LIFE-HISTORY OF AMOEBA PROTEUS. 415 



changes of distilled water. Alter this there was added each day 

 for food about 5 cc. ot fresh sterile culture fluid like the original 

 culture fluid. All pipettes used in handling the amoeba and the 

 culture fluid were repeatedly sterilized in order to eliminate 

 contamination. 



The culture was poured into a sterile shallow dish and thor- 

 oughly examined every few days. It was found that the indi- 

 vidual multiplied by fission until in about two weeks there were 

 perhaps fifty large amoeba; in the culture. Then fission appeared 

 to cease and the amoebae assumed a dark granular color, after 

 which they began rapidly to disappear so that by the end of the 

 third week there were no large amoebae present. If there had been 

 one large amceba left it could not have escaped the rigid inspection 

 to which the culture was subjected. The culture was now set 

 aside for a week, after which it was again examined. It now con- 

 tained numerous small amcebae the length of which varied from 10 

 to 40 ju, but no large amoebae. For over a month tollowing this 

 the culture was repeatedly closely observed. The amoebse in- 

 creased in size until by the last of April there were numerous 

 specimens which measured 300-600 IJL in length. 



On September 17, 1926, fourteen cultures made up in a modi- 

 fied Ringer's solution were inoculated with amoebae from an ordi- 

 nary spring water culture after being washed in six changes of 

 the Ringer's solution. At the end of four days all of the large 

 amoebae had disappeared and soon after this small amoeboid forms 

 were observed in great numbers. From this time on the cultures 

 were thoroughly examined at the end of each week and after each 

 examination camera lucida sketches were made of the largest 

 amcebae found in each culture. Some of these sketches are here- 

 with reproduced (Fig. i). They show that the amoeboid forms 

 increased from an approximate average volume of 400 cubic 

 micra to one of 250,000 cubic micra and that this increase re- 

 quired two months. During this time, however, it was observed 

 that these small amoebae occasionally divided (Fig. 2). All of 



small amoebae produced by fragmentation of original large amoebae; 3, largest 

 amoebae in culture ten days after fragmentation; 4, largest amoebae in culture four 

 weeks after fragmentation; 5, largest amcebae in culture six weeks after fragmenta- 

 tion; 6, largest amoebae in culture eight weeks after fragmentation. 



