214 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



seven, and in this case you can count 104 fields and multiply by 

 100, or 52 and multiply by 200. 



Wiiere very great accuracy is required the special diluting 

 pipette should be used.* 



All the steps are similar to those just described at full length, 

 except that a different diluting fluid is used. 



The diluting fluid is one which destroys' (" lakes") the red 

 corpuscles, but does not injure the leucocytes. It consists of a 

 0-3 or 0-5 solution of acetic acid (glacial) in water ; it is better to 

 add a small quantity of methyl violet or gentian violet, so that the 

 leucocytes are stained and thereby rendered more prominent. 

 This solution is best prepared fresh, or at any rate kept in a well- 

 stoppered bottle. 



The pipette is distinguished from that used for the red cor- 

 puscles by its having the number 11 above the bulb. This 

 indicates that if blood be sucked up to the mark i below the bulb, 

 and diluting fluid up to the transverse mark above the bulb, the 

 dilution will be i in 10, and so on. 



The blood should be sucked up to the mark i if a great excess 

 of leucocytes is not expected. If the case is one of leucocytosis, 

 a greater dilution is better ; whilst if there is a great excess of 

 leucocytes (such as occurs in severe leucocythasmia) , it is best to 

 use the red corpuscles pipette with a dilution of i in 100, but 

 employing the acetic acid diluting fluid. Then proceed to make 

 the preparation, and count by the field method as above. 



deeming the Hamocytometer Pipettes. — Immediately after use the 

 pipettes must be thoroughly cleaned. The fluid which remains 

 in the bulb must be blown out, and for this purpose, as well as 

 for the subsequent washings, it is an advantage to reverse the 

 position of the indiarubber tube, so that the fluid may be blown 

 out through the upper part of the pipette, this being the wider. 

 The whole pipette must now be filled with water (preferably 

 distilled), and the water blown out. This process is repeated, 

 using absolute alcohol, and allowing it to run out of the pipette 

 without blowing it. Lastly, fill the whole pipette with ether, 

 remove the indiarubber tube, replace it with the tube of an 

 ordinary spray (such as is used for scent fountains, throat sprays, 

 etc.), and pump air through until the apparatus is absolutely dry. 



* I allow this statement to stand, but have now great doubts as to its 

 correctness, and believe that the results obtained by the field method are 

 even more accurate, especially in unpractised hands. 



