74 BACTERIOLO&Y. 



the reaction is determined with the ordinary red and 

 blue litmus paper. 



Soda solution is not so good as a strong solution of 

 caustic soda or potash, because the carbonic acid libe- 

 rated from the sodium carbonate is frequently seen to 

 give rise to a confusing temporary acid reaction which 

 disappears on heating. To obviate this, Schultz {Cen- 

 tralbl. f. Bdkt. u. Parasitenkunde, Bd. x., Nos. 2 and 3, 

 1891) recommends exact titration with a solution of 

 caustic soda. For this purpose a 4 per cent, solution 

 of caustic soda is prepared. From this a 0.4 per cent, 

 solution is made, and with it the titration is practised. 

 After the bouillon has been deprived of all coagulable 

 albumin and blood-coloring matter by boiling and filtra- 

 tion, and has cooled down to the temperature of the air, 

 its whole volume is exactly measured. 



From it a sample of exactly 5 or 10 c.c. is then 

 taken, and to it a few drops of one of the indicators com- 

 monly employed in analytical work is added. Schultz 

 recommends 1 drop of phenolphthalein solution (1 

 gramme phenolphthalein in 300 c.c. of alcohol) to 1 c.c. 

 of bouillon. The beaker containing the sample is 

 placed upon white paper, and the dilute caustic soda 

 solution is then allowed to drop into it, very slowly, 

 from a burette, until there appears a very delicate rose 

 color, which indicates the beginning of alkaline reaction. 

 A second sample of the bouillon is treated in the same 

 way. If the amounts of soda solution required for 

 each sample deviate but very slightly or not at all 

 the one from the other, the mean of these amounts is 

 taken as the amount of the soda solution necessary to 

 neutralize the quantity of bouillon employed. If 10 c.c. 

 of bouillon were employed, then, for the whole amount 



