8 CHOICE OF METHODS 



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

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

 illumination and in the 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 

 others. Intracerebral and intratesticular inoculations are often made and, 

 again, young animals are in general most susceptible. 



The culture of Bacteria and Protozoa has for generations been a fine art based 

 on meticulous study of their needs. These relatively simple organisms provide 

 wonderful material for the investigation of the most basic of vital phenomena. 



7. To Investigate Composition by Chemical Means 



This cannot be done blindly — by just taking a chunk of tissue and analysing 

 it. The investigations must be guided by knowledge of the structure and func- 

 tion of the materials analysed. Blood can, for example, be collected in suf- 

 ficient volume for routine chemical analysis; but the results will differ depending 

 upon whether it is arterial blood, portal venous blood from the intestines, or 

 venous blood from the extremities. Analyses of whole skin are practically 

 worthless because the skin is a structure made up of two parts: avascular epi- 

 dermis of ectodermal origin and underlying dermis made up of connective tissue 

 difi"ering in vascularity, fiber, fat, tissue fluid and gland contents in various 



