144 THE BLOOD 



cell should be multiplied by f to bring it up to that of the larger. For example, 

 suppose the result of several readings to be: 



With the large cell (15 mm.) 54 . oo 



With the small cell (12 mm.) 42 .00 



If the readings obtained with the large cell are exactly correct, then the read- 

 ings with the smaller one should be 43.2, since 54 X =43.2. Or, if the 

 readings with the smaller cells are exact, the readings with the larger should 

 be 52. 5, since 42 Xf =52.5. Hence the mean of 54 and 52.5, namely 53.25, 

 should be taken as the correct figure. On looking at the corrected table of 

 hemoglobin values supplied with each instrument, we would find that this 

 number on the scale corresponds to a solution containing 400 milligrams 

 of hemoglobin per 1000 cubic centimeters of solution. But our original dilu- 

 tion was either i : 200, i : 300, or i : 400, according as our pipet had been 

 filled with blood up to the mark -}-, , or J; so that in order to obtain the actual 

 percentage of hemoglobin in the blood under examination we should be 

 obliged to multiply our results by 200, 300, or 400. In the example we have 

 taken, the amount of hemoglobin would be, if our dilution was i : 200, 400 X 

 200=80,000 milligrams = 80 grams in 1,000 cubic centimeters = 8 grams 

 in 100 cubic centimeters, or 8 per cent. 



The Dare's hemoglobinometer avoids the error of diluting blood by 

 comparing undiluted blood under artificial light with a colored scale which 

 is graduated after standardization against a hemoglobin content of normal 

 blood, i.e., 13.77 grams of hemoglobin per 100 cubic centimeters. The 

 instrument, see figure 1220, consists of a blood pipette, a case inclosing the 

 color comparison disc, and is provided with a small telescope for reading 

 the color contrasts against an artificial candle light. A drop of blood is 

 drawn with a lancet from a finger tip or the lobe of the ear, is allowed to 

 run directly between the plates of the pipette where it spreads by capil- 

 larity. The gradations on the comparison scale are read under candle 

 light and the computations for the percentage of hemoglobin in the sample 

 made against the normal. Its ease of manipulation and comparative 

 accuracy gives to this method the status of a clinical favorite. Another 

 clinical method somewhat less readily manipulated is that of Sahli. 



The Talquist method enables one to make a quick approximation of 

 the hemoglobin content. It is valuable as a preliminary test to the Dare 

 and is sufficiently accurate for many clinical determinations. 



This consists of a series of shades of color corresponding to undiluted 

 blood of various hemoglobin values, ranging from 10 to 100 per cent, of an 

 arbitrary scale. This scale is included in a book, the remaining pages of 

 which consist of filter-paper, which is used for absorbing the specimen of 

 blood whose hemoglobin percentage is to be estimated. The blood- 

 stained filter-paper is compared with the hemoglobin scale by direct day- 



