(525 ) 
added, till a slight opalizing is observed; now the culture-plate is 
formed of this material. 
This culture-plate is, if made with care, almost clear. The calcium- 
phosphate that has been formed remains dissolved with the ammonium- 
citrate. A drop of ammoniumearbonatesolution on this medium causes 
the irisphenomenon, while after some moments produces itself a 
precipitate round the drop. 
This phenomenon shows itself in quite the same way, if, instead 
of agar, gelatine is taken. 
The irisating field and the precipitate are microscopically and 
chemically identical to those which are produced on the yeast-water- 
ureum-gelatineplate. 
If the culture-medium contains no phosphate, ammoniumearbonate 
put on it gives a very slight field of CaCO,; a drop of ammonia 
produces no irisating field at all. | 
If, however, only calciumphosphate, dissolved in ammonium- 
citrate, is present as the only calciumeompound, ammoniumearbonate 
and also ammonia on such a plate cause an extremely fine irisating 
field. 
If + 2°/, ureum is added to this plate ureum-splitting microbes 
cause thereon the “trisphenomenon’”’. 
From these experiments it appears that the calciumphosphate-preci- 
pitation has to be considered as the real cause of the irisating of the 
culture-medium, whilst the calcium-carbonate formed at the same 
time plays a subordinate part. . 
Accordingly the irisating of culture-plates by certain bacteria 
growing on them and the irzsphenomenon of BriJRRINCK have to be 
regarded as a consequence of the precipitation of calciumphosphate 
in the first and of calciumearbonate in the second place. 
§ 6. Results obtained. 
1. Decomposition of ureum, in the absence of albumen, may 
take place by different microbes, if some suitable carbon-source is 
present. 
2. In cultures in which ureum-splitting takes place, + 98°/, of 
the total energy is developed by the decomposition of the ureum. 
3. Cultures with calciumsalts of organic acids as a carbon-source, 
are extremely fit for getting weak splitting ureumbacteria. The 
bacillus erythrogenes occurring herein has been described more in detail. 
4. Cultures with ammoniumsalts of organic acids or sugars as 
