BEHAVIOR OF ISOLATED CELLS 205 



e. Separate the cells of a neurula within its external membranes by means of the KOH 

 Standard Solution, This should require from 10 to 60 minutes. When the cells 

 are fully separated, return the neurula to Standard Solution and ohserve at inter- 

 vals over a period of 2 or 5 days. Frequently there will be complete re-organl- 

 zatlon of the neurula and development will be normal. 



f . Other solutions to be tested against neurulae to determine their ability to sepa- 

 rate cells in a manner similar to KOH. Such solutions as K oxalate, Na citrate, 

 Ca-free Standard, and m/61+ KCN might be tried. 



FRAGMENTATION 



Isolated embryonic cells can be caused to fragment or pinch off knobs of protoplasm 

 or form blister-like protrusions by a variety of means. 



a. Observe an amoeboid embryonic neural plate cell which shows a passing wave of 

 constriction along its main axis. Gently handle this cell with a glass needle 

 and often the wave-like constriction will cut the cell into two. 



b. Chemical fragmentation of cells may be accomplished by means of hypertonic 

 (standard) solutions; alkaline media; pure sodium chloride solutions (isotonic); 

 and a variety of agents such as cysteine and alloxan. Such fragments should be 

 returned to Standard Solution and observed for the duration of activity, which 

 may be as long as 7 days. 



The best results will be achieved by treating the cells with KOH in Standard 

 Solution where the pH is raised to 10 or 11. 



ADHESIVENESS 



Embryonic cells are most adhesive immediately after their Isolation or separation 

 from each other. This adhesiveness is gradually lost even in Standard Solution. (See the 

 Glossary under such terms as cytotaxis, cytolisthesis, cytotropism. ) The developmental 

 stage of the cell and its histological type will also affect the degree of adhesiveness. 



Following the above procedure of isolating embryonic cells, place the isolated cells 

 in each of the following media to determine the effect of the medium on the tendency of 

 cells to stick together. 



a. Calcium- rich Standard Solution. 



b. Calcium- free Standard Solution. 



c. 105^ Standard Solution (hypotonic). 



d. Alkaline Standard Solution with pH above 9* 6. 



e. Neutral Standard Solution with pH at 7.0 to 9-0. 



PHAGOCYTOSIS 



This observation is rather difficult, but can be observed if the student has abundant 

 patience and can concentrate on endoderm, mesenchyme, endothelial cells and neuroblasts. 



The cells of a neurula should be isolated with 0.1^ KOH in Standard Solution and then 

 transferred to fresh Standard Solution (without KOH) to which some carbon or carmine par- 

 ticles have been added. Occasionally one will see the amoeboid-type of ingestion of the 

 foreign particles, a process similar to normal phagocytosis. 



DIFFERENTIATION 



The neurula-stage isolated embryonic cells in Standard Solution may be placed in a 

 culture dish or a depression slide and sealed with a rim of vaseline around the cover or 

 coversllp. All conditions must be aseptic. The cells will often survive from 2 to 7 days 

 and many will differentiate. 



