BY E. N. WILLMER
Physiological Laboratory, University of Cambridge
Tissue culture in its various forms has been widely practised now for more than fifty years and this may be an opportune occasion upon which to examine its uses and abuses, and to attempt to relate the information obtained by the study of isolated tissues to that obtained by the study of the same tissues in the body. Until recently, when it was realized that tissue-culture cells form a suitable environment for the growth of viruses, the methods of tissue culture were chiefly applied to cytological, biochemical, embryological and morphological problems, and the results of these investigations will form the basis for most of the discussion which follows. It will be convenient to examine the methods and the results obtained by them in each of these connexions in turn, though some of the observations and conclusions may naturally apply to other branches, besides the one under discussion.
For cytological studies on the living cells, the cells of a tissue are generally placed in a suitable 'growth-promoting' medium and encouraged to creep out onto a suitable transparent surface, e.g. glass, cellophane or other wetable substance, so that they can there be examined under the highest powers of the microscope and with all the modern devices of polarized light, phase contrast, dark-field illumination and so on. They may be photographed with the ciné-camera, and the movements of all their constituent parts analysed in great detail. Cell division can be followed as a living process, both by direct observation and by some form of time-lapse photography. The effects of various reagents on the living cytoplasm and nucleus can be studied at particular phases in the mitotic process, or at specific times in the cycle of activity of the cells. It is true that, in tissue cultures of this kind, the meta- phase plate of chromosomes in mitosis is always seen from the side and cannot easily be observed from the direction of the poles of the mitotic spindle, but this is a small disadvantage as compared with the great gain of being able to follow the process of mitosis as it actually takes place, and of being able to subject it to various experimental procedures. At first sight, it appears that there is everything to be gained by studying cells thus isolated into tissue cultures.
It is, however, necessary to examine the cells which are being studied in this manner in a rather more critical way. Generally they are embryonic cells, because these 'grow' most easily, and are most readily obtained without