196 PHYSIOLOGICAL CHEMISTRY. 



under the microscope (see Figs. 57 and 115, pages 195 and 359). 

 What do you find and what is your explanation from the stand- 

 point of osmotic pressure? 



9. Agglutination. To about 5 c.c. of a dilute sodium chloride 

 solution of ricin 1 in a test-tube add about one-half cubic centimeter 

 of defibrinated blood and shake the mixture thoroughly. Allow the 

 tube to stand about 15 minutes and examine a drop of the contents 

 under the microscope. Note the " clumping " or " agglutination " 

 of the erythrocytes, and contrast this phenomena with the appear- 

 ance of normal blood as just examined in experiment 8. 



10. Diffusion of Haemoglobin. Prepare some laky blood, thus 

 liberating the haemoglobin from the erythrocytes. Test the dif- 

 fusion of the haemoglobin by preparing a dialyzer like one of the 

 models shown in Fig. i, page 25. How does haemoglobin differ 

 from other well-known crystallizable bodies? 



11. Guaiac Test. To 5 c.c. of water in a test-tube add two 

 drops of blood. By means of a pipette drop an alcoholic solution 

 of guaiac (strength about i :6o) 2 into the resulting mixture until 

 a turbidity is observed and add old turpentine or hydrogen perox- 

 ide, drop by drop, until a blue color is obtained. Do any other sub- 

 stances respond in a similar manner to this test? Is a positive 

 guaiac test a sure indication of the presence of blood? 



12. Schumm's Modification of the Guaiac Test. To about 

 5 c.c. of the solution under examination 3 in a test-tube add about 

 ten drops of freshly prepared alcoholic solution of guaiac. Agitate 

 the tube gently, add about 20 drops of old turpentine, subject the 

 tube to a thorough shaking and permit it to stand for about 2-3 

 minutes. A blue color indicates the presence of blood in the solu- 

 tion under examination. In case there is insufficient blood to yield 

 a blue color under these conditions, a few c.c. of alcohol should be 

 added and the tube gently shaken, whereupon a blue coloration 

 will appear in the upper alcohol-turpentine layer. 



A control test should always be made, using water in place of the 

 solution under examination. In the detection of very minute traces 

 of blood only 3-5 drops of the guaiac solution should be employed. 



13. Adler's Benzidine Reaction. This is one of the most deli- 

 cate of the reactions for the detection of blood. Different benzi- 



1 A protein constituent of the castor bean. 



2 Buckmaster advises the use of an alcoholic solution of guaiaconic acid instead 

 of an alcoholic solution of guaiac resin. 



3 Alkaline solutions should be made slightly acid with acetic acid, as the blue 

 end-reaction is very sensitive to alkali. 



