258 FERMENTS AND ANTIFERMENTS 



6. The tissues are again gone over with a sterile forceps, and a search 

 made for brown masses resembling blood-clots. These are to be dis- 

 carded. 



7. The tissue is now preserved in a sterile jar containing sufficient 

 sterile water and chloroform and covered with toluol. All tissue should 

 be handled with sterile forceps, and when once removed from the jar, 

 they should never be returned. The whole operation requires several 

 hours and it should be conducted without interruption. If the process 

 is interrupted, the tissue should be covered with a layer of toluol. 



8. It is well to try out the tissue with a known serum of pregnancy 

 to make certain that it is a suitable substratum. 



9. Only normal placenta should be used, as in certain instances a 

 normal organ may be satisfactory, whereas a diseased organ would be 

 unsuitable. 



10. Animal placenta may be substituted for human placenta and 

 vice versa, but Abderhalden cautions against this substitution until 

 further work has been done. 



The Blood-serum. The serum to be tested must fulfil three condi- 

 tions: 



(1) It must contain the smallest amount of dialyzable substances 

 that would react with ninhydrin. Blood is best drawn in the morning 

 before breakfast. In all diseases accompanied by marked protein dis- 

 integration, such as cancer, the blood-serum may contain large amounts 

 of dialyzable substances. 



(2) It must be absolutely free from hemoglobin and clear. 



(3) It must be free from cells. Even an apparently clear serum may 

 contain millions of erythrocytes. 



1. From 10 to 20 c.c. of blood are withdrawn from a vein at the 

 elbow with a dry sterile needle into a sterile centrifuge tube. This is 

 placed aside at room temperature for several hours, when sufficient 

 serum has usually separated out; if this has not occurred, centrifuge for 

 several minutes. The serum is removed to a second sterile centrifuge 

 tube, and centrifuged at high speed for several minutes until all cor- 

 puscles have been precipitated to the bottom of the tube. 



2. The serum should be used within twelve hours after the blood has 

 been withdrawn. Abderhalden claims that heating a serum to 60 C. 

 robs it of its digesting powers. Pearce and Williams have found that 

 inactivation considerably weakens the reaction, but does not abolish it 

 altogether. 



3. Specimens of blood sent through the mails are really unsatisfac- 



