LIVING SUBSTANCE 115 



Many salts occur dissolved in water, and they are present in all 

 living substance. The compounds of chlorine appear to be espe- 

 cially important, as well as the carbonates, sulphates, and phosphates 

 of the alkalies and alkaline earths, particularly sodium chloride 

 (common salt), potassium chloride, ammonium chloride, and sodium, 

 potassium, magnesium, ammonium, and calcium carbonates, sul- 

 phates and phosphates. 



Finally, as regards gases, there occur in all living substance 

 oxygen and carbonic acid. When not in chemical combination, 

 they are usually absorbed in water, and rarely, as in many uni- 

 cellular organisms, e.g., Rhizopoda, in the form of bubbles of gas. 



The special inorganic constituents of cells comprise a great 

 variety of substances, but for present purposes it is unnecessary 

 to discuss them. It is remarkable that in certain cells even 

 free mineral acids appear, such as hydrochloric acid, which is 

 produced by certain cells of the gastric glands in vertebrates, and 

 sulphuric acid, which in many marine snails is secreted by the 

 cells of the salivary glands. 



e. The Distribution of Substances in Protoplasm and Nucleus 



Although during the last few years our knowledge of cell- 

 morphology has increased greatly, and microscopic investigation 

 of the cell has revealed its finest structural relations, comparatively 

 little is known of the chemical nature of its individual morpho- 

 logical constituents. Here is the point where physiological micro- 

 chemistry must institute its work. The combination of microscopic 

 observation and chemical reaction alone is able to bridge the gap 

 between that which has become known morphologically as ground- 

 substance and solid constituents in the protoplasm and the nucleus, 

 and that which gross chemical analysis has shown to be the 

 constituents of living substance. The building of the bridge be- 

 tween the morphology and the chemistry of the cell is a difficult 

 undertaking, since the majority of reactions that can be employed 

 conveniently and easily in the test-tube, under the microscope on 

 account of the minuteness of the objects either give very indistinct 

 results, or are entire failures. Hence, first of all, delicate and re- 

 liable micro-chemical methods need to be devised. The first steps in 

 this direction have already been taken, and we have begun to obtain 

 here and there an insight into the distribution of the chemically 

 known substances within the cell-contents. 



It has been shown that the bodies that have been found as 

 morphological differentiations in the cell- contents, differ also 

 chemically. Especially the investigations of Miescher, Schwarz, 

 Zacharias, Altmann, Kossel, Lowitt, Malfatti and others have 

 proved that characteristic chemical differences exist between the 



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