88 A TEXTBOOK OF PHYSIOLOGY 



to the mark 101, and the mixture well shaken. For diluting normal 

 saline 3 per cent, sodium chloride, or Hayem's solution,* may be used. 

 For counting both forms of corpuscles, Sherrington's or Toison'sf 

 fluid may be employed. These contain a dye (methylene blue or 

 methyl violet) which stains the pale cells and enables them to be counted 

 more readily. 



After a thorough shaking the first few drops of fluid are rejected, 

 and then a drop of the mixture is placed upon the platform and mounted 

 with a cover -glass. Any excess of fluid runs into the surrounding 

 well. Care is taken that there is not sufficient fluid to fill the well, 

 otherwise the film beneath the cover -glass is altered in thickness and 

 the result vitiated. The scale on the platform is focussed, and the 

 cells in a square -and those lying on two of its adjoining sides are 

 counted. Usually 40 to 100 squares are counted. Each, square is 

 -^^ of a square millimetre in area, and the depth of the cell is 0-1 milli- 

 metre. Over each square, therefore, lies j^^ cubic millimetre of the 

 diluted blood. On multiplying by 4,000 the average number of cor- 

 puscles found in each square, and again by 100, because of the dilution, 

 the number in 1 cubic millimetre of undiluted blood is obtained. For 

 example, 12x4,000x100=4,800,000, about the average number in 

 man's blood. 



The Origin of the Red Corpuscle. The origin of the red corpuscle 

 varies with the stage of existence. 



1. In early foetal life the nucleated red corpuscles are first formed 

 from the mesoderm where- ever the formation of capillary vessels ia 

 taking place (Fig. 20). 



,erythrocyte. 



T-. . -A**" W\ X KK W'" Lr-ST " KJi-i^X' 



mesoblast- 



uasoform. cell 

 hypoblast- 



FIG. 20. SECTION ACROSS YOLK SAC SHOWING BLOODVESSELS AN:> NUCLEATED Ri:n 

 BLOOD -CORPUSCLES FORMING IN ITS MESOBLASTIC LAYER. (Keith, after Selenka.) 



The cells (angioblasts) in the region where a capillary is to be- 

 formed unite together to form a syncytium (a fusion of cells). Their 

 nuclei divide at some places faster than others, so that an accumula- 

 tion of colourless cells (primitive hajmoblasts) is formed at certain 

 points. These cells become coloured by the formation of haemoglobin 

 within them, and form the primitive coloured cells of the blood the 

 so-called primitive erythroblasts. A hollowing-out process now takes 

 place at the enlargements, and the newly formed corpuscles float in 

 a clear fluid in the cavities thus made, the whole forming so-called 



* Hayem's solution consists of: Mercuric chloride, 0-5 gramme; sodium sulphate, 

 5 grammes; sodium chloride, 1 gramme; distilled water, 200 c.c. 



t Toison's solution is: Methyl violet, 0-025 gramme; sodium chloride, 1 gramme;, 

 sodium sulphate, 8 grammes; glycerine, 30 c.c. ; distilled water, 160 c.c. 



Sherrington's fluid is: Methylene blue, 0-1 gramme; sodium chloride, 1-2 grammes;, 

 neutral potassium oxalate. 1-2 grammes; distilled water, 300 c.c. 



