2OO MICROMETRY AND BLOOD PREPARATIONS 



dilute it, and then get material for fresh blood preparations and films 

 without undue squeezing, which is to be avoided. Of course, fresh 

 punctures can be made. Ordinarily, complete blood examinations are 

 not called for. It is only a white count or a differential count or 

 an examination for malaria that is required. 



As a practical point it is very rare that a red count is indicated. There is one 

 point not sufficiently recognized by physicians and that is that a routine blood 

 examination is not apt to be as carefully conducted as one calling for a specific fea- 

 ture. Without disparaging the necessity of routine examinations of urine as well 

 as blood it is a fact that the internist who knows what he wants gets better results 

 from the laboratory man. 



HEMOGLOBIN ESTIMATION 



The most accurate instrument for this purpose is the Miescher 

 modification of the v. Fleischl haemoglobinometer. 



The magenta-stained glass wedge for comparison with the diluted blood is similar 

 in each instrument, but by the use of a diluting pipette accurate dilutions are possible 

 in the Miescher. There are two cells provided one 12 mm. high, the other 15 mm. 

 the idea of this being to enable one to make separate comparisons and to select 

 the central part of the glass-wedge scale, where comparison is more accurate than 

 at the ends. As these cells contain columns of diluted blood proportionately as 5 

 to 4, we should have similar readings when we multiply the reading on the scale 

 with the 15 mm. cell by . 



The mixing pipette is graduated with the marks J^, %j and K the first giving a 

 dilution of i to 400 (when the diluent, a 0.1% soda solution, is drawn up to the mark 

 above the bulb) the second of i to 300 and the last of i to 200. 



Artificial light preferably from a candle is necessary. There is a table accom- 

 panying each instrument which shows the value for that particular instrument in 

 milligrams per liter of haemoglobin for any reading obtained on the scale. The nor- 

 mal amount of haemoglobin in the blood is usually given as 13 to 14 grams per looc.c. 

 blood. For the first two weeks after birth the amount is much higher, 16 to 20 grams 

 per 100 c.c. After this time it begins to drop so that a child from five or six 

 months to twelve or fifteen years old only has about n grams in 100 c.c. blood. 



Sahli found variations in normal individuals of from 13.7 grams to 17.3 grams per 

 100 c.c. of blood. 



The apparatus is expensive, requires considerable time and care in the making of 

 estimations, and is exclusively an instrument for a well-equipped laboratory. 



Sahli's Haemometer. A simple and apparently very scientific 

 instrument which has been recently introduced is the Sahli modifica- 

 tion of the Gower haemoglobinometer. Instead of the tinted glass, or 

 gelatin colored with picrocarmine to resemble a definite blood dilution, 

 Sahli uses as a standard the same coloring matter as is present in the 



