132 BACTERIOLOGY OF WATER, AIR, MILK, ETC. 



to take up in a small quantity of water all the bacteria held back by the filter. Then 

 plate out on lactose litmus agar and examine colonies which do not show any pink 

 coloration. The dysentery bacillus has about the same cultural characteristics as 

 the typhoid one, so that it is important to note motility. If from such a colony 

 you obtain an organism giving the cultural characteristics of B. typhosus, carry out 

 agglutination and preferably bacteriolytic tests as well. Some strains of typhoid, 

 especially when recently isolated from the body, do not show agglutination. 



The Conradi Drigalski, the malachite-green, and various caffeine containing 

 plating media have been highly recommended. 



Isolation of the Cholera Spirillum from Water. 



The method proposed by Koch in 1893 does not seem to have been improved 

 upon by later investigators. To 100 c.c. of the suspected water add i% of peptone 

 and i% of salt. Incubate at 38 C., and at intervals of eight, twelve, and eighteen 

 hours examine microscopically loopfuls taken from the surface of the liquid in the 

 flask. So soon as comma-shape organisms are observed, plate out on agar. The 

 colonies showing morphologically characteristic organisms should be tested as to 

 agglutination and bacteriolysis. Inasmuch as the true cholera spirillum shows a 

 marked cholera-red reaction it is well to inoculate a tube of peptone solution from 

 such a colony and add a drop of concentrated sulphuric acid after incubating for 

 eighteen hours. The rose-pink coloration is given by the cholera spirillum with the 

 acid alone the nitroso factor in the reaction being produced by the organism. 



BACTERIOLOGICAL EXAMINATION OF MILK. 



A bacterial milk count is of comparatively little value as showing 

 whether a milk is dangerous or not. As a matter of fact, a milk which 

 contains several million of bacteria per c.c. might be less dangerous 

 than one containing only a few thousand, especially if in the latter 

 there were numerous liquefiers and gas producers present. There is, 

 however, one point of importance in connection with the quantitative 

 estimation of bacteria in milk, and that is the fact that in order to keep 

 the development of the bacteria within the limits of 10,000 to 50,000 

 per c.c., it is necessary that the requirements of cleanliness in milking 

 and the rapid cooling of the milk after obtaining it and the keeping of 

 the temperature below 50 C. be rigidly observed. If a milk has a 

 high count it shows some error in the handling of the milk. Anderson 

 has found that top milk contains from ten to five hundred times as many 

 bacteria as bottom milk. Centrifugally raised cream contains more 

 bacteria than that forming by gravity. In making a quantitative bac- 

 teriological examination, the principle is the same as with water. 



