( 524 ) 
On neutral meat-gelatine growth is seldom obtained ; if, however 
ammoniumearbonate or 1°/, to 2°/, ureum is added, there arise 
small coli-like colonies, surrounded by a wreath of caleiumphosphate 
crystals. 
The gelatine is not melted, but after a month, it is viscous. 
2 °/, ureum in bouillon are split in 24 hours. Of 10°/, ureum in 
bouillon 6—7 °/, are changed into ammoniumearbonate. 
In culture-media containing the necessary anorganic salts together 
with ureum, a good growth is obtained with the following compounds 
after infection : pepton, asparagine, glucose, cane-sugar, maltose, citrates, 
lactates, tartrates, and salts of volatile fatty acids (except salts of 
formic acid). 
§ 4. Lrsating cultureplates. 
The faculty in bacteria of splitting ureum ean according to the 
method of BrErinck by means of the yeast-water-gelatineplate 
2 or 3°/, ureum, be proved in a very elegant way by the Jris- 
phenomenon formed on this culture-medium by those bacteria. 
It is supposed that the ammoniumearbonate getting free at the 
decomposition of ureum causes the phenomenon, in consequence of 
the precipitation of calciumearbonate and -phosphate. 
An explication of the origin of the irisphenomenon on the yeast- 
water-ureum-gelatineplate, has, however, its difficulties, the culture- 
plate being so complicated that it is not easy to get an exact idea 
of the process. 
In the experiments with ureumbacteria on plates composed of 
water, 0.5 °/, calcium salt of an organic acid, 1°/, ureum, 0.05 °/, 
K,HPO,, 10°/, gelatine or, 1.5°/, agar, the iris-phenomenon often 
produced itself. 
The possibility of composing a simple culture-plate, if possible 
coagulated by agar, which produces the iris-phenomenon in a beautiful 
way, seemed not to be excluded, when the above facts were taken 
into consideration. 
In this way corresponding phenomena on the yeast-water-ureum-gela- 
tineplate and the irisating of more complicated culture-plates might 
be generally explained. 
After some trials I succeeded in the following manner in composing 
a plate which entirely answers the requirements. 
In pure water agar + 0,5°/, calciummalate or -lactate and 0,05 °/, 
ammoniumcitrate are dissolved; the melted agar is cooled down 
to the still just liquid state, after which a K,HPO, solution is 
