198 COLLECTION OF BLOOD. [BOOK 1. 



One or both the tubes having been filled with mercury and the 

 stop-cocks being shut, a narrow elastic tube leading from the 

 blood-vessel whence the blood is drawn, after being allowed to fill 

 with blood, is slipped over the free tube leading upwards from 

 the stop-cock and which is quite full of mercury. The filling bulb (R) 

 being in a suitable position, and the stop-cock opened, blood will 

 flow into the tube displacing the mercury which it previously con- 

 tained. When enough blood has been collected, the stop-cock is 

 closed, and a clip (Fig. 40) being applied to the india-rubber tube 



FIG. 40. CLIP FOB COMPRESSING INDIA-RUBBER TUBES. 



leading from the graduated tubes to the filling bulb, the tube is 

 released from the clamp which held it and shaken, or rather 

 inverted repeatedly, so as to defibrinate its contents. When fibrin 

 is separated by shaking blood and mercury in this way, it does 

 so in a state of very fine division. A suitable tube being now 

 attached to the constricted part of the graduated tube, in place of 

 that which served to conduct blood into it, and the tube having 

 been again fixed by its clamp to the stand, the mercury bulb is 

 raised, and the graduated tube^may be placed in communication with 

 the blood-receptacle of the mercurial pump, and any quantity of the 

 blood which it contains may be allowed to flow into the vacuum. 

 As the tube is graduated, the volume allowed to flow in can be 

 determined. If some time must intervene between the collection 

 of the gas and its analysis, the tube A may be removed from its clamp 

 and laid in a trough containing broken ice. 



Although other methods of collecting and measuring the blood 

 which is introduced into mercurial pumps have been employed, 

 and will be referred to. in describing the various forms of mercurial 

 pump, those here given, which the Author is in the habit of employing 

 in his laboratory, will be found to meet all requirements. 



Mercurial Pumps. 



Ludwig's The first pump to be described is Lud wig's 1 , which 



pump. wag rst fig urec i an( j described in a memoir by his pupil, 



1 The first pump to which the name of ' Ludwig ' could be applied was described by 

 his pupil Setschenow (Zeitsclir. f. rat. Med., 3rd ser., Vol. x. p. 112). The form 

 described and figured is that at present employed in the Leipzig laboratory. 



