BACTERIOLOGICAL TECHNIQUE. Q17 
dishes, and then soaked for from twelve to eighteen 
hours in running water; this removes excessive acidity ; 
they are then placed in test-tubes and sterilized by steam 
on two consecutive days. 
Blood-serum and Ascitic Fluid with and without the 
Addition of Bouillon. Blood-serum is used in the fluid 
state, semi-solid, and firmly coagulated. It is used 
alone, with 66 per cent. of bouillon and with 25 per 
cent. of bouillon plus 1 per cent. of glucose. Ascitic, 
pleuritic, and hydrocele fluids are also used alone, with 
bouillon, or with nutrient agar. 
The Correction of the Reaction in Media. 
Formerly it was customary to use litmus-paper as 
the indicator in neutralizing media, adding soda solu- 
tion until the mixture turned the red litmus slightly 
blue, and the blue litmus just a tinge less blue. This 
is still the best method for those who are only going 
to cultivate the common pathogenic bacteria for diag- 
nostic purposes or for the development of toxin. Most 
parasitic bacteria which grow at all on artificial culture 
media develop best in them when they have a slightly 
alkaline reaction to litmus. If a greater alkalinity is 
desired a certain number of c.c. of normal soda solu- 
tion can be added for each litre; if an acidity is desired, 
normal hydrochloric acid solution is added. 
Many bacteriologists consider that litmus is not deli- 
cate enough to be entirely satisfactory, especially when 
experiments are to be reported or exactly repeated. 
For these purposes phenolphthalein has been generally 
selected. A little experience will show that different 
indicators not only differ in delicacy, but that they 
react differently to different substances. 
