150 
per cent., is used as the nutrient medium, with 2 per cent. of 
agar, and a standard of acidity of 10 to phenol phthalein is 
allowed. Onec.c.and110c.c. of a water is taken and run into 
the melted agar, when it has cooled down to a temperature 
of 38°C. This is plated out in the usual way in a petries dish, 
incubated at 37°C for 48 hours, and all colonies that are visible 
to the naked eye are counted. These results, though they 
are extremely interesting, especially when comparing one 
sample of the same supply with that of another, cannot be 
- compared with total counts obtained on gelatine. The climate 
of this country renders gelatine as a solid medium extremely 
difficult to work with. The incubator that will maintain a 
temperature of 19° centigrade constantly, through all the 
vagaries of the Indian climate on the plains, does not appear 
to have been designed yet. Obviously, therefore, it is 
better to have a method of doing total colony counts that is 
equally satisfactory in both hot and cold weather, and, pro- 
vided that care be taken with the manufacture of the solid 
agar media, so that each batch is as nearly as possible like 
the previous one, the results obtained are valuable, and can 
be compared with each other with a reasonable expectation 
of concordance. 
In the earlier chapters the advantages and disadvantages 
of glucose and lactose in the first stages of the separation of 
feecal organism have been discussed. For all ordinary samples 
we recommend lactose, but, when it is desired to ascertain 
the preponderance of the group glucose+lactose—both media 
have to be used. 
(2) Bile salt broth.—Varying quantities of the water are 
put into these tubes. One tube receives 20 c.c. of the water ; 
2, KO C.C. 54,5: CC. ; 4, PC... 6571 Ge. 5 and'5, -0L Cee 
first three tubes a concentrated broth is used, so that the dilu- 
tion, after the addition of the water, is kept approximately 
equal). It will be observed that the first three series each 
make up to 20 c.c., so that, if there is only one tube in the first 
seven of these which gives the reaction, it means that fecal 
bacilli are present only in 60 c.c. (i.e., 3 twenties). This ar- 
rangement of obtaining a result in 60 c.c. has obvious advant- 
ages. It gives considerable information as to the number ot 
