[HARRISON A leckJ .\ESCULIN BILE SALT MEDIA 109 



be easily and accurately estimated. Such a method is furnished by the 

 use of a^sculiu bile salt agar, which will permit of an accurate deter- 

 mination of the number of B. coli and B. cerogenes present, and thus 

 give information regarding the amount of filth and particularly manure 

 in the sample. One of us in a previous investigation '" has shown that 

 B. cerogenes is as frequently present in cow manure as B. coli, and also 

 that both organisms are present in large numbers on the bodies of 

 various species of flies. 



We have already pointed out that œsculin will give black colonies with 

 both B. coli and B. cerogenes, hence both organisms may be counted on 

 the plates, and on account of the différent character of their colonies 

 separate counts may be made of each. In jiractice we usually make 1 

 in 100 and 1 in 500 dilutions for ordinary milk, but this is hardly 

 sufficient for poor milk and a higher dilution may be necessary. 



At this stage of work, we can hardly suggest a standard until other 

 laboratories give the a^sculin method a trial and confirm our results, 

 but tentatively we may suggest that if the 100,000 bacteria per c.c. 

 standard is in use, the nmnber of B. coli and B. cerogenes should not 

 exceed 1,000 per c.c. or 1 per cent. 



"We are also of the opinion, as the result of a large number of analyses 

 that compared with ordinary beef peptone agar, sesculin bile salt gives a 

 better idea of the sanitary condition of milk samples and gives such results 

 in 24 hours, and if only one set of plates was made from each sample, we 

 should prefer to use sesculin bile salt agar. The class of liquefying 

 bacteria which are also able to give some indication of the sanitary con- 

 dition of stables, etc., cannot be estimated on agar plates, and this point 

 is mentioned because the milk committee of the American Public Health 

 Association have recommended agar plates in preference to gelatine, in 

 the routine examination of milk in public health laboratories. 



No experimental data are given in this paper, but the experimental 

 results on which this paper is based will be given at an early date. 



REFERENCES. 



1. Mr('o)il-nj d Hill. Thompson Yates Laboratories, Reports IV. p. 151, 



1901. 



2. Gruniaum d Hume. British Medical Journal, 1902, p. 1473. 



3. Winslotc d- Hunnewdl. Journal of Medical Research, VIII., p. 502. 



Whipple. Technology Quarterly XVI., p. 18. 



Fuller d Fcrguaon. Journal of Infectious Diseases, Supplement 1, 1905. 

 p. 142. 



