30 THE HUMAN BODY. 



them has any very marked physiological property; they are? 

 not, for example, irritable or contractile, and their mass is- 

 chiefly made up of an intercellular substance which has 

 been formed by the actively living cells sparsely scattered 

 through them, as for instance in cartilage, Fig. 42,* where 

 the cells are seen imbedded in cavities in a matrix which 

 they have formed around them; and which matrix by its 

 firmness and elasticity forms the functionally important 

 part of the tissue. 



3. Nutritive Tissues. This is a large group, the mem- 

 bers of which fall into three main divisions, viz. : 



Assimilative tissues, concerned in receiving and prepar- 

 ing food materials, and including (a) Secretory tissues, 

 composed of cells which make the digestive liquids poured 

 into alimentary canal, and bringing about chemical or other 

 changes in the food, (b) Receptive tissues, represented 

 by cells which line parts of the alimentary canal and take- 

 up the digested food. 



Eliminative or excretory tissues, represented by cells 

 in the kidneys, skin, and elsewhere, whose main business 

 it is to get rid of the waste products of the various parts of 

 the Body. 



Respiratory tissues. These are concerned in the gas- 

 eous interchanges between the Body and the surrounding 

 air. They are constituted by the cells lining the lungs. 

 and by the colored corpuscles of the blood. 



As regards the nutritive tissues it requires especially to be 

 borne in mind that although such a classification as is here 

 given is useful, as helping to show the method pursued in 

 the domestic economy of the Body, it is only imperfect 

 and largely artificial. Every cell of the Body is in itself 

 assimilative, respiratory, and excretory, and the tissues 

 in this class are only those concerned in the first and 

 last interchanges of material between it and the external 

 world. They provide or get rid of substances for the 

 whole Body, leaving the feeding and breathing and excre- 

 tion of its individual tissues to be ultimately looked after 

 by themselves, just as even the mandarin described by Eobin- 

 son Crusoe who found his dignity promoted by having 



