THE BIOLOGY OF THE CELL SURFACE 



But let us for the moment dismiss badly fixed eggs, 

 pictures of fenestrated or lacunar substance, also the empty 

 spaces previously occupied by oil and yolk, and extend the 

 meaning of the word alveoli to embrace such Inclusions as 

 oil-drops and yolk-bodies seen in the living e^g as discrete 

 spheres. How far does this assumption strengthen the 

 alveolar theory of protoplasmic structure? Can we con- 

 clude that Inasmuch as each "alveolus" (oil-drop or yolk- 

 sphere) Is laid down by the egg during its history, an egg In 

 that stage before oil or yolk is deposited as easily visible 

 discrete spheres has no structure? Shall we say that In 

 those eggs which distribute their "alveoli" in such manner 

 that some cells possess all the "alveoli" and others none, 

 those cells which do not contain them are structureless ? 



The alveolar theory has found support from the fact that 

 certain artificial mixtures resemble some kinds of proto- 

 plasm. Witness emulsified oil. If we examine under the 

 microscope a thin layer of mayonnaise — olive oil and 

 vinegar plus egg-yolk, the emulsifying agent — we find that 

 the oil is in drops and among them are scattered yolk- 

 spheres. By carrying the process of emulslfication further 

 and further, we obtain smaller and smaller oil-drops and in 

 this way make structures that resemble those of eggs with 

 larger or smaller oil-drops. Such a film of mayonnaise 

 when fixed by a proper agent for cytoplasmic fixation 

 retains faithfully Its appearance before fixation and 

 simulates the picture of properly fixed egg-cytoplasm. The 

 emulslfication obtained by beating olive oil with vinegar or 

 lemon-juice, without egg-yolk, though less permanent, 

 bears also a close resemblance to the living cytoplasm of a 

 living egg, say that of a star-fish. It has even been held 

 that protoplasm Is a foam-structure because of the resem- 

 blance of some cellular structures to such foams prepared in 

 the laboratory. As I see It, all that these and similar 

 models tell is that the living cell can hold Its oil In the form 



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