10 Plant Tissue Culture 



medium in a way that seldom occurs in nature, it 

 greatly increases the shock which any cell must 

 inevitably suffer in the process of removing it 

 from the body. In the third place, "growth," in 

 the plant, is normally restricted to a few special- 

 ized regions of the body, leaving all other parts in 

 an essentially inert condition, as far as capacity 

 for continued cell multiplication is concerned, and 

 greatly restricting the experimenter in his choice 

 of materials. As a result of these difficulties, 

 although the problem has been investigated by a 

 considerable number of workers, more than 30 

 years elapsed between Haberlandt's formulation 

 of the tissue culture concept and the first really 

 successful experiments with plant tissue cultures. 

 Fortunately for the development of the field as 

 a whole, however, animal tissues present none of 

 the above-named difficulties, at least to anything 

 like a comparable degree. In the first place, ani- 

 mal cells throughout the body are regularly bathed 

 in one or both of two characteristic and essentially 

 complete nutrient fluids, the blood and lymph. 

 These can be easily removed from the body in 

 large quantity. They serve as basic "natural" 

 nutrients for animal cells in which such cells can 

 be immersed without serious shock. They can be 

 analyzed at leisure to determine which of their 

 constituents are truly essential. In the second 



