108 ;royal society of canada 



sent per c.c, in the small quantities of water used in pouring the plates. 

 The method usuall}^ employed is as follows: We add 1 and 5 c.c. of 

 water to two test tubes of œsculin bile salt broth, and place in sterilized 

 Petri-dishes, one, two, three, or five c.c. of water respectively. After 

 using sufficient of the sample for other plates, 10 c.c. of four timc-s 

 strength œsculin bile salt ijroth is added to the sample bottle, and all 

 rubes, plates, etc., are incubated at 37.5" — 40°C. 



We have found that just as good results may be obtained from aesculin 

 bile salt agar, as from a-sculin bile salt broth in fermentation tul)es, and 

 the agar offers the further advantage tluit any black colonies may be sub- 

 cultured in 24 hours, whereas if a positive reaction takes place when 

 using œsculin broth, plates must be made before B. coli can be isolated 

 in pure culture. Our experience also shows that the black coli-like 

 colony on aesculin agar is a '' presumptive " test of greater merit than 

 red colonies in the neutral red bile salt lactose agar or gas and acid in 

 dextrose broth. The disadvantage is the comparatively small amount 

 of water that can be used. Larger plates and larger fermentation tubes 

 allow 10 c.c. samples to be taken. 



Our sample bottles hold about 200 c.c. of water and with the addition 

 of aesculin bile salt broth four times strensth serves as an enrichment 

 medium, inhibits the growth of forms other than B. coli and B. aerogcnes, 

 and at the same time furnishes an indicator or presumptive test for 

 B. coli. We have found that this presumptive test is correct in more 

 than 90 per cent of our samples, or in other words, more than 90 out of 

 every 100 samples which give a positive reaction in aesculin broth eon- 

 tain " excrétai B. coli, " adopting tlie definition of Savage^ or are 

 " flaginac, " using the basis of classification suggested by Houston. 



Aesculin Bile Salt Media for Milk Analysis. 



The routine bacteriological examination of milk in liealtb labora- 

 tories usually consists of plating samples in beef peptone gelatine and 

 beef peptone agar, at 20° C, and 37° C, respectively. The plates are 

 counted and the total number of bacteria computed per cubic centimetre 

 of the sample. The species of bacteria present are seldom noted, owing 

 to the large amount of work involvod in sub-culturing the various 

 colonies. 



The total number of bacteria found in any given sample of milk may 

 or may nt>t give indications of dirty cows and unsanitary utensils and 

 stables, for the milk may have come from clean animals and sanitary 

 stables, but may have been kept in a wann place which would give a 

 high count. Hence the advisability of introducing a simple method of 

 analysis, whereby the bacteria associated with dirt, manure, etc., may 



