l8 THE BIOLOGICAL PROBLEM 



reconstitute exactly the architecture of the cell. The selective 

 dyes are indispensable to show up the structural details which 

 are otherwise invisible owing to the similarity of their refrac- 

 tive index, the absence of natural colour, and the thinness of 

 the sections. Broadly, cytological and histological techniques 

 consist in fixing, i.e. killing, the cells without deteriorating 

 them and then colouring these sections by means of 

 different substances (aniline dyes, for instance, or metallic 

 impregnations). 



We will not dwell on these methods which have rendered 

 and continue to render great services. We will only point 

 out that the purely morphological study of anatomical and 

 cellular elements cannot furnish any information as to their 

 physiological functions. 



Dr. Alexis Carrel writes:^ 



*The structure of tissues and their functions are two 

 aspects of the same thing. One cannot consider them 

 separately. Each structural detail possesses its functional 

 expression. It is through physiological aptitudes of their 

 anatomical parts that the life of the higher animals is ren- 

 dered possible. Likewise, the life of a community of ants 

 depends on the physiological aptitudes of the individuals 

 of which it is composed. When cells are considered only 

 as structural elements, they are deprived of all the properties 

 that make them capable of organizing as a living whole. 

 Within the organism, they are associated according to 

 certain laws. Cell sociology results from properties specific 

 to each type of cell. Among these properties some manifest 

 themselves under ordinary conditions of life, while others 

 remain hidden. Tissues are endowed with potentialities far 

 greater than those which are apparent. But these poten- 

 tialities become actualized only when certain modifications 

 of the internal environment occur, as, for instance, when 

 pathogenic agencies are at work within the body. The 



' A. Carrel, 'The New Cytology', Science, vol. 73, no. 1890, pp. 

 297-303 (1931)- 



