CONNECTIVE TISSM. 53 



of the cells themselves. At first this is homogeneous, but in 

 further development formed elements appear in the form of 

 fibres. After certain changes in the cellular elements and the 

 ground substance a form is reached which belongs to one of the 

 three main groups of connective tissues described above. 



In the spaces of the intercellular substance there lie various 

 kinds of cells, whose function it is to nourish the intercellular 

 substance. The nutritive fluids pass through the ground sub- 

 stance from one cell to another ; and when the ground substance 

 is of firm consistency there are special paths or canals formed. 



1. Connective Tissue. 



To this group belong those tissues whose intercellular sub- 

 stance (also called ground substance) is not especially firm, and 

 contains mucin, collagen, or elastin. We may distinguish sev- 

 eral kinds 



(a) Embryonic connective tissue. 



(b) Areolar or fibrillar tissue : 



(1) Intercellular substance : 



(a) White connective-tissue fibrils ; 

 (/?) Elastic fibrils ; 

 (/) Ground substance. 



(2) Cells: 



(a) Fixed cells ; 

 (/?) Granular cells ; 

 (/) Wandering cells. 

 (<?) White fibrous tissue. 



(d) Yellow elastic tissue. 



(e) Beticulum. 

 (/) Fat tissue. 



(a) Embryonic connective tissue (gelatinous tissue, mucoid 

 tissue) consists of round or stellate cells which are joined by 

 processes, between which there is a large quantity of mucus- 

 (mucin-) holding interstitial substance (Fig. 27). Mucin may 

 be recognized by treatment with acetic acid, with which it forms 

 a granular precipitate. In young embryos the intercellular 

 substance is homogeneous, while in older embryos connective- 



