THE BLOOD. 



239 



Welcker has been modified by different observers, and especially by 

 Thoma and Zeiss. On account of the great number of corpuscles 

 in i cubic millimeter of blood, it becomes necessary for purposes of 

 enumeration that the blood be diluted a definite number of times and 

 that the diluted mixture be placed in a counting chamber possessing 

 a definite capacity. By means of the pipette or melangeur of Potain 

 and the counting chamber of Thoma both these objects are attained. 



The pipette consists of a capillary tube (Fig. 98) A 



provided with an enlargement containing a freely mov- 

 able small glass ball, a. One end of the tube is pointed, 

 while to the other end is attached a rubber tube for the 

 purpose of facilitating the introduction of the blood 

 and the diluting fluid. The capillary tube, which is 

 accurately calibrated, carries marks, J, i, 101, which 

 signify that if the tube be filled with blood up to the 

 mark i and the diluting fluid be sucked into the 

 tube up to the mark 101, the blood will be diluted 

 100 times. If the blood be sucked up to the mark 

 J and the diluting fluid to 101, then the blood will 

 be diluted 200 times. In using the pipette the point 

 is introduced into a drop of blood derived from a 

 small wound in the skin of the lobe of the ear or 

 finger and sucked into the tube by introducing the 

 rubber tube into the mouth. The tube is then 

 quickly inserted into a solution, similar in specific 

 gravity to the plasma, which will preserve the shape 

 and size of the corpuscles, such as Gowers's sodium 

 sulphate solution, sp. gr. 1.025, or a 3 per cent, 

 sodium chlorid solution,* and the fluid sucked into 

 the tube up to the mark 101. On shaking the 

 pipette for a few minutes, the admixture will take 

 place, aided by the movements of the glass ball. 



Fig. 99 shows both a section view, A, and a 



FIG 



. !. MELAN- 

 GEUR OR PIPETTE. 

 (Landois and 

 Stirling.} 



surface view, C, of the counting chamber. This con- 

 sists of an oblong glass plate on which are cemented 

 two small pieces of glass, one of which has in the 

 center a circular opening in which is placed the other, a circular disc or 



* Various solutions have been devised for diluting blood, any one of which may 

 be employed, e. g.: 



Toisson's Fluid: 



0.5 gm. Aquae destillat., 160.00 parts. 



5.0 " Glycerinse, 30.00 " 



2.0 " Sodium sulphate, __ 8.00 " 



200.0 " Sodium chlorid, i.oo " 



Methyl-violet, 0.025 part. 



Hayem's Fluid: 



Hydrarg. bichlor., 



Sodium sulphate, 



Sodium chlorid, 



Aquae destillat., 



Gowers's Fluid: 



Sodium sulphate, gr. 104 



Acid, acetic., 3J 



Aquae dest., q. s. ad giv. 



