CHOICE OF METHODS 6 



Tnals. The existence of a barrier protecting this fluid against the entry of anti- 

 bodies from blood plasma and thus making possible the growth of tumor trans- 

 plants, while all other tissues are resistant to their growth, has recently been 

 emphasized (Saphir, 0., Appel, M. and Strauss, H. A., Cancer Res., 1941, 1, 

 545-547). 



In order to view the less accessible living tissues, techniques have been devised 

 that include opening the body and partly withdrawing the organ so that it can 

 be placed on the stage of a microscope but with circulation and nerve supply 

 intact and adequate regulation of temperature and humidity. Particularly 

 fruitful has been the direct observation through oil immersion objectives of 

 secretion by acinous cells of the Pancreas by Covell (W. P., Anat. Rec, 1928, 

 40, 213-223) and of islet cells by O'Leary, (J. L., Anat. Rec, 1930, 45, 27-58). 

 Thus the influence of drugs on the secretory process can now be followed in 

 minute detail. 



Knisely (M. H., Anat. Rec, 1936, 64, 499-523; 65, 23-50) has perfected a 

 technique for the study of the living Spleen at somewhat lower magnification. 

 The essential features are shght displacement of the spleen so that it can be 

 transilluminated b}^ light delivered through a quartz rod. This allows for the 

 first time direct examination of the behavior of the venous sinuses. Undoubt- 

 edly the Quartz Rod technique will be of great service in providing light for 

 similar examination of other organs. 



3. To Study the Arrangement of Parts in the Body 



Since the body is structurally so very complex it is often illuminating to view 

 parts of it in their normal shape and size but unobscured by all the neighboring 

 components. There are several ways by which this can be accomplished. 



The first method of Reconstruction from serial sections is well known. Briefly 

 stated the particular tissue, organ or sj^stem is outlined, as it appears in section 

 after section, at the desired magnification on sheets of material of uniform and 

 carefully selected thickness. The outlined areas are then cut out and when 

 superimposed they constitute a reconstruction of the original structure. This 

 technique is tedious but it may reveal topographical relations that can be dis- 

 covered by no other means. 



The second kind of technique is to make casts of vascular, respiratory and 

 other lumina. Woods' metal, formerl}^ used for this purpose, has now been 

 almost displaced by Celloidin and other substances. The surrounding tissue is 

 freed from the cast by digestion in concentrated hydrochloric acid and gentle 

 brushing aw^ay in a stream of water. Very beautiful Corrosion preparations of 

 the lungs and kidneys have been obtained by this method which should be more 

 widely employed. 



The third is by Maceration to soak the organs, without previous preparation, 

 in fluids that either digest av/ay the tissues which it is desired to eliminate or 

 loosen their connections wdth those under investigation, which, latter, can then 

 be individually examined. Techniques of this sort are the only available means 



