26 GENERAL PHYSIOLOGY 



found in large amounts in sperm-cells, the eggs of fishes, nervous tissue, and the 

 yolk of eggs, and in small amounts in striated and cardiac muscle cells. Cere- 

 brosides, i.e., bodies, containing nitrogen but no phosphorus, are contained in 

 spermatozoa and leukocytes. Fatty acid and neutral fat, i.e., substances contain- 

 ing neither nitrogen nor phosphorus, are very common constituents of cells; the 

 nucleus, however, is said to be free from fat. Cholesterin, one of the substances 

 belonging to this group, is a primary constituent, but nothing definite regarding 

 its origin and condition is known. The lipoids facilitate the solubility of those 

 substances which are otherwise scarcely soluble in water. They also play a part 

 in hemolysis and absorption. 



The proteins are the most constant and important constituent of the cell.^ 

 They occur in the cytoplasm as well as in the nucleus and belong chiefly to the class 

 of the proteids. The nucleoproteids of the nucleus are to be sharply differentiated 

 from the proteins of the cytoplasm, because it has not been definitely settled as 

 yet whether these bodies are absolutely identical. " Nuclein " was first isolated by 

 Miescher^ from the nuclei of the pus-corpuscles. Somewhat later KosseP demon- 

 strated that the essential constituents of this body are the purin and pyrimidin sub- 

 stances and not the phosphorus. That this is true may be gathered from the 

 fact that the yolk of the unfertilized egg of birds contains no purin, while the 

 developing eggs yield large amounts of this substance. Somewhat later Altmann* 

 succeeded in abstracting nucleic acid from different proteids. This constituent 

 of the nucleoproteids seems to be present in rather constant quantities, while the 

 albuminous material appears to fluctuate considerably. It is usually combined 

 with a basic albuminous substance, forming such bodies as protamin or histon. 

 The isolation of these components of the nucleoproteid is easily effected in most 



Carbohydrates are not found as free primary constituents of the cell, but are 

 contained in the nucleic acid portion of the nucleoproteids, in glycoproteids and 

 cerebrosides. In the cells of the liver glycogen in held as a reserve foodstuff. 



Among the inorganic substances masked iron has been shown to exist in chro- 

 matin.^ Less convincing results have been obtained pertaining to phosphorus. 

 Protoplasm, however, contains many of the commonest salts, namely, sodium, 

 potassium, magnesium, calcium, iron (sulphates, chlorids, phosphates and carbon- 

 ates), and at times also iodin, manganese, copper, zinc, barium and silicon. The 

 proportion of these elements, however, differs in different cells; in fact, those named 

 last should be regarded merely as accidental admixtures, because they are present 

 only under special conditions. It should also be emphasized that these inorganic 

 substances may occur either independently or in combination with the organic 

 material; moreover, they should not be considered as passive constituents, because 

 they play an important part in the production of all vital phenomena. 



Water constitutes about three-fourths of living substance, the remaining portion 

 of it being composed of inorganic and organic material. In some instances, in fact, 

 as much as 94 per cent, of it consists of water and the common salts. For this 

 reason, it must be evident that the specific gravity of protoplasm must show con- 

 siderable variations, although it may be said that its average value is about 1.025. 

 This value, for example, holds true absolutely in the case of paramecia which 

 Jensen® subjected to different known concentrations of potassium carbonate 

 solutions. It is conceivable, however, that certain cells, and especially those 

 containing calcareous admixtures, exceed this value, while others, possessing 

 prominent vacuoles, may fall below unity and be buoyant. 



1 Kanitz, in Oppenheimer's Handb. der Biochemie, ii, 1910, 213. 



2 Histochem. und physiol. Arbeiten, ii, 3, Leipzig, 1900. 



3 Zeitschr. fiir physik. Chemie, x, 1866, 248. 

 * Archiv fur Anat. und Physiol., 1889, 524. 



6 A. B. Maccallum, Ergebnisse der Physiol., vii, 1908, 552. 



^Pfliiger's Archiv, liv, 1893, 537; also: Lillie, Journ. of Morphol., xii, 1896. 



