308 ALWIN M. PAPPENHEIMER 



longed time, one may sometimes note alternating phases of 

 activity and rest; during the latter phase, the cell assumes a 

 spherical shape. Multiplication of the cells does not take place 

 in vitro to an appreciable extent. On but two occasions was 

 actual division observed. One of the cells in a twenty-four-hour 

 culture, was first seen at 8.50 a.m. in a state of active amoeboid 

 motion. Sketches were made at one minute intervals. The cell 

 continued active until 9.47, crawling along the surface of an 

 adjacent large cell. At this time it went into a resting spherical 

 state, remaining inactive until 10.34 a.m. It then again became 

 active, throwing out long pseudopodia and changing its relative 

 position. At 10.45 it again became rounded and motionless. At 

 10.50 a shallow constriction was first seen dividing the cell into 

 two equal lobes. This rapidly deepened, and at 10.51, the sep- 

 aration was complete, division having taken place in less than 

 two minutes from the first appearance of the constriction. The 

 two cells remained close together until 11.20 when the observa- 

 tion was interrupted. At 1.30 p.m. they had moved apart and 

 could no longer be identified. 



The second cell came under observation first at 2.29 p.m. 

 Until 3.12 it continued to show active amoeboid motion; at this 

 time it became quiescent, remaining so until 4.01, when a slight 

 constriction was first noted. Division was complete at 4.05 and 

 ten minutes later, one of the new cells became active and moved 

 away from the other. During the division, a slight indication of 

 a spindle was noted, but the chromosomes could not be definitely 

 made out, and the mitotic character of the division could not be 

 established with certainty. In none of the fixed and stained 

 preparations could karyokinetic figures be found, although pic- 

 tures suggesting amitosis were plentiful. The proliferative capac- 

 ity of the lymphoid cells in vitro is therefore a limited one, and 

 multiplication occurs to a negligible extent. The cells retain 

 their vitality, however, for a considerable period, and amoeboid 

 activity has been noted after six days and probably persists even 

 longer. The majority of these cells are of small size and remain 

 indefinitely in an inactive spherical shape. They seem to become 

 denser and more refractile. 



