XVlll CHOICE OF METHODS 



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

 stated the particular tissue, organ or system 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, formerly 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 away 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 away the tissues which it is desired to eliminate or 

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

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

 for the isolation of individual seminiferous and renal tubules. Oliver's researches 

 on the kidney illustrate the value of reconstruction and maceration in pathology. 

 Only three other examples will be submitted. Thyroid follicles can be isolated 

 by maceration (Jackson, J. L., Anat. Rec, 1931, 48, 219-239). Their study as 

 individuals provides data as to size and shape only obtainable otherwise by the 

 tedious examination of serial sections. The Epidermis is so tightly bound to 

 the underlying dermis that separation is extremely difficult; but, after treatment 

 of skin with dilute acetic acid, the attachment is loosened and the epidermis can 

 readily be removed as a complete sheet of tissue which can be stained, made 

 transparent and examined as a whole mount. Opportunities are thus afforded 

 for the detection of regional differences which might not be located even by pains- 

 taking study of sections and the making of mitotic counts is greatly facilitated. 

 By macerating in the same fashion the nasal mucous membrane covering the 

 septum can also be removed for study. Perhaps still other epithehal sheets can 

 be similarly isolated. However such sheets are of Httle value for chemical 

 analysis because of the action of the acetic acid. Fortunately it has been found 

 that the epidermis may also be quickly loosened by simply heating the skin 

 to 50°C. when it can be peeled off like the covering of a scalded tomato (Baum- 

 berger, J. P., Suntzeff, V. and Cowdry, E. V., J. Nat. Cancer Inst., 1942, 2, 

 413-423). 



There is still another alternative. Instead of simply omitting the unwanted 

 material by reconstructing only the structures chosen for demonstration, or of 

 removing the material by corrosion or maceration, it can be left in and rendered 

 transparent so that it does not obstruct the view. After marking the particular 

 structures by vital dyes or other means the whole tissue is cleared by the method 

 of Spalteholz or Schultze. These techniques give admirable results in the study 



