SECOND LECTURE. 



CLASSIFICATION OF THE TISSUES. — BLOOD, LYMPH, CHYLE. 



A CLASSIFICATION of the tissues was, in the course of time, 

 often attempted ; but it is, and remains, a very difficult thing. 

 A scientifically adequate arrangement can be founded only 

 on the course of development of the elements. The latter is 

 unfortunately not yet accurately established throughout. 

 One might nevertheless proceed with strictness, by the aid of 

 the history of development ; the three well-known germinal 

 plates from which the embryo arises might be employed as a 

 basis of the arrangement. Still the representation of the tis- 

 sues thus arranged would be attended with not inconsiderable 

 difficulties. 



We will, therefore, employ a preponderating artificial 

 classification, which, with all its defectiveness, possesses, at 

 least, the advantage of presenting the material in a more 

 convenient form to the learner. 



We distinguish : 



A. Tissues of simple cells with fluid intermediate sub- 

 stance : I. Blood; 2. Lymph; 3. Chyle. 



B. Tissues of simple cells with scanty, firm, structureless 

 intermediate substance : 4. Epithelium; 5. Nails; 6. Hair. 



C. Tissues of simple or metamorphosed cells, with partly 

 still homogeneous, partly fibrous, and, not rarely, more firm 

 intermediate substances (connective-tissue group) : 7- Carti- 

 lage ; 8. Gelatinous tissue and reticular connective substance ; 

 9. Fat tissue; 10. Connective tissue; 11. Bone tissue; 12. 

 Dentinal tissue. 



D. Tissues of metamorphosed, as a rule, unfused, cells, with 

 scanty structureless intermediate substance: 13. Enamel tis- 

 sue ; 14. Lens tissue ; 15. Muscular tissue. 



