1147 
condensed around the colonies and forming an iridescent layer on 
the agar. 
On comparison of the velocity of growth of the various species, 
much difference between them is observed. 
By direct sprinkling of soil, canal water, or other material on 
the plates, several species which do not accumulate in the deseribed 
culture liquids, can be isolated. Moreover it is possible in this way 
to determine the number of paraffin-oxidising microbes in any ma- 
terial. So, in one gram of garden soil at Delft + 50,000, in one 
em”. canalwater == 8000 paraffin-oxidising microbes were found, 
which shows that they are very common. 
It is clear that this method is also applicable to other volatile 
compounds. 
For a nearer examination the cultures were sown, beside on the 
above plates, on broth gelatin and broth agar, and on media of 
other composition. 
Accumulation of parafjin-oxidising species at various temperatures. 
When the above media, consisting of tapwater, anorganic salts, 
and one of the hydro-carbons, are placed at temperatures between 
15° and 25° C. and the transfers are also cultivated at these tem- 
peratures, B. fluorescens liquefaciens, B. punctatus, and other lique- 
fying species are particularly obvious, but there likewise occur some 
fat splitting, non-liquefying bacteria and micrococci, oe can all 
be distinguished on broth gelatin. 
In the tubes placed at 26°—80° C. the number of liquefying 
bacteria is still very great, yet, non-liquefying species are more com- 
mon than at lower temperatures. At the same time the non-fat- 
splitting group of the paraffin-oxidising species, the mycobacteria, 
begin to develop, but especially at 30°-—37° C. they find their 
optimum. They are very striking by their morphological properties 
and pigment formation. 
By this method white, brown, red, and red-brown species were 
Isolated. At 37° C., with paraffin as carbon source, a fat-splitting 
micrococcus developed in almost pure state, which oxidised paraffins 
vigorously ; it was called Micrococcus para ffinae and is in its properties, 
except in shape, similar to B. kpolyticum *). 
If instead of garden soil, sewage water is used for the infection, 
the growth of fluorescents and of B. pyocyaneus may become so intense, 
1) These Proceedings, 1911. 
