On the Biological Examination of Water and Milk. 37 
bacilli from developing. Holtz found that about half that 
percentage (0°117) of carbolic acid in gelatine allowed the 
bacilli to develop after a few days at the temperature of the 
room (16° to 20° C.). Holtz next made a cultivating medium 
of his own—consisting of a mixture of potato-juice and 
gelatine. He took 400 grams of the juice of raw peeled 
potatoes, and 40 grams of gelatine. The potato-juice he 
allowed to stand in a cool place (under 10° C.) for twenty- 
four hours before the gelatine was added to it. This nutrient 
medium has an acid reaction which is favourable to the 
growth of the typhoid bacilli; to this medium he added 
‘05 per cent. of carbolic acid, which hinders the growth of 
moulds for six to eight days, but does not interfere much 
with the development of typhoid germs, whose growth, 
according to Holtz, is only retarded for a day. Further, the 
typhoid bacilli develop in this medium in quite a character- 
istic manner—as transparent colonies—and are thus easily 
recognised. The potato-gelatine is sterilised in the usual 
manner, and streak cultivations in test-tubes may be employed. 
If, however, the suspected water or liquid be very impure, 
then to it must be added carbolic acid in such proportion as 
to make a ‘25 per cent. solution of it. The water or liquid 
must in the next place be allowed to stand for three hours 
(at the temperature of the room), and then about 10 c.c. of 
the potato-gelatine must be seeded with } to 1 c.c. of this 
water or liquid, and cultivations made at the temperature of 
the room. It is to be noted that Holtz uses the same 
percentage (‘25 per cent.) of carbolic acid mentioned by 
Chantemesse and Widal, but he allows the organisms to 
remain in such a fluid for only three hours before transferring 
to his potato-gelatine medium. 
By the kind permission of Professor Chiene, I have been 
enabled to conduct a few experiments with the typhoid 
bacillus in his laboratory. I first made a weak solution of 
Liebig’s extract, sterilised it, and added a 5 per cent. solution 
of carbolic acid to the extract, until I had a ‘25 per cent. 
solution of carbolised extract. I then seeded it with some 
typhoid bacilli from a pure culture in gelatine, placed it in 
the incubator at 103° F., and examined drops of this extract 
