210 METHODS FOR THE ANALYSIS OF BLOOD 



Preparation of the Acid Hematin Standard 



A quantity of blood (usually 50 c.c.) is obtained, carefully 

 defibrinated, and then strained through gauze. The oxygen 

 capacity of this blood is then determined by the Van Slyke method. 

 Accepting the Haldane figure of 18.5 volume per cent for the oxygen 

 capacity of normal blood (corresponding to approximately 14 gms. 

 of hemoglobin per 100 c.c.) the blood is diluted with 0.1 N HC1 

 so as to make a 20 per cent solution of a blood with an oxygen 

 capacity of 18.5 volume per cent. That is, if the blood has an 

 oxygen capacity of 18.5 volume per cent, 20 c.c. of it are diluted 

 to 100 c.c. with 0.1 N HC1; if the oxygen capacity is 22 volumes 



18 5X20 

 per cent then 16.7 c.c. ^ - of it are diluted 100 c.c. with the 



JSm 



acid. The 20 per cent solution of blood thus obtained is well 

 mixed and stored in a glass-stoppered bottle, preferably in a cool 

 spot away from the light. This constitutes the stock solution 

 from which the comparison standard is made. Such a stock 

 solution will not deteriorate for at least three months, provided 

 contamination by molds is avoided. Sahli suggests saturating 

 the acid with chloroform to keep molds from developing in the 

 solution. No other unusual precaution for the preservation of 

 this solution seems to be needed ; but before using, it should be 

 thoroughly shaken. 



The comparison standard for use in the colorimeter is made by 

 diluting 5 c.c. of the stock solution to 100 c.c. with 0.1 N HC1 to 

 make a 1 per cent standard; or 2.5 c.c. of the stock solution to 100 

 c.c. for a 0.5 per cent standard. Where routine determinations 

 are to be made, it is desirable to have the standards made fresh 

 at least once a week. 



Where determinations of the oxygen capacity of the blood are 

 not readily available, one can make the stock solution from crystal- 

 lized hemoglobin. 



METHEMOGLOBIN IN BLOOD 



Method of Stadie l 



Principle. Both hemoglobin and methemoglobin are changed 

 to cyan-hemoglobin by potassium cyanide. The total amount 

 1 Stadie: Jour. Biol. Chem., 1920, 41, 237. 



