PRECIPITINS 921 



serum. Prepare 1:100 dilutions with normal salt solution; set up the following in 

 long narrow test-tubes: 



Tube 1: 2 c.c. of normal horse serum (1:100) +0.1 c.c. antihorse serum. 

 Tube 2: 2 c.c. of normal horse serum (1: 100) +0.1 c.c. antihuman serum. 

 Tube 3: 2 c.c. of normal human serum (1:100) +0.1 c.c. antihuman serum. 

 Tube 4: 2 c.c. of normal human serum (1:100) +0.1 c.c. antihorse serum. 

 Tube 5: 2 c.c. of normal guinea-pig serum (1:100) +0.1 c.c. antihorse serum. 

 Tube 6: 2 c.c. of normal guinea-pig serum (1: 100) +0.1 c.c. antihuman serum. 

 Tube 7: 2 c.c. of normal salt solution+0.1 c.c. antihorse serum (control). 

 Tube 8: 2 c.c. of normal salt solution+0.1 c.c. antihuman serum (control). 



3. Do not shake the tubes; place them in the incubator at 37 C.; inspect every 

 thirty minutes for two hours. 



(a) Discuss the question of specificity of precipitins. 



(b) Of what practical value are precipitin reactions? 



(c) Enumerate the chief points in the technic of a precipitin reac- 

 tion in the differentiation of proteins. 



EXERCISE 25. PRECIPITINS (Continued) 

 EXPERIMENT 65. FORENSIC BLOOD TEST 



1. Secure from the instructor two pieces of muslin or gauze containing respec- 

 tively a stain of human and horse blood. These are to be numbered and the source of 

 each stain known only to the instructor. Secure 1 c.c. each of normal human and 

 horse serum and dilute 1 : 1000. 



2. Prepare extracts of each stain as described in the text (Chapter XVII). 



3. Secure 1 c.c. of clear antihuman and antihorse immune serum. 



4. Set up the following in long narrow test-tubes: 



Tube 1 : 2 c.c. of extract No. 1 in dilution of 1 : 1000+0.1 c.c. of antihuman serum. 



Tube 2: 2 c.c. of extract No. 1 in dilution of 1 : 1000+0.1 c.c. of antihorse serum. 



Tube 3: 2 c.c. of extract No. 2 in dilution of 1: 1000+0.1 c.c. of antihorse serum. 



Tube 4: 2 c.c. of extract No. 2 in dilution of 1 : 1000+0.1 c.c. of antihuman serum. 



Tube 5: 2 c.c. of normal human serum in dilution 1:1000+0.1 c.c. antihuman 

 serum (control). 



Tube 6: 2 c.c. of normal horse serum in dilution of 1:1000+0.1 c.c. antihorse 

 serum (control). 



Tube 7: 2 c.c. of normal salt solution+0.1 c.c. of antihuman serum. 



Tube 8: 1 c.c. of normal salt solution+0.1 c.c. of antihorse serum. 



5. Do not shake tubes; place in the incubator at 37 C. and inspect every thirty 

 minutes for two hours and after standing in the refrigerator overnight. 



(a) Inspect the controls. Are the antiserums potent and satis- 

 factory? Why is it advisable to have these controls? 



(b) Are you able to diagnose the source of each stain? 



(c) In a medicolegal test, if these reactions were negative, how would 

 you proceed further in your efforts to establish the identity of a particu- 

 lar stain? 



