TISSUE-CULTURE IN VITRO IO9 



indication that the diet must be momentarily changed and the 

 concentration of the 'juice' modified. The cultures are some- 

 times even submitted to a period of fasting. The treatment to 

 be appHed differs according to the case, and there are no 

 precise rules. Everything depends on the experience and 

 'clinicar sense of the operator. 



The material organization of a laboratory for tissue-culture 

 is not very complicated. The difficulties which arise can gener- 

 ally be traced to the lack of rigorous care that must be given 

 to the slightest detail and the long experience that is necessary 

 to keep them in good health. 



The development of this science depends entirely on the 

 possibility of maintaining the principal types of cells in a state 

 of pure cultures. Carrel has demonstrated that this is 

 possible. The study of these cultures has revealed that each 

 cellular type is characterized not only by its morphological 

 aspect but also by an aggregate of special physiological proper- 

 ties. These properties remained unknown up till now because 

 they were hidden by the tremendous complexity of the pheno- 

 mena which take place in the organism. It is impossible to 

 know the physiological state of the cells and, consequently, 

 the significance of what is observed, if cells taken from a 

 living animal or an impure culture (mixture of cells of different 

 species) are studied by means of the old techniques as was done 

 and is still done by certain workers. It is only by means of 

 colonies composed of a single-cell type, placed in flasks con- 

 taining a medium of known composition, and manifesting a 

 measurable form of activity, that it becomes possible to 

 establish a relation between the morphological state (as seen 

 under the microscope) and the functional state of the cells. 



The culture of tissues has already considerably increased 

 our knowledge of cell physiology, and we are only at the 

 beginning. For in spite of tlie fact that this method is already 

 fairly old, there are few scientific centres where it is employed. 

 This is due to the difficulties mentioned above, to the expense 

 involved, and to the fact that, to be fruitful, it requires real 

 talent, great manual dexterity, patience, and imagination. 



