4 CHOICE OF METHODS 



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 exammation of serial sections. The Epidermis is so tightly boimd 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 epithelial sheets can 

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

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

 that the epidermis ma}'' also be quickly loosened bj'' 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 bj'' the method 

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

 of Cartilaginous Skeletons, Ossification centers. Blood Vessels and so on almost 

 without end. 



4. To Employ the More Routine Method of Fixation and Staining 



Here there is wide latitude of choice. For some purposes thin Smears are 

 just fixed and stained without resort to sectioning. In the case of the denser 

 tissues which must be cut in sections one first has to decide which of many 

 Fixatives is likely to give the best results. Then, whether fixation is to be by 

 immersion or injection has to be determined. 



The purpose of fixation by vascular injection is to bring the fixative into close 

 contact with the tissues as they exist in the freshly killed animal without sub- 

 jecting them to mechanical trauma or disturbing their topograpliic relations one 

 to another. In choosing this procedure it is well to remember: (1) That it is 

 usually necessary first to wash out most of the blood by perfusion with physio- 

 logical salt solution for otherwise the fixative often clogs the vessels. This wash- 

 ing unfortunately also facilitates chemical change. (2) That, even when it is 

 not done, the concentration of the fixative about the cells is gradually increased 



