1*5 



4. T h e nutrition with atmospheric carbon. 



A good appreciation of the carbon accumulation may be had as well by a direct 

 weighing as by the permanganate method. 



For both determinations it is possible, to suck oft" the fluid, which is practically 

 free from hacteria, wholly or partly from beneath the film, so that the quantity of the 

 culture material, destined for the nitration or the determination of the permanganate 

 number, is not too voluminous. 



In our experiments there only resulted a precipitate of calciumphosphate or cal- 

 ciumcarbonate, when we had used our tap-water, which is rich in lime, and when 

 kaliumphosphate, to excess had been added. These precipitates can, however, be dissol- 

 ved beneath as well as in the film by dilute acid, and then the acid can be expelled by 

 further washing. The film is so dry and wetted with so much difficulty, that all these 

 manipulations may be effected without much loss of material. 



The permanganate number was determined after K u b e 1's *) method. 



In relation to the quantity of organic matter found by direct weighing or by the 

 permanganate method and formed from the atmospheric carbon, the following should 

 be well observed. 



As B. oligocarbophilus grows only on the free surface of the medium, and not 

 in the depth, the thickness of the layer of the nutrient solution and consequently its 

 volume, is, as already observed, actually indifferent. That is to say, by enlarging the 

 surface of the solution, a bacterial film of any dimensions is to be obtained, which 

 circumstance is of importance for appreciating the productivity of a certain quantity 

 of a nutrient solution, the more so as the thickness of the bacterial film is usually 

 only one cell-layer. How very thin the required thickness of this layer can be, growth 

 being still possible, may be derived from the fact, that, especially when using distilled 

 water with nutrient salts, the film can mount at the apparently dry glass-wall from i 

 to 1.5 decimeter high, and not seldom extends on it nearly to the cotton plug. Only in 

 certain vinegar bacteria I observed the same. 



As it seems that our bacterium forms no compounds prejudicial to its growth, so 

 the only circumstance, which governs its increase relatively to a given volume of 

 liquid, provided its surface be of a sufficient extent, is the lack of one or more ele- 

 ments necessary for the nutrition. Carbon cannot be among the number, our experi- 

 ments being made with free entrance of air. 



Although it is thus established, that only the number of bacteria, produced 

 in a certain time per surface-unit, indicates the rate at which the atmospheric carbon 

 is assimilated, we will yet give the quantities in relation to the volume of the solution, 

 because then a comparison can be better made with the numbers found by other authors 

 for polluted waters. 



5. H o w much carbon is assimilated. 



First we determined by an experiment, in which, after vigorous shaking, a cul- 

 ture was divided into two equal portions, how much one half contained at direct 



') Tiemann-Gar tner's Handbuch <U-r Untersuchung der Wasser, 40 Aufl. pag. 

 255, 1895- 



