XXll CHOICE OF METHODS 



Thus cells can be grown in Tissue Cultures of chemical composition suited to 

 their requirements. Mixed cultures are those containing several types of cells 

 and pure cultures those containing but one sort. This technique affords un- 

 rivalled opportunities for experimentally changing the fluid environments of 

 cells, for the study of nutritional factors, growth stimulating and growth in- 

 hibiting factors, and the influence of cells on one another. Individual cells can 

 be observed at high magnification and the phenomena of motility, phagocytosis, 

 mitosis, cell death, etc. can be recorded by moving pictures so that the analysis 

 of form and function is possible with a high degree of accuracy. 



The limitation of the method is the obvious one that the fluid environments 

 are artificial and must be changed at intervals to keep the strains of cells alive. 

 Consequently tissue cultures are unsatisfactory for the investigation of inter- 

 cellular materials, like fibers, hyaline deposits and so on. Moreover the cells 

 cannot properly organize to form tissues and organs as they do in vivo since they 

 are isolated from normal influences by other tissues of the body. But they 

 make the effort. Methods have recently been advocated for the culture of 

 organized tissues, bones, teeth, etc. (Fell, H. B., J. Roy. Micr. Soc, 1940, 60, 

 95-112). 



In selecting the technique of tissue culture for the solution of any problem 

 it is well to remember that considerable equipment and several years training 

 are required to realize its full usefulness. For this reason valuable time will be 

 saved by learning the technique from an expert. 



The new and highly productive technique of analysing cellular responses by 

 their observation in Motion Pictures offers more attractive leads when applied 

 to living cells in tissue cultures than to cells viewed in other situations. In 

 tissue cultures they can be photographed at high magnification, both by direct 

 illumination and in ths dark field, because they occur as individuals or as thin 

 clumps in the fluid. Moreover, their behavior can be followed in successive 

 photographs over long periods of time and it is possible directly to observe how 

 this is modified by a host of different influences experimentally brought to bear 

 on them. For teaching Motion Pictures are helpful, but can be used too much. 

 Easy come, easy go is true of instruction. Unless learning is combined with 

 some sort of effort it will be of very transitory value. 



Transplantation of tissue from its original location to a new and different 

 position, such as the Anterior Chamber of the Eye, is also a culture method of 

 value in the solution of certain problems. The factors that condition the growth 

 and the behavior of the transplant are of importance. 



Some organisms can best be grown, and viruses increased in amount, by 

 implanting them into the Chorioallantoic Membrane of chick embryos. This 

 technique has abundantly proved its worth. The feasibility of culture in this 

 membrane depends essentially on the lesser development of growth inhibiting 

 factors in young tissues than in older ones. 



Viruses will "take" and increase in amount in some locations better than in 



