2 4 2 



TEXT-BOOK OF PHYSIOLOGY 



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 0.5 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 end, M, of the rubber 

 tube into the mouth. The tube is then quickly inserted into a solution 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, 1 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. 94 shows both a surface view, a, and a section view, b, of the counting 

 chamber. This consists of an oblong glass plate, o, on which are cemented two 

 small pieces of glass, one of which, WD, has in the center a circular opening 

 in which is placed the other, B, a circular disc or stage. Their relation is such 

 that a narrow groove or moat separates the one from the other, the floor of which 

 is formed by the glass plate. The surface of the circular stage is exactly o.i mm. 

 lower than that of the cover-glass, r. On the surface of the glass stage a series 

 of small squares is engraved, C, each one of which has a side length of ^ mm. 

 and an area of ^ square mm. To facilitate counting, a group of 16 such 

 squares is surrounded by a thick line. Fig. 95. This group is separated from 



adjoining groups, also enclosed by thick lines by 

 an intermediate fine line, which serves as a guide 

 in passing from one group to another. When a 

 cover-glass is accurately applied to the glass, b, 

 each one of the small squares will have a cubic 

 capacity of ^^Xo.i, or ffa-Q cubic millimeter. 



Before placing the diluted blood on the count- 

 ing stage, the fluid in the tube of the pipette 

 should be blown out and discarded, as it contains 

 no portion of the blood. A small drop is then 

 placed on the glass stage and covered with the cover- 

 glass. After a few minutes the corpuscles settle 

 upon the ruled spaces and are ready for counting. 

 The number of corpuscles in at least five series 

 of sixteen small squares is then counted; this 

 number is then multiplied by the degree of dilu- 

 tion (100 or 200 as the case may be) and this divided by the cubic contents 

 of each small square (^oVg-) ; the product is then divided by the number of squares 

 counted (80 in the instance given above): e.g., five series of sixteen small squares 

 contain 500 corpuscles 



50oX2 X4000 = 5,ooo,ooo erythrocytes per c.mm., 



The accuracy of the counting is proportional to the number of squares counted. 

 If 200 squares are counted with each of two different drops, and the average taken 

 the probable limit of error will be less than 2 per cent. 



Various solutions have been devised for diluting blood, any one of which may be employed, e.g.: 



FIG. 95. MICROSCOPIC AP- 

 PEARANCE OF THE SMALL 

 SQUARES AND THE DISTRIBU- 

 TION OF THE CORPUSCLES. 



Hayem's Fluid: 



Hydrarg. bichlor 0.5 gm. 



Sodii sulphat 5 .o gm. 



Sodii chlorid 2.0 gm. 



Aquae destillat 200 .o gm. 



Gower's Fluid: 

 Sodii sulphat 

 Acid, acetic 



Toisson's Fluid: 



Aquae destillat 160.00 parts. 



Glycerinae 30 .00 parts 



Sodii sulphat 8 .00 parts. 



Sodii chlorid i .00 part. 



Methyl- violet 0.025 part. 



fi 



104 



Aquae dest q. s. ad giv. 



