BACTERIOLOGICAL TECHNIC. 63 



b. Every sample should be thoroughly mixed before making cultures. 

 Shake well, about twenty times. This is very important. 



c. All glassware, pipettes, etc., must be thoroughly sterilized by washing, 

 use of disinfectants, rinsing, wiping, hot air and steam sterilization, etc. 



d. Incubate at room temperature, as a rule. Colonies- will begin to 

 appear in forty-eight hours. The maximum development will be in three or 

 four days, in most instances, provided the temperature does not fall below 

 20° C. 



e. As a rule the presence of abundant gelatin-liquefying organisms 

 may be looked upon with suspicion. Certain sewage organisms liquefy 

 gelatin very actively. 



f. The colon bacillus and some sewage cocci give pink colonies with 

 lactose litmus agar medium. The cocci colonies are a deeper vermilion 

 than the colon colonies. Sewage-contaminated water will show many pink 

 colonies. 



g. Certified milk (just delivered) should not show more than from 1000 

 to 10,000 colonies per c.c. 



h. Wholesome uncertified milk should not show more than from 30,000 

 to 50,000 colonies per c.c. The number of colonies permissible varies in 

 different states and in different localities in the same state. The number of 

 colonies may range from 25,000 to 1,000,000 per c.c, and even more, and yet 

 the milk may be pronounced wholesome. No pink colonies should be present. 

 No pus cells should be present (centrifugalized sediment). 



i. Good drinking water should not show more than 50 to 100 colonies 

 per c.c. and there should be no pink colonies, only a few liquefying colonies 

 (i-io) and most of the colonies should develop best at '20° C. If 50 per 

 cent, of the colonies develop best at 30° to 38° C. this indicates probable 

 sewage contamination or contamination with intestinal bacteria. This 

 differential temperature test is considered of importance in the bacterial 

 examination of drinking waters. Norinal water gives a proportion of i 

 colony of high temperature organisms to from 25 to 50 colonies of low 

 temperature organisms. In sewage contaminated water the proportion is i 

 to 4 and even less. 



j. Thus far there are no standards for the bacteriological testing of phar- 

 maceuticals. Tinctures and fluidextracts should show only few colonies per 

 c.c, not over 30 to 60. Sera should show none. Well prepared and prop- 

 erly ripened small-pox vaccine should show only a few colonies per point or 

 per glycerinated tube. Aquas often show abundant colonies, from 10,000 

 to 10,000,000 per c.c. and more. 



k. The colon bacillus should not be present in drinking water, in milk 

 or in pharmaceuticals. If present, it indicates sewage or other objectionable 

 contamination. The colon bacillus is motile in young broth cultures, forms 



