BIOLOGICAL METHODS 19 



significance of a given structural state is bound to the 

 knowledge of the corresponding physiological state. 

 Structure and function must be considered simultaneously.' 



Furthermore, tissues evolve in time. 



'A tissue consists of a society of complex organisms which 

 does not respond in an instantaneous manner to the changes 

 of the environment. It may oppose such changes for a 

 long time before adapting itself to the new conditions 

 through slight or profound transformations. To study it 

 at only one instant of the duration is almost meaningless. 

 The temporal extension of a tissue is as important as its 

 spatial existence.* 



The conception of cells and tissues which Carrel has sub- 

 stituted for the classical viewpoint is that of *a system: cells- 

 environment, of which the structural, functional, physical, 

 physico-chemical and chemical conditions are considered in 

 time as well as in space.* This constitutes a dynamic concept 

 beside the purely static concept of the old cytology. 



Physiology as a whole, one of the most fundamental 

 sciences of life, of which almost all the others are but chapters, 

 is essentially dynamic. Carrel's great merit has been to show 

 that outside of a general physiology which considers complete 

 organs preferably studied in vivo, a cellular physiology could 

 be created which, without encroaching on the domain of 

 general physiology, enables one to simplify the problems and 

 to study the individual activities of each of the elements 

 composing an organ. The name of * breaking-down methods* 

 which we employed in the beginning is thus justified. The 

 method of tissue-culture outside of the organism enables one 

 to go farther in the breaking-down process than does classical 

 physiology. To make a rough comparison, the study of an 

 automobile is divided into two stages. First, the study of the 

 role and workings of the organs in situ and their breaking up 

 as complete elements: dynamo, magneto, carburettor, motor, 



