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N: 



BAIRD &TATLOCK. (LONDON) LTD. 



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843 



844 and 845 



magnified 20 times. 



Cross-line division alter Thoma. 



844 



Cross-Hue uivuion 



845 



843' 



Thoma's Haemacytometer, by Zeiss. This apparatus consists of counting chamber in 

 combination with an accurately calibrated mixing pipette for diluting the blood in a certain 

 ratio (i : 100 for red, I : 10 for white corpuscles), with directions for use. 



A. In case, with mixing pipette for red corpuscles . . each 



B. white 



C. ,, with both pipettes 



Pipettes separately 



D. For red corpuscles (diluting i : 100) 



E. For white corpuscles (diluting i : 10) 



A drop of blood is drawn from the linger by a lancet-shaped needle, and the point of the mixing pipette is 

 jlaced iu it, and the blood is aspirated into the capillary tube as far as the division marked i. The tra. 

 )lood on the point of the pipette are removed, and the point is dipped into Hayem's fluid, which consists of 

 I part of sodium chloride, 5 parts of sodium sulphate, 0.5 part of corrosive sublimate, and 200 parts of distilled 

 water. This fluid is sucked up until the diluted blood reaches the mark 101, and then the tip of the mouth-piece 

 s closed with the finger, and the contents of the bulb are mixed by shaking. The contents of the capillary 

 stem at this stage do not enter into the bulb, it therefore follows that the bulb contains a mixture of 99 parts 

 ot I l.ivem's fluid and I part of blood. The observer now gently blows through the mouth-piece, and the fluid 

 in the capillary portion of the pipette and the first few drops of the contents of the bulb are rejected. The 

 next drop is placed upon the centre of the counting chamber, the cover slip is placed upon the surface of the 

 outer cell, and the counting chamber is placed upon the stage of the microscope, and left for a few minutes 

 to allow the corpuscles to settle. Each square of chamber covers an area of 1-400 square millimetre, and h.i-- 

 a volume of 1-4000 cubic millimetre, therefore i cubic millimetre contains 4,000 times the average number of 

 a square. The dilution was i : 100, therefore : average in a square X 4,000 X 100 = number of corpusi -Ir-. 

 iu i cubic millimetre of blood. 



844' Counting Chamber, after Thoma, as in No. 843, depth of chamber o.ioo mm. Price, in case 



845' Counting Chamber, alter Zappert, the outer squares divided into four squares. Price, in 

 case . . . . . . . . . . each 



1 

 1 

 1 





 



14 



14 6 



.CHEMICAL AND SCIENTIFIC APPARATUS AND PURE CHEMICALS. 



m 



175 



