Introduction 11 



place, animal cells are for the most part sur- 

 rounded by a tough but mobile pellicle in place of 

 the rigid pellicle of the plant cell. Animal cells 

 can therefore be removed from the body with a 

 minimum of shock. Anyone who has worked with 

 both types will appreciate this difference. Ani- 

 mal cells adhere well to a variety of solid sub- 

 strata. They are capable of autonomous move- 

 ment and phagocytosis, so that they can be fed on 

 relatively complex nutrient materials which they 

 themselves transform into constituents which can 

 pass readily into the protoplasts. And finally, 

 "growth" of the animal body regularly takes 

 place in all parts of the body and, in the sense of 

 replacement, throughout the life of the animal. 

 There is thus comparatively little obvious restric- 

 tion placed on the experimenter in choosing favor- 

 able materials for cultivation. These facts have 

 largely affected the progress of tissue cultures 

 in the two living kingdoms and are responsible for 

 the early success in the animal field. Plant tissue 

 cultures have only within the last half decade 

 reached anything like a comparable position. 



SUMMAKY 



The question of the origin of form and function 

 in our Universe is one of the most fundamental 

 problems to the solution of which man has set his 



