214 BEHAVIOR OF ISOLATED CELLS 



3. Repeat either "1" ot "Z" but place the disarranged cells in calcium-free 

 Standard Solution and note the effect on amoeboid movement as well as cel- 

 lular aggregation. 



4. Cells may be separated from each other mechanically, with fine glass nee- 

 dles. This should be attempted, particularly with the later (neurula) stages 

 where the germ layers can be distinguished. 



5. 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 observe at intervals over a period of 2 or 3 days. Frequently there will 

 be complete re -organization of the neurula and development will be normal. 



6. Other solutions to be tested against neurulae to detern:iine their ability to 

 separate cells in a manner similar to KOH. Such solutions as K oxalate, 

 Na citrate, Ca-free Standard, and M/64 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. 



1. 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. 



2. 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. 



1. Calcium-rich Standard Solution. 



2. Calcium-free Standard Solution. 



3. 10% Standard Solution (hypotonic). 



4. Alkaline Standard Solution with pH above 9. 6. 



5. Neutral Standard Solution with pH at 7. 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 neuro- 

 blasts. 



