BIOLOGICAL BLOOD TEST 17 1 



are made. When, the serum is strongly precipitating the clouding of 

 the clear fluid should take place in ten to twenty minutes. 



In the biological blood lest rabbits are immunized intravenously either with whole 

 blood taken in citrated salt or with serum alone. For class work I use the blood of a 

 chicken injected intravenously into a rabbit. An immune serum thus prepared 

 contains haemolysins as well as precipitins. The haemolyzing effect of such a serum 

 on the nucleated fowl's red cells shows well when examined in a hanging drop. The 

 bleeding of the rabbit should be done after a period of fasting to avoid any opales- 

 cence of the serum. 



Precipitating sera should be kept in the cold and may have one-tenth of i % car- 

 bolic acid added as a preservative, or they may be preserved on paper strips. 



The suspected blood stain should be extracted with normal salt solution and 

 should be filtered until perfectly clear. An approximate strength of i to 1000 of the 

 blood is desirable. This can be estimated as given under albumin in urine, with the 

 U-shape tubing. 



Test: Place 2 c.c. of the i to 1000 extract of the stain to be examined in tube i, 

 2 c.c. of i to 5000 in tube 2, and 2 c.c. of ito 10,000 in tube 3, adding to each tube 

 o.i c.c. of the precipitating serum. 



In another tube put 2 c.c. of a i to 1000 salt solution dilution of the serum of the 

 animal from which the suspected blood is supposed to come and add o.i c.c. of 

 precipitating serum. 



Various other controls as with normal rabbit serum, etc., are necessary for medico- 

 legal application. 



The tubes should not be shaken and may be kept at room temperature or in the 

 incubator. A positive reaction appears in two or three minutes as a clouding at the 

 bottom of the tube which becomes a distinct precipitate in fifteen or twenty minutes. 

 Readings should be made at the end of twenty minutes as reactions occurring sub- 

 sequently have no significance. 



DEVIATION OF THE COMPLEMENT 



It has been found that if there is not sufficient immune body in a 

 mixture of normal serum, containing abundant complement, and bac- 

 terial emulsion, only a portion of the bacteria will be destroyed. In- 

 creasing the amount of immune body with a constant quantity of normal 

 serum, we reach a point where all the bacteria are destroyed. Now, 

 if we continue to increase beyond this point the addition of immune 

 serum, the destruction of the bacteria ceases, and the cultures will again 

 contain myriads of living bacteria (Neisser-Wechsberg Phenomenon). 



To carry out the test, make a series of tubes containing mixtures of bacteria with 

 the same quantity in each of normal serum. Thus, each tube contains % c.c. of 

 bacterial emulsion and ^ c.c. of i to 10 normal serum. Now inactivate a tube of 

 i to loo immune serum and to each of the tubes of normal serum and bacterial emulsion 



