288 IV' CdM'KliKNCK IM KIIN \ïln\\|,i; |ii: CKM'niOI K. 



cells resembling yeasl ct'lls, iintl long sausage-sliapeci cells; llio laller nsiially 

 occur in an acid licjuid médium, and nro Uien iinilcd; Iho l'ormer occui- in a 

 siigar médium. IC liie descendants of a single round eeil are grown in an aci- 

 diiied médium (wiLiiouL sugar) a slrong colony consisting of long cells uniled 

 lo each ollier is found; il' thèse cells are grown in a sugar médium williout 

 acid, Ihe round type of cell is again formcd. 



A form orceil wliicli is prodiiced in bouillon containing i'-i |iour llKl malic 

 acid is sickle-shaped, and generally uniled. (jrown on rnusl, ur un dextrose 

 gélatine Ihey relurn lo llie normal form. 



Parallel observations hâve been made on liic lluctuations fourni in ililTcrcnl 

 micro-organisms; besides other naluralists, A»//r/j and '/.opf hâve admitleil tlie 

 variabilily of form of Ihe lower organisme, and many believe thaï a bacterium 

 may occur in the form of a coccus, and also in Ihe form of a spirillum. 



Observations on liie physiological variations of micro-organismsare of impoi-- 

 lance.' Certain organisnis cultivated successfully in an artificial metiium may 

 suddenly cease to develo[)e, and il may be thought Ihat such cultures are dead. 

 but Ihe aulhor's observations lead him lo tliink Ihal Ihis is nol oftcn the case. 

 If Ihese organisms are Iransferred to a uiedium entirely différent from the 

 former médium, Ihe individuals which appear dead will begin (o grow, and 

 even form slrong cultures. The nilrogen fixing bacterium, Azotobacter c/irou- 

 coccum, is a typical example of such a case. If this bacterium is cultivated in a 

 médium wilhoul nitrogen,or poor in nilrogen, ofler a relali\ely short period the 

 growlh of the culture is complelely slopped. If a new meiiium rich in nilrogen 

 is Ihen supplied, slrong growlh is renewed. 



According to the stage of developement moi-e or less imporlanl variations 

 in Ihe form of Ihe bacterium appear, for Azolobacler is subject lo morpholo- 

 gical change under Ihe influence of external conditions. 



Three chief forms may be dislinguished in normal develo[iemcnt ; Ihe rod- 

 shaped, the coccus and Ihe spore. 



The firsl is found during Ihe early stages of growlh and multiplicatidii. Ilic 

 second during Ihe fructificalion period when mulliplicalion may slill continue, 

 and Ihe Ihird is Ihe resling stage. Varions olher forms bave been observcd 

 al the différent periods of developement, but no absolute proof Ihat thèse dilïe- 

 rent forms are derived from one anolher, is available. Theorigin of Ihe isolaled 

 and exceplional forms from Ihe normal forms, and Ihe physiological part 

 played by Ihem, is nol known. Only by experimenis with cultures derived IVoiu 

 an isolaled single yeasl can thèse questions be salisfaclorily answered. 



If Ihe amounl of combined carbon in Ihe média of pure Azotobacter cul- 

 tures ismuch reduced,and small quantilies of asparagine are given in gradually 

 increasing amounts, forms of chroococciim and of i)lue-green alga, a|ipear which 

 are very near Ihe colourless form of Azotobacter in appearance. The question 

 whether Ihe Azolobacler is a pure species, or whether the formation of new 

 varielies and races is tnking place, musl be lefl lo the future to décide. 



Il miglil be suggested Ihal Ihe Leguminous bacteria would show analogous 

 physiological reactions lo Ihose shown by Ihc Azolobacler. Il is known Ihal Ihe 

 bacteria spécifie lo Ihe |i(',i, and lo bcans, is al Hrst inacti\e on IIk' mois ol' 

 Scrriiilellii and lupin, bul by successive cultures, Ihey may be adapled lo Ihc 

 new conditions, and linally Ihey may becoiue eslablished on Ihese jtlanis. 

 Récent researches hâve shown Ihat most likely certain ycasts (forms of Tu- 



