GENERAL HISTOLOGY 87 



SUMM.\RY OF HISTOLOGICAL FACTS. 



Cells. — I. The most important morphological element of all tissues 

 is the cell. 



2. The cell is a mass of protoplasm which contains one or several 

 nuclei (uninucleated, multinucleated cells). 



3. The nucleus probably determines the specific character of the cell, 

 since it influences its functions ; accordingly it is also the bearer of heredity. 



4. Cells and nuclei increase exclusively by division or budding, the 

 cells of the Metazoa nearly always by mitosis, those of the Protozoa 

 frequently by direct division. 



Tissues. — 5. Tissues are complexes of numerous similar histologically 

 differentiated cells. 



6. Histclogical differentiation rests in part upon the fact that the cells 

 assume a definite form and arrangement, in part upon the formation of 

 plasmic products, which determine the character of the tissue (muscle-, 

 nerve- and connective-tissue fibrils). 



Classification of Tissues. — 7. According to function and structure 

 (i) epithelia, (2) connective tissue, (3) muscular tissue, (4) nervous tissue 

 are distinguished. 



8. The physiological character of epithelia is due to the fact that they 

 cover the surfaces of the body; morphologically they consist of closely 

 appressed cells united by a cementing substance. 



9. According to their further functional character epithelia are divided 

 into glandular epithelia (unicellular and multicellular glands), sensory, 

 germinal, and protective epithelia. 



10. According to the structure are distinguished simple (cubical, 

 cylindrical, squamous epithelia) and stratified epithelia, ciliated and 

 flagellated epithelia, epithelia with or without cuticle. 



11. The physiological characteristic of the connective tissues is that 

 they fill spaces between other tissues in the body. 



12. The morphological distinction depends upon the presence of the 

 intercellular substance. 



13. According to the quantity and the structure of the intercellular 

 substance the connective tissues are divided into (i) cellular (scanty 

 intercellular substance); (2) homogeneous; (3) fibrous connective tissue; 

 (4) cartilage; (5) bone. 



14. The physiological character of muscular tissue is its increased 

 capacity for contraction. 



15. The morphological characteristic is the fact that the cells have 

 secreted muscle-substance. 



