418 COLLOIDS IN BIOLOGY AND MEDICINE 



shrinking. Pure water is never suited for this; a salt solution 

 which approaches in its composition that which bathes the organ is 

 best. In many cases "physiological salt solution" is ample; in 

 mammals this contains 0.85 per cent common salt, in other kinds of 

 animals this may advantageously be reduced to 0.5 per cent. Even 

 though the living or surviving organism presents a microscopical 

 picture devoid of artifacts, on the one hand it is rarely possible to 

 examine it and, on the other, many details are concealed, since the 

 refraction of the different cell elements is almost equal. On this 

 account we are compelled to section and stain the organs. 



Since even the death of the cell causes changes in structure, these 

 changes with the chemical manipulations about to be described 

 may reach a grade which leads to the gravest errors. Only absolute 

 ignorance of colloid processes explains how artificially produced 

 flocculations, coagulations and striations (after treatment with 

 silver nitrate and potassium bichromate), etc., could be considered 

 definite constituents of cells, and it is a pity that numerous pains- 

 taking investigations must, as a result of this, be considered mere 

 waste paper. By indicating these errors A. FISCHER and WALTHER 

 BERG, as well as TH. v. WASIELEWSKI, performed a great service. 

 Accordingly, A. FISCHER distinguishes reagents which form granules 

 (nuclei) and those which form coagula, and W. BERG also calls at- 

 tention to those which produce granulated pellicles and cavities. 



If then, as may be seen from the foregoing, we may obtain different 

 structures by means of different reagents acting on the same bodies 

 and, conversely, with the same chemical substance produce the same 

 microscopic picture on different bodies, we may by accurate com- 

 parative experiments make valuable deductions. It is hardly possible 

 to employ such methods in determining form, but for the understand- 

 ing of the colloidal nature of the object examined they offer a broad, 

 uncultivated and promising field for colloid research. 



The preparation of dead material for microscopic examination may 

 be divided into maceration and isolation, fixation and hardening, 

 decalcification, bleaching, embedding, sectioning and mounting, and 

 finally staining. 1 



Maceration and Isolation. 



Maceration and isolation are for the purpose of dissolving apart 

 the constituents of an organ (cells) and thus to recognize their con- 

 nection and to make it possible to examine the isolated cells. The 



1 I have for the most part followed here the directions given in the "Lehrbuch 

 der Mikroskopischen Technik" of Prof. Dr. B. GRAWITZ (Leipzig, 1907), whose 

 numerous detailed directions should be of valuable assistance to every biochemist. 



