ESTIMATION OF THE AMOUNT OF HEMOGLOBIN 233 



other (d) : the latter fits over the pointed end of the capillary 

 tube mentioned first; and (6) a small wax candle such as is 

 used for Christmas-trees. A camera-tube lined with a green 

 material is used to screen the eyes whilst the comparison is 

 being made. 



Method of Use. Prick the patient in the usual way. Apply 

 the polished end of the capillary tube to the drop of blood : 

 this will completely fill the tube, being drawn up by capillary 

 attraction. When quite full, wipe both ends of the tube with 

 the fingers, and apply the end of the glass pipette (previously 

 filled with water) to the pointed end of the capillary tube. 

 Now squeeze the nipple gently, so as to force the blood and 

 (subsequently) the water drop by drop into the cell. Inter- 

 rupt the process occasionally, and stir the contents of the 

 cell with the metal handle of the measuring tube. Continue 

 to add water until the cell is exactly full : this is the first step 

 which presents the slightest difficulty. Apply the cover- 

 glass; this must not enclose any air under it, nor cause any 

 of the diluted blood to flow into the moat round the cell. 



The specimen is now ready for comparison with the 

 standards. It is to be taken into a dark room and examined 

 by the light of one of the candles. This is to be placed in 

 front of the observer at a short distance from the specimen 

 and standard, which must lie side by side. 



The viewing is best done by means of a camera-tube which 

 folds into the box containing the whole apparatus. It ter- 

 minates in a diaphragm which is perforated 'by two small 

 holes, one of which is to be placed over the centre of the 

 specimen and the other over the centre of the standard. The 

 latter is to be moved about until a disc is found which nearly 

 or quite corresponds in colour with the diluted blood in the 

 cell. If the correspondence is exact, the process is at an end; 

 the number ag'ainst the disc in question represents the per- 

 centage amount of haemoglobin. If there is no disc which 

 exactly matches the specimen, the latter is placed against 

 the disc which is nearest to it, but not so deep in colour. 

 For example, if we found .that the specimen was darker than 

 the disc numbered 50, but paler than that numbered 60, then 

 it would be placed opposite to 50. A slip of colourless glass 

 is then applied over the specimen, and riders over the 

 standard disc, until an exact match is obtained. If, in the 



