BOUILLON—GELATIN~—AGAR. 5I 
1 Substantially as recommended by the Bacteriologic 
Committee of the American Public Health Association. 
Some minor changes, suggested by Dr. H. W. Hill, in the 
Report of the Health Department of Boston for 1898, have 
been’ incorporated without detracting from their value as 
standard media. 
? Acid media are denoted by the f/us sign, and alkaline 
media by the minus sign; the degree of acidity or alka- 
linity is denoted by parts per hundred. Thus, a medium 
marked + 1.5 indicates that the medium is acid, and that 
1.5 per cent. of = sodium hydroxid is required to make it 
neutral to phenclphthalein. 
® Following is Fuller’s method of obtaining the degree of 
reaction of culture-me‘ia : 
(a) Prepare a = solution of sodium hydroxid. 
(6) Prepare a . solution of hydrochloric acid. 
(c) Transfer 5 c.c. of the medium to be tested to a porce- 
lain evaporating-dish. 
(d2) Add 45 c.c. of distilled water. 
(e) Boil for three minutes. 
(/) Add 1 cc. of a 0.5 per cent. solution of commercial 
phenolphthalein in 50 per cent. alcohol. 
(g) Titrate while still hot with the acid or alkali as re- 
quired, and determine the reaction. 
To determine exactly when the neutral point is reached, 
notice that in bright daylight the first change that can be 
seen on the addition of alkali is a very faint darkening of 
the fluid, which on the addition of more alkali becomes a 
more evident color and develops into what may be de- 
scribed as an Italian pink. A still further addition of 
alkali suddenly develops a clear and bright pink color, and 
this is the reaction always to be obtained. 
(2) When the reaction has been obtained, calculate the 
amount necessary to neutralize the bulk of the medium 
or to produce the required reaction, and add the proper 
amount of a normal solution of the acid or alkali. 
