36 THE CONNECTIVE TISSUES [CH. IV. 



Blood is also mesoblastic, and thus the two first characteristics of 

 a connective tissue are present. It does not fulfil the third condition 

 by contributing to the support of the body as part of the skeleton, 

 but it does so in another sense, and serves to support the body by 

 conveying nutriment to all parts. 



Areolar Tissue. 



This is a very typical connective tissue. It has a wide distribu- 

 tion, and constitutes the subcutaneous, subserous, and submucous 

 tissues. It forms sheaths (fasciae) for muscles, nerves, blood-vessels, 

 glands, and internal organs, binding them in position and penetra- 

 ting into their interior, supports and connects their individual parts. 



If one takes a little of the subcutaneous tissue from an animal, 

 and stretches it out on a glass slide, it appears to the naked eye like 

 a soft, fleecy network of fine white fibres, with here and there wider 

 fibres joining it. It is, moreover, elastic. 



But in order to make out its structure accurately, it is necessary 

 to examine the thinnest portions of the film with the microscope, and 



FIG. 49. Bundles of the white fibres of areolar tissue partly unravelled. (After Sharpey. 



the action of staining and other reagents may then be also studied. 

 By such means it is seen that this typical connective tissue consists 

 of four different kinds of material, or, as they may be termed, histo- 

 logical elements. They are : 



(a) Cells, or connective-tissue corpuscles, 



(b) A homogeneous matrix, ground substance, or intercellular 



material. 



(c) White fibres ) Th deposited in the matrix. 



(d) Yellow or elastic fibres j 



