( 401 ) 



of P>. uliiiociirfxnihiliis, (if w liicli more Ix^low, a .u"!)!»! (Irxclopmciil of 

 llic liliii is possible, liv which cxpcriiiiciil il can al Ihc same 

 time l)(' jH'ox'cd, Ihal this mici'ohc ilscll' (h>cs no! iiilril'v. llciicc, 

 aiuinoiiiiiiii salts or nitrites, added to excess can, excii I'oi- a 

 vear or lon<i;er. coiiliiiiie iiiichaii.u'ed under the Inxnrianllv urow iiiii,- 

 |>cllicle of />. (>ri(i(>ciirl)(ii)liilns, \\ hereas, in the |>rcseiK'e of nitril\ iiii:- 

 rcrniciits. Ihev coni|>leIelv disa|t|)ear in a few weeks, heinu' then 

 foujid hack as iiiti'ales. If liie fernieiils of nilrilicatioii alone are 

 jH'eseiit, IIkm'c is jio «pieslion of lilni-foi-inatioii and the nntrient 

 solutions i-eiiuii)i ]»erfec(lv clear. 



Not oidy the nalni'c of the iiitro,ii:en-fni-nishin,ii- sid>stances, l)nt also 

 theii' <|nanlity can in these expei'iiiieiits, as already inferred in the 

 I'ecipes, \ar\" hetwecMi fairly wide linnls, and the saiiK^ may I*e said 

 concei'iiiuii' Ih** conditions for the \\aler cidlure of hiuhei- and lowci' 

 ureeu j)lanls. 'i'he limits allowable for i>. (>//(/oc((r/jo/)/i/7ns, tunc 

 not yet heen precisely fixed, hut they cerlaiidy have a hroader rauL^' 

 foi' this oriiaiiisiu (circa O.J — 10 pro mill(^) than for the higher 

 plants (0.5 — 5 |»ro mille). 



IJy many ex[)erimeuls it was established, that in absence of kalium, 

 |)liosphor. and ma,uiiesium, a still sliüliler jii-owth occurs, than when 

 no nitroueu compounds are Lii\'en. Ex'idenlly />. (>//</oc(trfHi/>////Hs finds 

 in the almos|)here, in a condition lit for nutrition, a (piantily (»!' 

 nitrou'en, which, aHhou^h insufiicient, should not be o\-erlooke<i. 



if the distilled water in the artificial solution is replaced by lap-water, 

 a somewhat hi<ilier rate of öi;uanic substance is pi-oduced. As in tap- 

 \\atei- a small (piantity of nitroii-en compounds occui*. — here, at 

 Delft, about 0.4 milli.ui-ams of combined nili-ou'cn per litre. — 

 whilst il coidains the other iiecessary elements (phosjdior and kalium, 

 of course, exce|)ted) in an obviously favoi-able foi-m foi' the nutrition 

 of onr mikrobe, one can sim[)ly use foi' ils culture: 



Tap-watei- J 00 



Dikaliumpliosphatc 0,02. 



It should, however, be ke])t in view, that the productivity in bac- 

 tei'ial substaiu'c, in conseipieiu-e of the lilm formation, is not deler- 

 inijied by the volume, but chiefly by the extent of tlie surface of 

 the metlium, which is in free coiitact w itli the air. Hence, in a very 

 thin layer of iai^water, the nitrogen may soon be consumed, whereas, 

 witi: ti^e same amount of nutrient li(pu(l, but with a smaller surface, 

 ('01 ^eipiently in a thicker layer, the [)i-(nision of nih'ogen will suHice 

 for a longer time. Therefore, in ordei- to obtain from a flask of 

 determined size, llie niaximum production of ./). ol 'kj oca rboph 'this, a 



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