58 A MANUAL OF PHYSIOLOGY 



alone, but the double salt sodio-magnesium sulphate precipitates 

 it, and this is formed when sodium sulphate is added to magnesium 

 sulphate.) 



(3) Dilute another portion of the filtrate from (i) with its own 

 bulk of water. Very slightly acidulate with dilute acetic acid, and 

 determine the temperature of heat coagulation. 



(4) Precipitate the serum-globulin from another portion of serum 

 by adding to it an equal volume of saturated solution of ammonium 

 sulphate. Filter. Precipitate the serum-albumin from the filtrate 

 by saturating with ammonium sulphate crystals. 



(5) Dilute serum with ten to twenty times its volume of distilled 

 water, and pass through it a stream of carbon dioxide. The serum- 

 globulin is partially precipitated. This is the starting-point of a 

 method said to be the best for obtaining pure serum-globulin. 



(6) Acidulate some serum with dilute acetic acid and boil. Filter 

 off the coagulum, and to the filtrate add silver nitrate. A non- 



FIG. 12. THOMA-ZEISS H^MOCYTOMETER. 



M, mouth-piece of tube G, by which blood is sucked into S ; E, bead for mixing ; 

 a, view of slide from above ; b, in section ; c, squares in middle of B, as seen under 

 microscope. 



protein precipitate insoluble in nitric acid but soluble in ammonia 

 indicates the presence of chlorides. 



7. Enumeration of the Blood-corpuscles. Use the Thoma-Zeiss 

 apparatus (Fig. 12). (i) Suck a drop of ox or dog's blood up into 

 the capillary tube S to the mark i. Wipe off any blood which 

 may adhere to the end of the tube. Then fill it with Hayem's 

 solution (p. 18) or 3 per cent, sodium chloride to the mark 101. 

 This represents a dilution of 100 times. Mix the blood and solution 

 thoroughly, then blow out a drop or two of the liquid to remove 

 all the solution which remains in the capillary tube. Now fill the 

 shallow cell B with the blood mixture. Put the cover-glass on, 

 taking care that it does not float on the liquid, but that the cell is 

 exactly filled. Put the slide under the microscope (say Leitz's 

 oc. III., obj. 5), and count the number of red corpuscles in not less 

 than ten to twenty squares. Sixteen squares is a good routine 

 number. The greater the number of squares counted, the nearer 

 will be the approximation to the truth. Now take the average 

 number in a square. The depth of the cell is T T Q mm., the area of 



