340 MARGARET R. LEWIS AND WARREN H. LEWIS 



INTRODUCTION 



Tissue cultures afford a new and somewhat different method 

 from that usually emj^loyed for the study of many cell struc- 

 tures. It enables one to compare the living with the fixed mate- 

 rial. In fact, one can study the same cell while living, during 

 the process of fixation, and later as a stained permanent prep- 

 aration. It also enables one to follow the changes which take 

 place in the living cell from minute to minute. Above all, tissue 

 cultures afford a method by which we can experiment on the 

 cells and mitochondria. And through such methods only do 

 we believe a correct interpretation of the significance of mito- 

 chondria is to be found. 



In spite of the new and different enviromnent of the tissue, 

 i.e., its isolation from the rest of the embryo; the substitution 

 of a simple Locke's solution for normal plasma; the contact with 

 the cover-slip; and the absence of a circulation, which continu- 

 ally renews the food-supply and removes the waste, the cells 

 of the tissue cultures are apparently quite normal during the 

 first two or three days and exhibit no noticeable changes except 

 the characteristic configuration of the growth. How greatly the 

 new environment disturbs the normal metabolic processes of the 

 cell is impossible to surmise. The cells are in such a thin layer 

 that each cell is probably as well bathed by the Locke's solu- 

 tion as in the embryo it would have been bathed by plasma 

 or lymph. 



In the older cultures the cells lose their normal appearance 

 and show signs of degeneration. Migration, growth and mitosis 

 cease, the cells become smaller and show both cytoplasmic and 

 nuclear changes. This may be due to the fact that the medium 

 lacks both the inorganic and organic substances necessary for 

 the prolonged continuance of life, but when we consider that the 

 same degeneration takes place when tissues are explanted into 

 a plasma medium it seems more probable that the degener- 

 ation is due to an excess of waste products accumulated around 

 the cell. 



