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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the blood, so that, notwithstanding a smaller volume per cent, of CO 2 in the 

 lymph, CO 2 passes to the blood because of the higher tension in the lymph. 



Extraction of Gases from the Blood. We have found that in the blood 

 both O and CO 2 exist partly in solution and partly in chemical combination. 

 The portion in solution comes off regularly with a diminution of pressure, but 

 that which is in chemical combination remains so until the pressure is reduced 

 to the level of the tension of dissociation. Since there are several of these 

 combinations, such as O in oxyhaemoglobin and CO 2 in carbonates, bicarbon- 

 ates, alkali phosphates, etc., portions of each of these gases come off at different 

 pressures in accordance with their different tensions in the several chemical 

 combinations. The portions in solution may be removed by the use of an 



ordinary air-pump, but those in 

 chemical combination are held so 

 firmly that the more powerful mer- 

 curial pump is required. A con- 

 venient pump of this kind has been 

 devised by Dr. Geo. T. Kemp, the 

 description of which he gives as 

 follows : 



" To use the pump the reservoir 

 bulb Bb (Fig. 136), the bulb 7, the 

 cylinder SR and S'R' , and the ves- 

 sel Pare filled with mercury. When 

 the bulb Bb is raised the mercury 

 rises in the tube AC and fills B, 

 driving the air out by the path 

 FHOP, the stopcock Q being closed. 

 When Bb is lowered again the mer- 

 cury flows back from B into Bb, 

 creating a Torricellian vacuum in 

 B. As soon as the mercury has 

 fallen below the joint D, this 

 vacuum in B becomes connected 

 by the path LEG with the tubes 

 TOUG'T' and the tube VWYX. and 



FIG. 136. Kemp's gas pump. , . 



thence, when the stopcock is open, 



with the vessel to be exhausted. The air in this then diffuses to fill the 

 vacuum in B, and becomes rarefied, so that the mercury rises from the cylin- 

 ders SR and S'R 1 in the -outer tubes TO and T'G'. The small inner tubes 

 RG and R'G' are made so high that even when there is a complete vacuum in 

 the outer tubes TG and T'G' the mercury will not rise high enough to cover 

 them. 



"On raising Bb again the mercury rises in AC, and as soon as the joint D is 

 covered, all the air which has been caught in B is forced out by the path FHOP. 

 Each time the bulb Bb is raised and lowered a certain amount of air is ex- 



