156 THE BLOOD 



as Fleischl's hemometer, see figure 122. The principle of this instrument 

 rests on a comparison of the color of the sample of dilute blood with a stand- 

 ard glass wedge of uniform tint similar to that of blood. Fill one of the 

 chambers in the cells of the instrument half full with a 2 per cent, solution of 

 sodium carbonate. Now draw a drop of blood from the tip of a finger. 

 Touch the drop with the end of the standardized capillary tube, using care 

 to fill it accurately. Quickly wash this sample of blood out in the carbonate 

 solution in the cell and finish filling the cell. Put distilled water in the other 

 half of the cell, mount in the instrument, and examine in a dark room, using 

 candle-light. The glass wedge is graduated in percentage which can be 

 read off directly. This instrument is usually provided with several cells, in 

 which case as many samples may be taken and the average of the readings 

 used to determine the percentage. 



Perhaps a more convenient and certainly a quicker method for deter- 

 mining the percentage of hemoglobin is Talquist's hemoglobinometer. By 

 this method a drop of blood is drawn directly on to absorbent-paper furnished 

 with the instrument, and the resulting stain is compared directly with a paper 

 color scale which is graduated in percentage. In this method the comparison 

 is made in ordinary daylight, and because of its rapidity it is very convenient 

 for clinical examinations. 



7. Reaction of Blood Plasma. Wet a piece of red litmus-paper in 

 saturated magnesium sulphate solution, then touch one end of the strip wdth 

 a drop of blood drawn from your finger under sterile conditions. After a. 

 few moments wash off the excess of corpuscles in neutral distilled water. 

 The blue at the point of contact with the blood indicates alkalinity. 



8. The Specific Gravity of Blood. From standard mixtures of 

 chloroform and benzol with specific gravity of i .050, i .060, and i .070 make 

 up a set of specific-gravity solutions of 1.050, 1.052, 1.054, etc., to 1.070, 

 These standards may be kept in stoppered 4-dram vials, or in test-tubes. 

 The specific gravity of blood is determined by inserting with a pipet a 

 drop of freshly drawn blood into the middle of one of the solutions, say 

 i .056. Since the blood does not mix with the chloroform and benzol, the 

 drop will rise or sink according to its relative specific gravity. By a few 

 trials one may quickly find a specific gravity in which the drop of blood 

 floats without rising or sinking. This represents the specific gravity of the 

 drop of blood. 



This method permits rapid clinical application and has proven of con- 

 siderable interest in the hands of clinicians. 



9. The Isotonicity of Blood. The absorption or loss of water 

 by the corpuscles of blood in solutions of other concentrations than that of 

 blood plasma can be used as a means of determining the isotonicity of blood. 

 Make up a series of solutions of sodium chloride, varying by tenths, from 

 o . 5 to i . 2 per cent. Prepare a series of slides with vaselin rings and mount 



