234 MILK HYGIENE 



diluted through, the gelatin tubes. Agar-agar is pre- 

 ferred to gelatin because it can be used for plates to be 

 incubated. If comparative counts are to be made the 

 apparatus and temperatures of incubation and the char- 

 acter of culture media should be the same. Porous 

 Petri dish covers are preferred to glass covers because 

 they tend to prevent spreading colonies. For a descrip- 

 tion of the method used in the bacteriological examina- 

 tion of milk in the laboratory of the Boston Board of 

 Health see a paper by Slack in the Journal of Infectious 

 Diseases, Supplement No. 2, February, 1906. L. P.] 



The detection of specific pathogenic bacteria is so 

 difficult and the examination gives such unreliable re- 

 sults that practically it is not worth while to search for 

 them. The bacteria of typhoid fever and diphtheria have 

 rarely been discovered through the use of cultural meth- 

 ods; the tubercle bacillus may sometimes be discovered 

 under the microscope but usually it is present in such 

 small amounts that it cannot be detected. The best way 

 to examine milk for tubercle bacilli is by inoculation of 

 experimental animals. A conclusion, however, cannot 

 be drawn from this experiment until one or two months 

 have elapsed. 



e. [Examination for cells. The examination of milk 

 for pus was first suggested by Dr. Stokes of Baltimore, 

 and has since been carried out in a number of public 

 health laboratories in different parts of the United 

 States. The researches of Stokes, Bergey, Stewart, 

 Doane, Slack, and others have shown that cells are pres- 

 ent in practically all samples of milk and that in some 

 samples the cellular content is much higher than is usual. 

 Where the number of cells is high it is customary to 

 regard them as pus cells, but there is no general agree- 

 ment as to where the line should be drawn. The question 

 is a difficult one because pus cells and dead leucocytes 



