( 412 ) 



Let lis now consider the case ^vlle^, in Vs li(re-flask with 100 clVP. 

 of fluid and a free surface of 80 cM^ after a month's cnltnre a 

 quantity of 20 mgrs. of dry bacterial sul)stance is formed, which, 

 calculated as cellulose, contains 44 7o C. ; we then find in the 20 mgrs. 

 of dry matter 8.8 mgrs. of carbon. According to Henriet the atmos- 

 pheric carbon compound, present in a certain quantity of air, under 

 prolonged action of alkali, gives out as much carbonic acid as occurs 

 already in a free state in the same A'olume of air, that is per liti'e 

 0.3 cM\ = 0.6 mgrs., in which 0.163 mgrs. of carbon are present. 

 Thus, for 8.8 mgrs. are wanted 55 litres of air. Consequently, in the 

 course of a month these 55 litres of air must have diffused through 

 the cotton ])lug inward and outward of our ^/^ litre-flasks, in order 

 to produce tlie found (|uantity of carbon, that is 76 c]\P. hourly. 



Though this figure should not be considered a priori as impossilile, it 

 still appears to be very high, and the difficulty of accepting it increases, 

 if still the addition has to be made of a yet unknown, but apparently 

 considerable amount consumed for the bacterial respiration, Avhich, as 

 remarked above, seems necessary. We therefore think that it 

 must be admitted that the quantity of the atmospheric compound (or 

 compounds) assimilable by B. olk/ocrirbophilifs, is much larger in our 

 laboratory atmosphere, than in that of the Paris boulevard, analysed 

 by Henriet, and that we have here to clo with an extremely 

 variable factor. The circumstance, too, that ^ve have not as yet been 

 able in our greenhouse, where the air, in the common sense of the 

 word, is surely much purer than in the laboratory, to obtain a vigorous 

 growth of B. oUyocarhophilus! pleads for this view. But here we 

 could not alwa3^s keep the temperature high enough, so that we 

 consider our experiments in this direction not yet closed. Besides, we 

 should observe, that in an empty, isolated room of the laboratory, 

 the quantities of combined carbon dra^vn from the air, were as great, 

 or onl}' little less than in the laboratory itself, where the air was 

 certainly impurer. 



We are accordingly conscious that further experiments, with fresh 

 atmospheric air are wanted to decide, whether the carbon compound 

 occurs in the atmosphere in a constant or in a varying percentage. 

 Only tliereby it will be possible to ascertain the distribution of this 

 com.pound, by which, at the same time, the signification of B. oligo- 

 carbopliilus m nature \\i\\ become clearer. 



As to this signification, the question arises wiiether our microbe 

 in substrata containing sufficient mineral nutrients (N, P, K, Mg, S, 

 Fe, Mn), but being poor in organic substances, is able to build up the 

 latter in the dark from the volatile carbon compounds occurring in the 



