MICROCOCCUS GONORRHCEM 373 



free as possible from hemoglobin; 30 to 35 c.c. of water; 

 2 to 3 c.c. of glycerin; and finally 0.8 to 0.9 gram (i. e., 

 about 2 per cent.) of nitrose. This is boiled, with gentle 

 agitation, over a free flame, until all ingredients are dissolved 

 and the cloudy fluid has become quite clear. After such 

 boiling the mixture can be sterilized by steam without 

 precipitating the albumen, and may then be kept indefi- 

 nitely ready for use. 



When needed, the flask and its contents are heated to 

 50 C.; from six to eight tubes of 2 per cent, peptone- 

 agar-agar are dissolved by boiling, brought to 50 C., 

 and then mixed with the solution in the flask and the mass 

 poured into Petri dishes. Upon the surface of this serum- 

 nitrose-agar the cultivation is to be conducted. Wassermann 

 lays particular stress upon two points that are essential to 

 success, viz. ? the preliminary boiling of the serum-nitrose 

 mixture before steam sterilization, as this prevents precipi- 

 tation of the albumin; and the necessity of having both 

 the serum-nitrose mixture and the agar-agar, to be mixed 

 with it, at not over 50 C., for if they are at a boiling tem- 

 perature when mixed, or if they are brought to the boiling 

 temperature after mixing, the albumin will be precipitated 

 notwithstanding the presence of the nitrose,- which otherwise 

 prevents this. 



Wassermann further observes that some samples of serum 

 require to be more highly diluted with water than in the 

 proportions given above; that the agar-agar should be 

 feebly, but distinctly, alkaline to litmus, causing no red- 

 dening whatever of blue litmus paper; and, finally, that 

 the Petri dishes containing the solidified medium on which 

 the cultures are growing are best kept bottom upward, so 

 as to prevent water of condensation collecting on the surface. 



