advance in our knowledge of the blood gases was made 

 by the introduction of the Torricelli vacuum for the purpose of extracting 



them. This method was first used by 

 Ludwig (1859), after Collard, de Mar- 

 tigny, and Hoppe-Seyler had tried it 

 for other purposes. Since that time it 

 has been improved in many ways by 

 many different authors (Fig. 130). 



1. ABSORPTION OF GASES IN 

 LIQUIDS 



When a liquid stands in contact with 

 a space filled with gas, the gas passes 

 from the space into the liquid until the 

 latter has taken up as much gas as the 

 conditions will permit. We must distin- 

 guish clearly between two of these con- 

 ditions. 



A. The liquid exercises no chemical 

 attraction upon the gas. In this case the 

 amount of gas absorbed depends upon 

 three factors : (1) the nature of the liquid 

 and the gas, (2) the temperature, and (3) 

 the pressure to which the gas is subjected. 

 We may formulate the facts in the follow- 

 ing law: The volume of a gas absorbed 

 under different pressures by a given liquid, 



FIG. 130. Schema of Ludwig's pump for 



extraction of the blood gases. The when reduced to the same pressure and 

 pump consists of two bulbs C and D con- temperature, is proportional to the pres- 



nected by rubber tubing with the mer- 

 cury bulbs A and B. When the stop- 

 cocks a, 6, c, d are opened and the bulb 

 B is raised, the bulbs C and D are filled 

 with mercury. Then if the stopcock c 

 is closed and the bulb B lowered until volume of the liquid under a pressure of 



sures (Law of Henry). 



The coefficient of absorption is the vol- 

 ume of the gas (reduced to and 760 

 Hg.) which is absorbed by a unit 



the difference in level between B and C 

 is greater than barometric pressure, a 

 Torricelli vacuum is created in C. When 

 C is empty of mercury a is closed. Then 



760 mm. 



When several gases within the same 

 space are brought in contact with a liquid, 



if a vessel containing blood, which has tne absorption of each is quite independ- 

 ent of the others, and depends only upon 

 that pressure which the gas itself exerts 

 (Law of Dalton). 



This partial pressure of each gas can 

 be calculated, if the total pressure exerted 

 by the mixture and the composition of the 

 mixture are known. It is always that 

 percentage of the total pressure, repre- 



not been exposed to the air, but has been 

 drawn directly from an artery or vein, 

 is connected with 6, the contained gases 

 will bubble off into C. By suitable 

 manipulations, which may be readily 

 understood from the figure, the gases 

 are transferred to D and finally to the 

 graduated burette E, where they are 

 measured. 



sented by its volume percentage of the 



mixture. For example: Water is in contact with air under a pressure of 

 760 mm. Hg. Air consists of 21 vols. per cent of oxygen, and 79 vols. per cent 



