FERMENT REACTIONS 327 



above, while in the actual experiments 0.2 c.c. is taken for 10 c.c. 

 of the dialyzate, each specimen being boiled for just one minute 

 (quick, uniform ebullition). If, then, no color reaction occurs in 

 any one of the tubes (see below), it has lately been recommended 

 to add another portion of ninhydrin and to boil for another minute. 

 The tubes are finally placed in a rack upon white paper and examined 

 at the expiration of half an hour. A bluish-violet color denotes a 

 positive reaction. 



Preparation of the Serum. The blood should be obtained under 

 aseptic precautions and examined as fresh as possible. From 5 to 

 10 c.c. are best withdrawn from one of the veins at the bend of the 

 elbow with a large Keidel tube, and the serum separated from the 

 corpuscles by centrifugation in the usual manner. 



While it is generally recommended to use the serum on the same 

 day on which the blood was drawn, this is not imperative and in 

 many respects it is better to procure the specimens the evening 

 before, and to let them stand overnight in the ice-box. In my 

 laboratory every specimen is centrif ugalized for fully twenty minutes, 

 the serum pipetted off, and this centrifugalized for another twenty 

 minutes. If any corpuscles are visible at the bottom the serum is 

 transferred to another tube and again centrifugalized, so as to 

 secure a specimen which is absolutely devoid of corpuscular elements. 

 If a serum presents a reddish color it should be examined with 

 the spectroscope and discarded if blood-pigment is thus demon- 

 strable. 



Finally, the serum is divided into two equal portions, the one 

 examined as such and the other after inactivation for thirty minutes 

 between 58 and 60 C. 



The Test Proper. From 0.5 to 1 gram of the placental tissue 

 together with 1 c.c. of the serum is placed in one of the diffusion 

 tubes (A) that has previously been adjusted in a small bottle con- 

 taining about 20 c.c. of distilled water, and both the serum and 

 the outer fluid covered with a layer of toluol. A second tube (B) 

 is similarly arranged, but receives serum only, and no placental 

 1 tissue, while in a third tube (C) placental tissue is placed together 

 with 20 c.c. of water, all the specimens being guarded against putre- 

 factive changes by the addition of a liberal quantity of toluol. In 

 addition to these controls it is now recommended to put up addi- 



