270 FERMENTS AND ANTIFERMENTS 



covered with toluol. From this time on they should not be handled 

 with the fingers, but only with forceps that have been sterilized by 

 boiling. Of the entire number of shells, usually from 20 to 30 per cent, 

 or more are found to be unsatisfactory. 



Preparation of the Placental Tissue. This is the substratum, and 

 should consist of coagulated placental protein free from dialyzable sub- 

 stances that react with ninhydrin. 



1. A fresh normal placenta should be prepared soon after delivery. 

 It is highly important to wash it free from all blood, Abderhalden having 

 laid considerable stress upon this point. He explains that in the blood 

 of all animals there is always a specific ferment for the red blood-cor- 

 puscles, as even the smallest hemorrhage into the tissue calls forth a 

 protective ferment. For this reason all organs that contain blood may 

 contain the substratum and ferment, and yield false positive reactions. 



2. The placenta should be placed in warm water and freed as far 

 as possible of clots. The membranes and cord are removed, and the 

 placental tissue cut into pieces about the size of a dime. These are 

 placed in a sieve under running water, and each piece squeezed with the 

 hand. From time to time the entire mass is thoroughly squeezed out 

 in a towel. Tissues that cannot be freed from clots should be discarded. 

 The tissues are now crushed in a mortar, connective-tissue strands re- 

 moved, and the washing continued until the tissue is snow white. De- 

 colorizing substances, such as H 2 02, should not be used. If the tissue is 

 not white and free from blood it should not be employed. Liver, spleen, 

 and kidney tissue cannot be made perfectly white, although all traces of 

 blood have been removed. 



3. Place 100 times as much distilled water as there is tissue in an 

 enameled vessel; to each liter add five drops of glacial acetic acid and 

 heat to boiling, when the tissue is added and boiled for ten minutes. 



4. Wash the coagulated tissue with distilled water, and boil again 

 without the addition of acid. This should be repeated six times in 

 succession. If an interruption occurs, cover the tissue and water with 

 a layer of toluol. 



5. After the sixth boiling add a small quantity of water to the tissues 

 just sufficient to enable it to boil for about five minutes without burn- 

 ing, for the water is now to be tested with the ninhydrin reaction and 

 it is important that this be as concentrated as possible. Filter the water, 

 and to 5 c.c. in a sterile test-tube add 1 c.c. of the ninhydrin solution. 

 Boil vigorously for one minute. If there is the slightest discoloration 

 within half an hour, the tissues must be boiled again, but with only five 



