HUMAN ANATOMY. 



during one stage of its existence as granular and at a later period as reticular, has 

 done much to bring into accord the conflicting and seemingly irreconcilable views 

 regarding the structure of the cell championed by competent authorities. 



Whatever be the particular phase of structural arrangement exhibited by the 

 cell, histologists are agreed that the cytoplasm consists of two substances, — an active 

 and 2i passive ; while both must be regarded as living, the vital manifestations of con- 

 tractility are produced by the former. 



Since a more or less pronounced reticular arrangement of the active and passive 

 constituents of cytoplasm is of wide occurrence in mature cells, this condition may 

 serve as the basis for the description of the morphology of the typical cell. 



Critical examination of many cells, especially the more highly differentiated 

 forms of glandular epithelium, shows the cytoplasm to contain a mesh-work com- 

 posed of delicate fibrils and septa of the more active substance, the spongioplasm ; 

 although conspicuous after appropriate staining, the spongioplastic net-work may be 

 seen in the unstained and living cell, thereby proving that such structural details are 

 not artefacts due to the action of reagents upon the albuminous substances com- 

 posing the protoplasm. 



The interstices of the mesh-work are filled with a clear homogeneous semifluid 

 material to which the name of hyaloplasm has been applied. Embedded within the 

 hyaloplasm, a variable amount of foreign substances is frequently present ; these 



A 



Fig. 6. 

 B 



C 



Spermatogenic cells, showing variations in the condition and the arrangement of the conbUluents of the cyto- 

 plasm and the'nucleus; the centrosomes are seen within the cytoplasm close to the nucleus. A, from the guinea-pig 

 X 1685 {Meves) ; B, from- the salamander X 500 {Meves) ; C, from the cat X 75° (.von Lenhossek). 



include particles of oil, pigment, secretory products, and other extraneous materials, 

 which, while possibly of importance in fulfilling the purposes of the cell, are not among 

 vis essential morphological constituents. These substances, which are inert and take 

 no part in the vital activity of the cell, are termed collectively metaplasvi. 



Cytoplasm consists, therefore, morphologically, of the spongioplasm and the 

 hyaloplasm ; chemically, cytoplasm consists of certain organic compounds, salts and 

 wi ter. The organic compounds are grouped under the term proteiyis, which are 

 complex combinations of carbon, hydrogen, nitrogen, and oxygen, with often a small 

 percentage of sulphur. The proteins of the cytoplasm contain little or no phosphorus. 



Structure of the Nucleus. — The nucleus, during the vegetative condition of 

 the cell, or the "resting stage," as often less accurately called, appears as a more 

 or less spherical body whose outline is sharply defined from the surrounding cyto- 

 plasm by a definite envelope, the nuclear membrane. Since the nucleus is the 

 nutritive, as well as reproductive, organ of the cell, the fact that this part of the cell 

 is relatively large in young and actively growing elements is readily explained. 



The nucleus consists of two parts, an irregular reticulum of nuclear fibres and 

 an intervening semifluid nuclear matrix, therein resembling the cytoplasm. Exam- 

 ined under high magnification, after appropriate treatment with particular stains, such 

 as hematoxylin, safranin, and other basic dyes, the nuclear fibres are shown to be 

 composed of minute irregular masses of a deeply colored substance, appropriately 



