THE BIOLOGY OF THE CELL SURFACE 



treat the organisms on which they work, "material" 

 as they call them, that they prefer their living systems in a 

 debased and degraded condition. 



Surely, of all biologists the investigator who experiments 

 on eggs needs to exercise most scrupulous care in order to be 

 sure that the cells under investigation are in optimum 

 condition. In the investigation of a system of organs, an 

 organ or even a tissue, like nerve or muscle, although one 

 can never be absolutely certain that all cells present are 

 normal, the high number of cells that compose such a 

 structure guarantees a high number of normally reacting 

 cells and thus increases the probability of a normal response. 

 In the case of eggs, one deals with structures which are 

 single units, individuals that show each its own state of 

 normality or abnormality. Furthermore, whilst it is true 

 that out of each egg arise cell-complexes — tissues, organs, 

 and organ-systems — these differ so much in degree of 

 activity, in time of origin and in relation to each other in 

 space, that the determination of the normality of the 

 developing ^^^^ made up at a given stage of a number of 

 cells equivalent to that in a given tissue with which com- 

 parison is made, is more difficult than in this tissue. The 

 developing egg is normal only if all these different com- 

 plexes present are normal. But this necessity of careful 

 investigation of the grade of normality in eggs has one 

 important compensation which makes the study of eggs so 

 fruitful for biology. The behavior in laboratory experi- 

 ments of tissues, e.g., nerve, muscle, or tissues in culture, 

 removed from an organism may not at all be the same 

 as that in the intact organism. That countless investiga- 

 tors have obtained the same laboratory results speaks on 

 the one side for the excellence of laboratory procedures, 

 on the other for the wonderful capacity of tissues removed 

 from an animal's body to withstand experimental treat- 



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