THE PRECIPITIN REACTION. 



8 9 



legal work where the greatest possible specificity is desired the 

 earlier reading is better, whereas in the study of relationships a 

 later reading is preferable. Experience has shown that one 

 hour is the latest time at which the ring test may be read satis- 

 factorily at room temperature. After that time the rings become 

 diffuse and tend to disappear. 



5. The Effect of P H on the Titer of an Antiserum. 



An antibeef serum (A8) was titrated at several different P H 

 values as shown in Table V. The buffered solutions were made 

 according to Sorenson's tables as recommended by Evans (1922) 

 and were tested colorimetrically after sterilization in the auto- 

 clave. The homologous readings at one hour are given in the 

 table. 



TABLE V. 



THE EFFECT OF PH ON TITER. 



From the data given in Table V. it may be seen that a spon- 

 taneous precipitate often appeared in the controls below a PH 

 of 7. The titer of the antiserum was not affected in any marked 

 way except through the effect on the control. Such a spon- 

 taneous precipitate in the control must be prevented and this 

 alone justifies the use of buffered solutions in the precipitin test. 

 Other workers claim even greater effects of the P H on serological 

 reactions. 



6. The Effect of Sodium Chloride Content on Titer. 



The titrations of rabbit antisera have all been made with 

 .85 per cent, buffered saline with a PH of 7 except in special 



