24 THK NKUYorS SYSTEM AND ITS <( )\Si:i; \.\TK )\ 



which i- prominent in the limit majority i- the nucleus, 

 This is a body witliin the cell, seemingly more dense th:ui 

 tlie remainder and unlike the rest in its chemical character. 

 The last fact is proved by the individual reactions of the 

 nucleus toward selected stains or dyes. When tissues 

 are treated with such solutions, the nucleus, which may 

 have been quite invisible in the uncolored specimen, 

 appropriates the stain and stands out in striking contrast 

 to the pale Mibstance which envelops it. Exceptionally 

 there may be more than one nucleus to a cell or, attain, 

 none may be discernible, ('ells are said to be compo-ed 

 of in-nlo/ilii.-oH, and the word is often used as synonymous 

 with living matter. Huxley called it the /tlii/.^icul /;.s/x uf 

 lift . The particular word r///o/;/u.x/// will be found useful 

 to designate the portion of the cell which is external to 

 the nucleus. 



The statement that tissues are composed of cells is 

 open to some objection. Tissues are made by cells, but 

 in the course of their development they commonly come 

 to contain material of a sort which cannot be described 

 as cellular. Such material is conveniently termed 'inter- 

 cellular substance" and it is probably always lifeless. 

 Sometimes it is scarcelv recojiiii/able. while at the other 

 extreme it may be so abundant as to constitute the main 

 bulk of the tissue and to determine its physical properties 

 and its value to the animal. Thus, bone is serviceable 

 because of the intercellular lime salts which <i;ive it rigid- 

 ity. The cells have come to occupy a very inconspicuou- 

 po>ilion, and though they continue to exert a needed 

 influence upon nutrition, they are not at all concerned 

 from moment to moment in the mechanical function 

 fulfilled by the bone as a part of the skeleton. All con- 

 nective tissue is distinguished by the hi.nh proportion of 

 intercellular substance contained in it. The dear, u'lassy 

 concrete of cartilage, the toii^h, white fibers in tendons 

 and ligaments, the network between the skin and the 

 muscles these are example- of material which is not made 

 of cells, though it was made hi/ them. 



