140 PRODUCTS OF VITAL ACTIVITY. 
open for five to eight hours; the flask is then closed and kept at 18°C. It 
should be shaken every two hours. At the end of twenty-four hours the 
milk is poured through a fine sieve into another flask, which must uot be 
more than four-fifths full. This is corked and allowed to stand, being 
shaken from time to time. At the end of twenty-four hours a drink is ob- 
tained which contains but little COs or aleohol. Usually it is not drunk 
until the second day, when, upon standing, two layers are formed, the 
lower milky, translucent, and the upper containing fine flakes of casein. 
When shaken it has a cream-like consistence. On the third day it again 
becomes thin and very acid. 
‘* The second method is used when one has a good kefir of two or three 
days to start with. Three or four parts of fresh cow’s milk are added to one 
part of this and poured into flasks which are allowed to stand for forty- 
eight hours with occasional shaking. When the drink is ready for use a 
portion (one-fifth to one-third) is left in the flask as ferment fora fresh 
quantity of milk. The temperature should be maintained at about 18° C.; 
but at the commencement a higher temperature is desirable. The kérner 
should be carefully cleaned from time to time and broken up to the size of 
peas. The cleaned kérner may be dried upon blotting paper in the sun or 
in the vicinity of a stove: when dried in the air they retain their power to 
germinate for a long time.” 
Fermentation of urea. The alkaline fermentation of urine is 
effected by various microérganisms, but chiefly by the Micrococcus 
ureze, the ferment action of which has been carefully studied by Pas- 
teur, Duclaux, and others. The change which occurs under the 
action of the living ferment was determined by the chemist Dumas 
as long ago as 1830, but it remained for Pasteur to show that this 
change depends upon the presence and vital activity of a living 
microérganism. 
The transformation of urea into carbonate of ammonia is shown 
by the following formula: COH,N, + 2H,O = CO, + 2NH, + 
H,O = (NH,),CO,. 
According to Van Tieghem, Micrococcus ures continues to grow 
in a liquid containing as much as thirteen per cent of carbonate of 
ammonia. Itmay be cultivated in an artificial solution of urea, with 
the addition of some phosphates, as well as in urine. 
The Bacillus ureee of Miquel has also the power of producing the 
alkaline fermentation of urine, but it does not thrive in so strong a 
solution of carbonate of ammonia. 
A different micrococeus—Micrococcus uree liquefaciens—nas also 
been studied in Fliigge’s laboratory which possesses the same power. 
According to Musculus, a soluble ferment may be isolated from urine 
which has undergone alkaline fermentation, which changes urea into 
carbonate of ammonia. He obtained it from urine containing con- 
siderable mucus, in a case of catarrh of the bladder. But Leube has 
shown that cultures of Micrococcus ures from which the micrococ- 
cus was removed by filtration through clay do not induce alkaline 
fermentation. The soluble ferment obtained by Musculus must 
therefore be from some other source. 
