274 LA BORA TOR Y GUIDE JIV PHYSIO LOG Y. 



that may be on the outside of the tube. Plunge it into 

 the well of water, shaking it back and forth to thor- 

 oughly mix the blood and water. With the medicine 

 dropper wash the tube with a few drops of distilled 

 water; then remove the tube and draw the solution in 

 and out of the dropper several times to be sure it is 

 well mixed. Then fill both compartments to the brim 

 with the dropper, taking care that the mixture of blood 

 and water shall not flow over into the pure water. Ex- 

 clude daylight, and by artificial light adjust the compart- 

 ment containing clear water, so that it comes over the 

 slip of colored glass. Adjust the reflector so that light 

 is thrown up through the well. Then adjust the slip of 

 colored glass until it corresponds with the color of the 

 diluted blood and read the amount indicated by the 

 scale. This will give the percentage of haemoglobin, 

 100 being the standard for normal blood. 



Any approximate success with this instrument pre- 

 supposes a color sense. Even when this is present in 

 the student, the instrument itself is not entirely reliable 

 as there is sometimes a variation in the colored slips of 

 glass. It is also not reliable for percentages of haemo- 

 globin under 20. 



4.. Precautions. The capillary tube should be cleaned by 

 drawing through it a thread wet with alcohol and ether. 

 The tube must be filled and emptied quickly to prevent 

 coagulation. In reading the instrument, do not face 

 the light but let it come from the side. The instrument 

 should be so placed that the wedge will not move from 

 left to right but to and from the operator. Use as little 

 light as possible. Use first one eye and then the other. 

 Move the screw with quick turns rather than a gradual 

 motion, as the impression of a glance is better than a 

 prolonged look. 



