xi THE ELEMENTS OF STRUCTURE 197 



microscope we find that these are composed of many 

 cells, which may be defined as unit-masses or unit-areas 

 of living matter each centred in a nucleus. 



Corresponding to this morphological analysis there is a 

 physiological analysis which does not concern us at pre- 

 sent. But the general parallelism should be noted. 

 Just as the morphologist begins with the form of the 

 whole animal, so the physiologist begins with the intact 

 animal as a unity with habits and temperaments. He 

 goes on to consider it as an engine made up of organs, 

 as an intricate fabric of tissues, as a city of cells, and as 

 a strangely unified whirlpool of living matter. 



With the school of Cuvier we associate the beginning 

 of a masterly comparative study of the organs of animals ; 

 and it is with the name of Bichat (whose Anatomic 

 Generate was published in 1801) that we associate the 

 first vigorous analysis of organs into tissues. If we take 



o 



the next step of analysis, and think of the body as a 

 complex city of cells, we are better able to understand 

 what tissues are. Each cell corresponds to a house, a 

 tissue corresponds to a street of similar houses. In some 

 cities we see homogeneous streets of similar shops, one 

 street devoted to bread-making, another to boot-making. 

 So in the animal body aggregates of contractile cells 

 form muscular tissue, of supporting cells skeletal tissue, 

 of secreting cells glandular tissue, and so on. 



It must suffice to state the general idea that a tissue 

 is an aggregate of more or less similar cells, and to note 

 that the different kinds may be grouped as follows :- 



I. Nervous tissue, consisting of cells which receive, 



transmit, or originate nerve-stimuli. 

 II. Muscular tissue, consisting of contractile cells. 



III. Epithelial tissue, consisting of lining and covering 



cells, which often become glandular, exuding 

 the products of their activity as secretions. 



IV. Connective tissue, including cells which bind, 



support, and store. 



Cells. To the discovery and perfecting of the micro- 

 scope we owe the analysis of the body into its unit masses 



