APPENDIX 



233 



more closed and o is again lowered ; when I is thus rendered once more a 

 vacuum, k and / are opened and more of the air remaining in a, 6, d, &c. 

 rushes into the vacuum ; / is closed, j is opened, and this air is expelled as 

 before. The process is repeated as often as is necessary to make a, 6, d, &c. 

 as complete a vacuum, as indicated by the mercury in the gauge, e, as is 

 obtainable. 



a being now empty, and the stopcock, /, closed, blood is introduced by the 

 tube c ; it froths and gives forth all its gases, especially if heated to 40-45 C. 

 In the case of serum, acid has to be added to disengage the more firmly 

 combined carbonic acid. 1 The bulb, Z, is once more rendered a vacuum, and 

 k and / are opened, j being closed. The gas from a and b rushes into the 

 bulb I, being dried as it passes through d ; / is then closed and j opened ; the 

 reservoir o is raised, and as the mercury in I rises simultaneously, it pushes 

 the gases into the cylinder, /*, which is filled with mercury and inverted over 

 the end of the bent tube. This gas can be subsequently analysed. By 

 alternately raising and lowering o, and regulating the stopcocks in the manner 

 already described, all the gas from the 

 quantity of blood used can be ultimately 

 expelled into h. 



A good grease for the stopcocks is a 

 mixture of two parts of vaseline to one of 

 white wax. 



Alvergniat's pump has the advantage 

 over Pfliiger's of fewer connections, and 

 all of these are surrounded by mercury, 

 which effectually prevents leakage ; it has 

 the disadvantage of a rather small bulb 

 in place of I, and thus it is more labour to 

 obtain a vacuum. 



Leonard Hill's pump. This is a simpler 

 instrument, and is sufficient for most 

 purposes. It consists of three glass bulbs 

 (B.B. in fig. 80), which we will call the 

 blood bulb ; this is closed above by a 

 piece of tubing and a clip, a ; this is 

 connected by good india-rubber tubing to 

 another bulb, d. Above d, however, 

 there is a stopcock with two ways cut through 

 which B.B. and d may be connected, as in the figure ; and another seen 

 in section, which unites d to the tube e, when the stopcock is turned through 

 a right angle. In intermediate positions the stopcock cuts off all communi- 

 cation from d to all parts of the apparatus above it ; d is connected by tubing 

 to a receiver, R, which can be raised or lowered at will. At first the whole 

 apparatus is filled with mercury, R being raised. Then, a being closed, R is 

 lowered, and when it is more than the height of the barometer (30 inches) 

 below the top of B.B. the mercury falls and leaves the blood bulb empty ; by 

 lowering R still further, d can also be rendered a vacuum. A few drops of 



1 Phosphoric acid is usually employed. 



B.B 



FIG. 80. L. Hill's air-pump. 



one by means of 



