Experimental morphology / by Charles Benedict Davenport.

  • Davenport, Charles Benedict, 1866-1944.
Date:
1897-1899
Catalogue details

Licence: Public Domain Mark

Credit: Experimental morphology / by Charles Benedict Davenport. Source: Wellcome Collection.

    20/302 (page 2)
    certain indirect means for determining its constitution. Since death is due to chemical change, we ought to determine what substances are fatal poisons to protoplasm ; and since every activity of protoplasm is a chemical process, we ought to study the modifications of these processes by the action of various chemical reagents. In studying the behavior of protoplasm in the presence of various reagents, we shall make use especially of observa- tions upon Protista, sexual cells, and tissue cells. In cases where sufficient observations on isolated plant or animal cells are wanting, use will be made of observations upon Metazoa. At the outset, attention should be called to the necessity of a more quantitative study of the subject. A quantitative study demands, especially, a careful noting of the conditions of the experiment; for the various physical conditions under which the reagent is applied modify the result. Thus, it has been shown, for example, by Richet (’89, p. 212) that with various poisons the toxic dose diminishes in amount with the elevation of the temperature of the body. 1. Oxygen. — It is almost certain that no protoplasm can long survive in the absence of oxygen. Apparent exceptions are found in the case of the anaerobic bacteria, some of which are killed in the presence of free oxygen, but multiply rapidly when the oxygen supply is cut off. It has been suggested that, in the case of these and some other parasitic organisms, oxygen is derived from the breaking down of O -containing compounds in the nutritive medium. (Cf. Loew, ’91, p. 760.) The effect of diminished oxygen upon protoplasm is described by Clark (’89, pp. 870, 371) and by Demoor (’94, p. 191). Clark determined the minimum oxygen pressure necessary for the vital movements of the plasmodia of Myxomycetes and the protoplasm of plant hairs and tissue cells. This he found to range from 1 mm. (plasmodia of Myxomycetes) to 3 mm. (leaf hairs of Urtica) of mercury. Demoor* subjected Tradescantia stamen hairs, in water, to a * In studying the effect of a vacuum, Demoor employed a piece of apparatus constructed essentially on the plan of an Engelmann’s chamber. This consists of a box whose top is a centrally perforated metallic diaphragm and whose bottom is a circular glass. The vertical walls consist of an outer cylinder, at