204 ALVERGNIAT'S MERCURIAL PUMP. [BOOK i. 



into the lower of the two large bulbs, which are attached to the pump, and 

 which have been perfectly exhausted. 



The quantity of blood analysed is determined after the gases have been 

 extracted by weighing the bulb apparatus (Fig. 44), and the sulphuric acid 

 drying apparatus, and subtracting the weight of the same, as determined 

 before the blood was boiled. It is obvious that with this pump also it is 

 easiest to measure the blood before it is introduced into the vacuum. 



The special features of the process described above, and which 

 renders it preferable to some others employed for the same purpose, 

 are, (1) the blood may readily be brought directly (if desired) without 

 previous defibrination, from the blood-vessels into the apparatus 

 where its gases are separated : in this respect it differs, for instance, 

 from Lud wig's pump ; (2) the blood is at once introduced into a very 

 large vacuous space, so that the O-pressure outside the blood is always 

 very much below the dissociation -tension of the of the blood, 

 the latter therefore escapes very rapidly; (3) the vacuum is main- 

 tained in a dry condition by the sulphuric acid in the drying chamber ; 

 this appears to have very great influence in facilitating the removal 

 of the gases from the blood. With such an arrangement it is possible, 

 for instance, in a very brief space of time rapidly to extract all the 

 carbonic acid of the blood without the necessity of adding a dilute acid. 



Alver- This pump, constructed by MM. Alvergniat freres 



gniat's pump. o f p ar i Sj was fi rs t employed in the investigation of the 

 gases of tbe blood by Orphan t and Bert 1 , and bas already proved most 

 useful. Being constructed exactly on the principle of Pfluger's pump, 

 it does not require a special description ; it will be observed that its 

 barometric chamber is very much smaller than that of the first-named 

 instrument, and that it is not, as sold, provided with any arrangement 

 for absorbing watery vapour which may be given off in vacuo, though 

 such an arrangement can be contrived and connected with it by the 

 operator. The special features of this pump are, 1st, that just above 

 the three-way cock is situated, permanently, a most convenient 

 small mercurial trough, 2ndly and chiefly, that the three-way cock is 

 immersed in an iron box which is filled with mercury, so that all 

 risk of leakage is avoided. 



In extracting the gases of the blood with this small pump it is 

 usual to connect with it a long glass tube about 2 inches in diameter, 

 with a bulb blown at its lower end having a capacity of about one litre. 

 This bulb is closed by an india-rubber stopper which is perforated by a 

 thermometer tube of narrow bore. The junction between the tube 

 and the pump is made by means of india-rubber tube carefully wired, 

 and is protected by a water-joint. The bulb also is immersed into a 

 tin vessel containing water. The narrow thermometer tube has 

 attached to it a fine glass stop-cock with an almost capillary bore. 

 This stop-cock is also immersed in water. This system of protecting 

 every junction by surrounding it either with water or mercury is un- 



1 Bert, Lemons sur la Respiration. Paris, 1870. 



