Physiological histology, methods and theory / by Gustav Mann.

  • Gustav Mann
Date:
1902
Catalogue details

Licence: Public Domain Mark

Credit: Physiological histology, methods and theory / by Gustav Mann. Source: Wellcome Collection.

    27/524 page 5
    VIEWS OF AUTHOR than with any other fixative, the cytoplasm in plants1 appearing to consist of closely packed granules, the microsomes of M. Heidenhain, with the intermediate substance reduced to a minimum. About 1893 I commenced to realize that those reagents, which most thoroughly precipitate proteids in test-tubes, need not of necessity be the most suitable for preserving the delicate structures occurring in the cell. Picro-corrosive is the best mixture for completely and readily precipitating all proteid substances, but such vigorous precipitation causes many of the fine details in cells to disappear. To remedy this defect, which I attributed to exosmosis being caused by the high concentration of salts in the fixing solutions, I passed from saturated solutions to those having approximately the specific gravity of tissues, namely, 1,020. Since 1895 I have used combinations of the picro-corrosive mixture with osmium tetroxide and formaldehyde, because I believed these substances, by forming additive compounds with proteids, would render the cell more resistant. Now I consider all electrolytes, it being immaterial whether they be used singly or in combination with non¬ electrolytes, to have a tendency to produce artefacts, and for purely morphological purposes, if chemical substances have to be employed, I rely on the action of the non-electrolytes osmium tetroxide and formaldehyde dissolved in isotonic solutions of sodium chloride. From the above short summary of the results obtained by different observers, it would almost appear as if the task of investigating the structure of the cell was a hopeless one, and that we should never get any nearer the truth. Such a view, however, does not seem to be warranted. When investigating the anatomy of an animal, after studying first its outer aspect, we examine the general arrangement of its internal viscera, and do not start, for example, the study of human anatomy by contemplating the net-like arrangement of lines on the surface of the liver, and by speculating as to their probable cause. Similarly, in dealing with cells we should study in the first in¬ stance the coarse anatomy of the cell, namely, its nucleus, centro- somes, secretions, ducts, and specialized plasms as found in muscle, connective tissue, or epidermal structures, for all these elements may readily be seen in suitable, perfectly normal, living cells. Subsequently, by the addition of a fixing reagent we endeavour to preserve the appearances seen during life. If, in doing so, new structures are revealed, we have to determine whether these pre¬ exist, or whether they have been produced by the reagent employed. To settle this question a systematic use must be made of normal death, and that caused by the most diverse physical and chemical means, such as heat, cold, dehydration ; by acid, neutral, and alkaline media ; by oxidation and reduction, and the action of reagents forming additive compounds. All these means must further be tried not only on resting cells, but also on those which are in various phases 1 Mann, ‘ The Embryo-sac of Myosurus minimus. A Cell Study.’ Trans, and Proc. Bot. Soc., Edinburgh, 1892.
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