CHAP. IV.] THE BLOOD. METHODS OF RESEARCH. 215 



of caustic potash of sp. gr. 1-2, taking care that not a trace of air be 

 introduced ; by unclampin& the tube and alternately raising and depressing 

 the tube in the mercury the absorption of CO 3 by the caustic potash is much 

 facilitated. After absorption appears to be complete, the tube is again 

 adjusted, so that the level of mercury inside and outside is the same, and 

 the volume of gas determined as before. If we subtract this volume from 

 that of the original gas the amount of carbon dioxide is ascertained. 



About half a c.c. of a strong solution of pyrogallic acid (1 part 

 of acid to 8 of water) is now introduced into the tube, and the process of 

 shaking, &c., repeated. After the oxygen is absorbed the absorption tube 

 is transferred to a vessel containing water, and the level of the liquid 

 inside and outside of the tube being the same, the volume of gas is read 

 as before; the gas consists entirely of nitrogen, and by subtracting its 

 amount from that of the gas remaining after the absorption of CO 2 , we 

 determine the quantity of oxygen which was present. 



It will be apparent to the reader that carried out as above there are 

 certain inherent errors which it is not easy to eliminate ; the method may 

 be rendered more accurate, however, by absorbing the carbonic acid by a 

 ball of caustic potash fused on platinum wire, then, after determining 

 the volume, absorbing the oxygen by solution of caustic potash and 

 pyrogallic acid, and after complete absorption transferring the tube which 

 contains the residual gas to a trough containing water, and reading the 

 nitrogen over water; or, again, after absorption of the C0 2 by the ball 

 of caustic potash, the oxygen may be absorbed by a bullet of phosphorus 

 left in the gas for 24 hours ; in this case, however, before reading off the 

 volume, a bullet of caustic potash must be introduced into the gas and left 

 for some hours, and the residual gas read as dry. 



Determination of the total quantity of blood contained in an 

 animal's body. 



Weicker's A tube is tied into the carotid of the animal 



whilst yet alive, and a few cubic centimetres of blood 

 collected, defibrinated, measured, and set aside (portion A). The 

 animal is then bled to death, the whole of the blood defibrinated and 

 kept (portion B). The blood-vessels are then washed out with 

 normal salt solution until the washings issue quite colourless ; these 

 are added to portion B, and tbe whole mixed and measured. Some 

 of the red solution thus obtained is placed in a liaematinometer, 

 which we shall designate as H.B. ; a small quantity of A is then 

 diluted with 10 times its volume of distilled water, and an accurately 

 measured volume (one or two cubic centimetres) is placed in a 

 second haematinometer (H.A.) placed by the side of the first and 

 illuminated in exactly the same manner. 



Distilled water is now added from a burette to the contents of 

 H.A. until their tint is exactly equal to the fluid in H.B. ; when 

 equality is obtained, the volume of water added is read off, and thus 

 is found the volume of the solution of pure blood which was equal to 

 the previously unknown mixture of portion B and washings. By 

 simple calculations, of which the steps are perfectly obvious, we can 



