216; 



BACTERIAL VACCINES 



ployed for the enumeration of blood-corpuscles, the diluting and staining 

 fluid being made by adding to a 1 per cent, solution of sodium chlorid 

 in distilled water sufficient formalin to make 2 per cent., and alcoholic 

 gentian-violet, 5 per cent. The emulsion is drawn up in a white cor- 

 puscle pipet to the mark 0.5, and with diluting fluid to the mark 11. 

 The contents are then mixed thoroughly for several minutes, several 

 drops expelled, a drop placed in the counting chamber and properly 

 covered with a special thin cover-glass. The bacteria are allowed to 



remain in the counting cell for 

 at least half an hour prior to 

 enumeration. A large number 

 of small squares are counted, 

 and the average of one square 

 obtained. By multiplying this 

 figure by 4000 and then by 20, 

 the number of bacteria per 

 cubic millimeter is obtained, 

 and 1000 times this figure 

 gives the number of bacteria 

 contained in one cubic centi- 

 meter of the vaccine. If the 

 emulsion is highly concen- 

 trated, the red cell pipet may 



be used and the calculations 

 made accordingly. 



(c) Method of Kolle.A 

 platform loop adjusted to fit 

 No. 2 of a Lautenschlager wire 



FIG. 62. INSTRUMENT FOB THE STANDARDIZA- 

 TION OF PLATINUM LOOPS. 



4 mm., and holds approxi- 

 mately 2 mg., or about 2,500,000,000 organisms. By growing an 

 organism on slants of agar and emulsifying a certain number of loopf uls 

 in a measured quantity of saline solution, an approximate method 

 of standardization is obtained. According to Kolle, ordinary slants of 

 agar will hold about 15 loopf uls of staphylococci, Bacillus typhosus, 

 or Bacillus coli, and about 5 loopfuls of streptococci and gonococci. 



(d) Method of Hopkins. 1 This is based upon concentrating a 

 bacterial suspension by centrif ugalization and the preparation of stand- 

 ard emulsions from the sediment. The emulsion is filtered through a 

 i Jour. Amer. Med. Assoc., 1913, xl, 1615. 



