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.

    29/524 page 7
    EFFECT OF NON-ELECTROLYTES and masses are to be obtained, with no indication whatever of a net or foam, when colloids are subjected to special conditions of stress or strain. Monckeberg and Bethe have further found white of egg fixed for forty-eight hours in the vapour of osmium tetroxide to be perfectly homogeneous, an observation bearing out my own. Formaldehyde free from formic acid also fixes homogeneously. It being thus possible to fix colloids in a homogeneously granular or foam-like manner, it is natural to choose primarily those reagents which produce the least visible alteration in media we know to have been homogeneous before fixation, because the less violent the change in a uniform medium the more completely also will be pre¬ served those delicate differentiations existing normally in a cell. Just now it was assumed that homogeneous mixtures do exist, but when we see produced a net, or foam, or granules, in what appears to us before fixation a homogeneous mixture, have we any right to sup¬ pose that such a mixture is in reality without structure ? I doubt it. When gelatin jelly sets at any given temperature, as soon as the percentage of water is reduced to an amount proportional to the temperature, we may assume either that an aggregation (polymeriza¬ tion) of the gelatin molecules has taken place, or that each gelatin molecule having become less mobile maintains its individuality, and that it touches its neighbour. As the gelatin molecules are larger than those of water, it is legitimate to suppose (not taking into account the intramolecular absorption of water) that the gelatin in the jelly state forms a double net consisting respectively of gelatin and water molecules, a view also supported by the rate of diffusion and ionic migration being the same in gelatin as in water. If this conjecture be true, then the appearances which we see in ‘ fixed ’ gelatin represent an exaggerated picture of the normal con¬ dition. Further, as the network which is formed by reagents is in most instances so close as to necessitate, for its clear demonstration, sections not exceeding 1-5 /z in thickness, we may readily, by cutting a section 2-5-5 f1 in thickness, reproduce the 1 homogeneous ’ appear¬ ance of unformed matter to the advantage of the formed or structural elements in the cell, which under these conditions will stand out clearly. Although for the general fixation of a cell those coagulants are best which give a homogeneous fixation, I believe it justifiable to use also reagents which do not preserve every cell-constituent. When we study the configuration of bones, we remove the muscles and other soft parts as completely as possible ; whe-n we desire to study the brain, the skull-bones are sacrificed, and we should proceed analogously with the study of the cell. After having studied the appearances in tissues fixed by reagents which act homogeneously, do not let us be afraid of using fixatives which cause artificial appear¬ ances in homogeneous solutions of proteids, as long as we know definitely what effects each reagent produces in a homogeneous mixture. Hitherto far too little attention has been paid to the chemical and the physical aspects of cell-investigation ; substances capable of acting as
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