HEMOGLOBIN. 109 



A fresh alcoholic solution of guaiacum when oxidized gives 

 u blue color. Many oxidizing agents, like hydrogen peroxid and 

 oil of turpentine which has absorbed oxygen by standing for some 

 time exposed to the air, will not act on the guaiacum alone, but 

 will do so if haemoglobin or its compounds are present to serve as 

 a carrier of oxygen. This is often used as a test for blood, but is 

 only useful in a negative way, for protoplasm will give the same 

 reaction. It can consequently be obtained from any cell, like pus 

 or mucus, or even from such substances as the potato. If the 

 reaction fails, however, there can be no blood present. 



Since haemoglobin is a proteid, containing an albu- 

 minous substance, it will give the general reactions of 

 these compounds. 



The determination of the amount of haemoglobin in 

 the blood is made by comparing the color of the diluted 

 blood with a solution containing a known weight of haemo- 

 globin, or with some other colored liquid or solid. For 

 making a standard solution of haemoglobin the recrystal- 

 lized substance is used (Experiment 257). A solution of 

 this can be preserved in a corked bottle or sealed tube for 

 an indefinite time. The strength is ascertained by evapo- 

 rating to dryness a given volume, and weighing the residue 

 of haemoglobin. This method gives accurate results. 



242. DETERMINATION OF THE AMOUNT OF HEMO- 

 GLOBIN IN BLOOD. Dilute a solution* containing a known 

 weight of haemoglobin with distilled water until it is a very 

 light-red color. Dilute in the same way the blood to be 

 tested until the color is the same. For comparison of 

 colors the two solutions may be placed in flat-bottomed 

 tubes of colorless glass (Nessler tubes) or in small, flat, 

 glass boxes, the breadth of which between the parallel sides 

 is not more than a centimeter. Reckon from the amount 

 of dilution the amount of haemoglobin compared with the 

 standard solution, also the absolute weight and percentage. 



