210 THE BLOOD. 



orifice of the tube, and both stopcocks are opened. The blood 

 passes rapidly into the recipient, followed by a column of mer- 

 cury, and is at once converted into froth. A few drops of mer- 

 cury having been allowed to enter, the stopcocks are finally 

 closed. It will be understood from the figure that the joint 

 between the measuring tube and the recipient, as well as the 

 stopcocks, are under water, the purpose of which arrangement 

 is, it need scarcely be said, to obviate the risk of the entrance 

 of air. 



At first the water in the wooden trough (N, which is not in- 

 troduced until M has been joined to L) is kept cool with frag- 

 ments of ice, in order to prevent the blood from coagulating 

 during the preliminary operations. As soon as all is complete, 

 hot water is gradually added until the temperature rises to 

 about 40 C., care being taken not to expose the stopcocks to 

 the air during the process. The only moment in the process 

 at which air can be admitted, is that of joining the measuring 

 tube to the recipient. For this reason it is desirable, before 

 opening the second stopcock of the measuring tube, to keep the 

 pump in action for a few minutes so as to be certain that the 

 vacuum is unimpaired before admitting the blood. This is not 

 attended with inconvenience, if the blood is kept at a tempera- 

 ture approaching that of freezing. 



When it is desired to defibrinate the blood before exhausting 

 it, it must be collected over mercury. This is best effected in 

 Ludwig's recipient. This recipient is a tube closed at one end 

 and furnished with a Geissler's stopcock having a remarkably 

 large way. The tube is inverted over mercury, with the stop- 

 cock open, and the blood allowed to flow directly from the ves- 

 sel into it until it is nearty filled. It is then closed by the hand, 

 defibrinated by vigorous shaking with mercury, and replaced 

 in the trough. The stopcock is now closed, and the tube, from 

 which the blood contained outside of the stopcock has been 

 washed, is united with the recipient of the pump by an India- 

 rubber joint. To carry out this method, Sprengel's pump is 

 scarcely applicable ; for, inasmuch as the process of exhaustion 

 cannot be begun until the connection is made, a longtime must 

 elapse before the tap can be opened. Blood alters so rapidly 

 after removal from the body the oxygen diminishing, the car- 

 bonic acid increasing that if much time is lost the results are 

 of little value. 



30. Method of Analysis. In France most of the analy- 

 ses which have been published by Bernard and his pupils have 

 been made by a method which, although rapid, is inexact. In 

 Germany the analyses of Ludwig and his pupils, as well as 

 those of Pfliiger, have been made according to the accurate 

 methods first introduced by Bunsen, and commonly known by 

 his name. Bernard's method is practised in the physiological 



