1 88 



from i June to i Dec. we found 165.5 mgrs. of dry bacterial substance, corresponding 

 with ca. 83 mgrs. of permanganate per litre. As we see, the differences are con- 

 siderable. 



When a little natrium acetate was added to the anorganic solution, and when 

 using a pure culture for inoculation, we could neither state an augmenting nor a 

 diminishing of growth. 

 Thus we obtained in: 



Distilled water 100 



KC1 0.02 



KNO; o.i 



Natriumacetate 0.02 



K2HPCU 0.02 



Mineral solution* i drop 



by means of weighing, 220 mgrs. of dry bacterial substance per litre, corresponding 

 with no mgrs. of permanganate, which figures are not exceedingly high and might 

 likewise have been produced in the same time (4 months) from the air alone, without 

 acetate. 



In all these experiments with distilled water, the free surface of the liquid was 

 also 80 cM 2 , and the air had to pass through a dense cotton plug, with which the 

 Erlenmeye r-flasks were closed. Already before we drew attention to the impor- 

 tance of the way in which the flasks are closed; be here still mentioned that we made 

 seme special experiments, which proved that a very narrow opening of the flasks, 

 slackens the growth of B. oligocarbophilus, so that years may go by before the film 

 has vigorously developed. We could not, however, expected anything else, for the 

 considerable volume of air, required for the growth of the said quantities of bacteria, 

 can only very slowly diffuse inward and outward through the narrow canal. 



6. Carbonic acid cannot serve as food. 



Various experiments were made to establish what may be the volatile atmo- 

 spheric carbon compound which renders the growth of B. oligocarbophilus possible. 

 That it cannot be carbonic acid, whether free or combined, resulted from the follow- 

 ing experiments. In closed culture-flasks with the best nutrient solutions, and ar- 

 ranged in such a way, that at times a little free carbonic acid mixed with pure air, 

 could artificially be introduced, it was not possible to get any growth. This experi- 

 ment, which seemed of particular interest, has been so frequently repeated, and so 

 long continued under different conditions, that we consider it as quite certain, that 

 free carbonic acid cannot serve for the nutrition of B. oligocarbophilus. 



For testing the influence of combined carbonic acid, cultures were made, firstly 

 in the following solution: 



Tap-water 100 



Dikaliumphosphate o.oi 



Kaliumnitrate o.oi 



Natriumbicarbonate o.i 



\\hen cultivating at the free air surely a luxurious growth was obtained, but it 

 was by no means more vigorous than when the bicarbonate was left out. 



