16 



INTRODUCTION 



shaped in the older tissue cells. They are composed of phospho- 

 lipids and protein in varying proportions, and are soluble in fat 

 solvents, but can be preserved by formalin and potassium dichro- 

 mate. Janus green reacts with them in the living cell, and their 

 activities may be readily followed after staining with this dye. 

 Various observers have associated them with the formation of fat, 

 of fibrils, and of secretion granules. They move about in the 

 cytoplasm, grow and divide, and transform from the granular to 

 the rod or filamentous forms (or lylce versa) in the living cell. 



Secretion 

 granules 



Golgi bodies- 



es ^-^••••••.•^•♦••. 



Nuclear membrune- 

 Nucleolus- 



Chromatin- 



Cytoplasm- 



K^^il 



'ell membrane 



■Vacuole 



■Mitochondria 

 (chrondriosomes) 



-Central body 



Fig. 1. — Diagram of a typical cell. 



The apparatus of Golgi, a reticular structure often close to the 

 nucleus, was first demonstrated in certain nerve cells. These bodies 

 are formed of lipoids, which are fixed with osmium tetroxide, or 

 they may be dissolved with fat solvents, leaving empty canaliculi 

 in their place. Their function is unknown, but their occurrence 

 is so general that they are considered normal intracellular structures, 

 concerned in some unknown manner with cell function. They 

 apparently vary in composition with different states of the cell. 



Close to the nucleus there is to be found another structure of 

 almost universal occurrence in animal cells, the central a])])aratus, 

 or centrosome. In the resting cell it is inconsi)icnous, but becomes 

 prominent during mitotic (indirect) division of the cell. During 



