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TEXT-BOOK OF PHYSIOLOGY. 



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, a. On the surface of the glass stage a series of small squares 

 is engraved, each one of which has a side length of -fa mm. and an area 

 of i square mm., B. To facilitate counting, a group of 16 squares is 



surrounded by a heavy 

 dark line. This group is 

 separated from adjoining 

 groups, also enclosed by 

 dark lines, by an inter- 

 mediate light line, which 

 serves as a guide in pass- 

 ing 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 

 4-^ X o.i, or ^Vo cubic 

 millimeter, and every four 

 such squares will have 

 therefore a capacity of 

 T oVo cubic millimeter. 



Before placing the di- 

 luted blood on the count- 

 ing stage, the fluid in the 

 tube of the pipette should 

 be blown out and dis- 

 carded, as it contains no 

 portion of the blood. A 

 few drops are then placed 

 on the glass stage and 

 covered with the cover- 

 glass. After a few min- 



FIG. 99. -^-APPARATUS OF THOMA AND ZEISS 

 FOR COUNTING THE CORPUSCLES. A. In 

 section. C. Surface view without cover- 

 glass. B. Microscopic appearance with the 

 blood-corpuscles. (Landois and Stirling.} 



utes the corpuscles settle 

 over the ruled spaces and 

 are ready for counting. 

 The number of corpuscles 

 in a horizontal series of 4 



squares is then counted; this number is then multiplied by 1000 in order 

 to get the number in i cubic millimeter of the diluted blood, and this 

 product by 100 or 200 according to the extent of the dilution: e. g., four 

 squares contain 50 corpuscles; multiplied by 1000 and then by 100 

 5,000,000. The accuracy of the counting is proportional to the number 

 of squares counted. If 200 squares are counted and the average taken, 

 the probable limit of error will not be more than 2 per cent. 



Effects of Reagents on the Red Corpuscles. Within the 

 blood-vessels the composition of the plasma is such that both the 



