December 31, 1915] 



SCIENCE 



939 



not strange that the protozoan fauna lacks 

 uniformity. The chemical decompositions in 

 the soil itself, its gaseous content, the antag- 

 onisms of certain salts, the demands upon the 

 soil hy its superterranean flora, the fluctuating 

 bacteria and molds, the ravages of nematodes 

 and the tosin and excreta of all of the organ- 

 isms living therein and thereon, all form a 

 part of the agencies potent in modifying, stim- 

 ulating or depressing the protozoan fauna as a 

 whole, and its several elements differentially. 



One of the principal points brought out by 

 recent investigations has been the relative 

 numbers of flagellates and amcebas, the main 

 interest centering in the latter because of 

 their possible action as bacterophages of bac- 

 teria active in fixation of atmospheric nitro- 

 gen. The late 0. H. Martin, vs^hose death at 

 the Dardanelles is an irreparable loss to the 

 science of protozoology, has shown (1912) 

 that one flagellate, Monas termo Ehrbg., is as- 

 sociated with the occurrence of certain " sick 

 soils " in Great Britain, but little precise work 

 has been done as yet elsewhere upon the flagel- 

 lates of the soil. 



Two papers published recently are typical 

 of the divergences of results with respect to 

 the relative abundance of amoebas and flagel- 

 lates in the normal fauna of soils. Cauda and 

 Sangiorgi (1914) in soils from rice localities 

 find that amcsbas are the prevailing forms, 

 were present in all localities, and were ex- 

 ceeded in numbers by the flagellates in one 

 case only. Flagellates together with the cili- 

 ates were sometimes entirely absent. On the 

 other hand, Sherman (1914) concludes that the 

 active protozoan inhabitants of most soils are 

 probably restricted to the flagellates, that they 

 constitute the greater portion of the protozoan 

 fauna of the soil, and that the amoebas do not 

 ordinarily occur in numbers nearly as great as 

 do the flagellates. Both of these conclusions 

 may well be correct for the soils examined, but 

 I wish to cite facts which necessitate caution 

 in making sweeping conclusions from such 

 data and to set forth a new factor not as yet 

 considered, in so far as I can infer from the 

 literature, by any investigator of soil proto- 

 zoa. The absence of its consideration tends 

 to weaken or possibly even to vitiate conclu- 



sions as to relative numbers of amcebas and 



Certain investigations carried on in my 

 laboratory by Dr. Charlie W. Wilson (1915) 

 on the life history of a soil amffiba have a di- 

 rect and, it seems, an important bearing on 

 this problem of the seeming relative numbers 

 of amoebas and flagellates. I use the term 

 " seeming " advisedly for the investigations 

 prove that the common soil amoeba, Nrngleria 

 gruberi (Schardinger), has a biflagellate 

 phase, and enflagellates and exflagellates 

 rather quickly on slight provocation under the 

 conditions of laboratory culture. Not only do 

 single individuals undergo these transforma- 

 tions but the whole mass of the culture may do 

 so. The bearing of this fact upon the re- 

 ported difference in the flagellate and rhizopod 

 components of the protozoan fauna of the soil 

 is self-evident. 



This amceba (Fig. 1) is a small organism 

 (8 ft, to 30 ju,) with one broad blunt pseudo- 

 podium or sometimes several blunt ones, and 

 one subcentral nucleus. When it enflagel- 

 lates the karyosome sends out a chromatic 

 process (Fig. 2) which traverses the nuclear 

 membrane, forms a marginal blepharoplast, 

 and emerges as two long flagella (Figs. 3, 4). 

 The body assumes a rigid asymmetrically 

 curved shape and the organism swims away in 

 the typical spiral course. When it exflagel- 

 lates the flagella shorten and thicken and re- 

 treat into the cytoplasm and the blepharoplast 

 returns to the karyosome within the nucleus. 

 It takes about 70 minutes for a culture of 

 amoebas to become one of flagellates, while the 

 reverse process is somewhat longer and less 

 uniformly followed by the individuals in the 

 cultures. The addition of water, or fresh cul- 

 ture medium (filtered and sterilized soil and 

 manure infusion) or the access of air, tends 

 to induce enflagellation, but exflagellation is 

 less definite in response to their opposites. 

 Fission, budding, encystment, excystment and 

 chromidial extrusion occur frequently and 

 rather quickly. 



These processes and the flagellate stage are 

 evidently adaptive phenomena fitting this or- 

 ganism to a life in the soil with its vicissi- 

 tudes of fluctuating food supply, alternations 



