LABORATORY MANUAL OF PHYSIOLOGY. 



The mast cell is not commonly found in normal blood and you 

 will probably not see it among the comparatively small number of 

 white cells that you are required to count. The cell is about twice 

 the diameter of the red cell, has a polymorphous nucleus of vague 

 outlines, and a cytoplasm containing numerous very large granules 

 taking a dark blue or blue-black stain. 



VI. ESTIMATION OP HEMOGLOBIN. 



A number of instruments have been devised for estimating the 

 haemoglobin of the blood. In most of these, for convenience of 

 comparison, a scale of 100 is used, the 100 mark corresponding to 

 a haemoglobin content of 13.8 grams of haemoglobin in 100 c.c. of 

 blood. The instruments as a rule depend on a color comparison 

 between the shed blood, with or without dilution, and a fixed scale 

 of color to correspond to various dilutions. There is a certain de- 

 gree of unavoidable error in the employment of any color test, 

 which at times may be very high. A method which avoids the er- 

 rors of the color comparisons is the estimation of the haemoglobin 

 from the specific gravity. 



The simplest, least expensive, and most practical scheme of 

 color test yet devised is that of Talqvist. 



1. Talqvist's Hsemoglobinometer. This consists of a pa- 

 per scale of color shades varying from 10 to 100 per cent haemo- 

 globin and contained in a book of filter paper which is used for 

 absorbing the specimens of blood whose percentage of haemoglobin 

 is to be estimated. The blood stain, undiluted, is compared with 

 the haemoglobin scale by reflected daylight until a shade is found 

 to correspond to the tinge of the blood examined. For approximate 

 clinical results this method is very satisfactory. 



2. Dare's Haemoglobinometer. As in the method of Tal- 

 qvist, undiluted blood is used. This is drawn by capillarity be- 

 tween two plates of glass, one of which is transparent, the other be- 

 ing translucent for diffusing the light used for illumination. 



The color comparison is made with that of a glass disc which is 

 revolved by means of a thumb screw so as to bring successive tints 



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