W. F. LOOMIS 357 



plains their usual habitat which is the partially anaerobic 

 environment of the hypolimnton (2) as well as their 

 demand for the microaerophilic environment of a soil- 

 manure culture ( 1 ) . 



Amoeboid motion. 



Amoeba proteus and Chaos chaos are both far larger than 

 the usual metazoan cell. Their central protoplasm would 

 become extremely anaerobic if it did not liquify and then 

 flow peripherally in long pseudopods with a high surface/ 

 volume ratio. The possibility that amoeboid motion results 

 from this automatic gel-to-sol transformation under the 

 high pCOo (and consequent low pH) existing in the 

 center of these animals is supported by the experimental 

 finding that a pCOo of 20% atm. "melts" their pseudopods 

 back into their bodies so that they become spherical in 

 form. With time, continued respiration would re-establish 

 the inward-outward gradient of pCO^, and hence normal 

 amoeboid motion should recommence. In fact, it does 

 just this, but only if oxygen is present. Furthermore, 

 amoebae can crawl for days in the presence of 10 ~' M 

 dinitrophenol which is known to uncouple oxidation from 

 phosphorylation at this concentration (22) and so sug- 

 gests that it is the COo from respiration rather than the 

 ATP that is important in amoeboid motion. Finally, 

 Pantin showed with neutral red that the anterior and sides 

 of an advancing pseudopod were bright red (acid) and 

 that the color was stronger the more active the pseudo- 

 pod. This was especially the case with eruptive pseudo- 

 pods. 



The acrasin problem. 



The slime molds grow as many separate amoebae and 

 then aggregate by chemotaxis in response to the mutually- 

 produced but unidentified chemical named "acrasin" by 

 Bonner (3). Some preliminary experiments suggest that 

 the highly labile stimulus may be simply pCOo. With this 

 goes the possibility that high levels of pCOo in the 

 center of the multicellular pseudoplasmodium stimulate 



