THE MICKOMANIPULATION OF LIVING CELLS 



27 



tor of the cleava<it' furrow will ])ee-oine 

 more nearly spherical when the i)res8ure ex- 

 erted b}' the cleavage furrow is relaxed, in 

 case cleavage has been unsuccessful. When 

 the oil drop is pinched in two by the com- 

 pletion of the constricting furrow, the suc- 

 ceeding portions of the oil di-oj) become 

 spherical, to be deformed again during the 

 following cleavage (Chambers and Kopae 

 1937). 



(f) Finally, we have the observation 

 mentioned by Costello (1938) that natu- 

 rally occurring oil drops in Nereis eggs will 

 coalesce on contact following sperm-activa- 

 tion of the eg'^. 



The low value of the })ositive interfacial 

 tension between oil and internal protoplasm 

 may be ascribed to the In-drated protein 

 molecules which are assumed to be the chief 

 components of the protoplasm. It is well 

 known that native proteins are extremely 

 surface active at oil-water interfaces. For 

 this reason, proteins are commonly used as 

 emulsifying agents. Since the oil-proto- 

 plasm interfacial tensions are of the same 

 order of magnitude as those of oil-water 

 (protein) interfaces, the conclusion that 

 protein molecules are responsible for the 

 low oil-protoplasm interfacial tensions 

 seems justifiable. It might be added here 

 that the oil-protoplasm interfacial tensions 

 are many times lower than would be ex- 

 , peeted on the basis of pH and salt content of 

 of the cytoplasm alone. 



When protoplasm is caused to undergo 

 cytolysis, the interfacial tension becomes 

 zero and spontaneous deformation of the 

 oil drop ensues. An ingenious method de- 

 veloped by Kopae (1938) to show this is 

 the drop-retraction method, in which the 

 injected oil drop, after being allowed to 

 reach a given size, is gradually diminished 

 in volume by withdrawal of some of the oil 

 into a pipette whose tip has been kept in 

 contact with the drop. If adsorption of 

 substances, for example, proteins, has oc- 

 curred only partially on the drop, the drop 

 may be decreased in size wdthout becoming 

 deformed until a critical diameter is 

 reached. Diminishing the drop correspond- 

 ingly reduces the interfacial area and a 



concent I'ation of adsorbed molecules takes 

 ])lace. The condition is analogous to that 

 which occurs in the reduction of area on a 

 Langmuii* trough by moving a barrier 

 across the surface. Wlien ])roteins are ad- 

 sorbed at oil-water interfaces, the Devaux 

 effect (crinkling) ai)pears when the inter- 

 face is covered Avith more than enough pro- 

 tein to foi-m at least one monolayer. Ac- 

 cordingly, at the threshold of the Devaux 

 effect the critical diametei- indicates that 

 the oil drop is coated by at least one layer 

 of protein. 



Striking ()il-proto])lasmic interfacial ef- 

 fects are produced by using certain fish- 

 liver oils, also certain plant oils, against the 

 protoplasm of Asterias eggs. In the intact 

 cytoplasm, the drops remain spherical and 

 clear-cut as long as the oil causes no per- 

 ceptible injury to the cytoplasm. However, 

 a pronounced reaction occurs when the oil 

 is introduced into a cell and cytolysis is 

 induced immediately thereafter. Within 

 30 seconds after the cell has cytolyzed, the 

 Devaux crinkling effect appears spontane- 

 ously on the oil drop (Kopae 1938). 



The contrast between the lack of a visible 

 reaction of adsorption to the above oils in 

 living protoplasm, and the pronounced re- 

 action occurring on death or shortly there- 

 after, is very significant. Since proteins 

 constitute the greater part of protoplasm, it 

 is to be concluded that the state of the pro- 

 teins in the living cell is very diff'erent from 

 that of the proteins in the dead and dis- 

 integrated cell. 



For these ex})eriments, the immature 

 oocytes of Asterias are particularly useful. 

 Cj'tolysis or disintegration of the egg oc- 

 curs merely by puncturing the germinal 

 vesicle with a microneedle. Hence, follow- 

 ing the cytoplasmic injection of a suitable 

 oil, cytolysis can be readily induced at will, 

 and the effect on the oil may be instantly 

 observed. Under such conditions, the 

 crinkling and subsequent distortion of the 

 oil drop is spontaneous, denoting a spon- 

 taneous increase in the interfacial area be- 

 tween the oil and cytolyzed residue. Such 

 spontaneous increase in interfacial area is 

 obviously possible if the interfacial tension 



