202 PFLUEGER'S MERCURIAL PUMP. [BOOK i. 



into the chamber, the stop-cock G is shut, the globe D is elevated, 

 and by a suitable movement of the stop-cock the imprisoned gas is allowed 

 to pass either into the air, or is collected through H over mercury in 

 the graduated tube K standing in the pneumatic trough /. By repeating 

 several times the series of operations described the amount of residual 

 gas in the apparatus sinks to an insignificant amount, and, without 

 great labour, a practically perfect vacuum is obtained. 



The accessory apparatus shewn in the drawing requires description. 

 is a mercurial gauge, B is the drying chamber, composed of four 

 glass tubes communicating below with two small reservoirs. The tubes are 

 filled with pumice-storie or asbestos saturated with sulphuric acid, and the 

 bulbs also contain some of the same acid. The drying- chamber is in 

 communication with two large glass bulbs A, which are intended to arrest 

 the froth which arises from the boiling blood. To the 'froth-chamber' 

 is carefully attached a glass bulb M, into which the blood is placed. 

 This bulb has at its upper part a single-way stop-cock, but below it 

 is provided with a two-way cock. The plug of the stop-cock is, in the 

 drawing, shewn to be prolonged considerably beyond the socket into 

 which it fits. This plug is perforated in its long diameter by a canal 

 which passes through it obliquely, and is so arranged that the fluid passing 

 through the canal may be directed upwards into the 'blood-bulb,' or 

 downwards and outwards. (Fig. 43.) 



A vacuum having been made in the 'drying-chamber,' the 'froth- 

 chamber,' and the 'blood-bulb,' the plug of the lowest stop-cock of the 

 blood-bulb (a, Fig. 43) has attached to it, by means of a piece of thoroughly 

 sound black elastic tube, a flexible metallic tube, which is connected peri- 

 pherally with a glass cannula which is tied into the blood-vessel whence the 

 blood is to be drawn, or preferably with a blood-measuring tube. 



Blood is now allowed to flow through the elastic tube until the latter is 

 filled, the plug being placed in such a position that the displaced air 

 and the displacing blood flow at first not into the blood-bulb but outwards. 

 At a given moment the stop-cock is turned (in the position shewn in Fig. 43) 

 so as to open a communication between the blood-bulb and the blood- 

 measuring tube, or the blood-vessel: the blood flows into the vacuous 

 bulb, and immediately enters into ebullition. As soon as enough blood 

 has entered, the lower stop-cock is shut, and the stop-cocks which shut 



FIG. 43 exhibits the construction of the two-way cock (., Fig. 42) at the lower part 

 of the blood-bulb. When the plug is in the position shewn the tuhe a communi- 

 cates with the interior of the bulb. "When the position is reversed a communicates 

 with 6. In intermediate positions the bulb is shut off and the tubes a and b do not 

 communicate. 



