THE FUNDAMENTAL PHYSIOLOGICAL ACTIONS. 17 



tion with the thinking, and so on. By such subsidiary ar- 

 rangements the working of the whole Body becomes so com- 

 plex that it would fill many pages merely to enumerate what 

 is known of the duties of its various parts. However, all the 

 proper physiological properties depend in ultimate analysis 

 on a small number of faculties which are possessed by all 

 living things, their great variety in the human Body depend- 

 ing upon special development and combination in different 

 tissues and organs; and before attempting to study them in, 

 their most complex forms it is advantageous to 

 examine them in their simplest and most gen- 

 eralized manifestations, as exhibited by some of 

 the lowest living things or by the simplest con- 

 stituents of our own Bodies. 



Cells. Among the anatomical elements 

 which the histologist meets with as entering into 

 the composition of the human Body are minute 

 granular masses of a soft consistence, about 

 0.012 millimeter (-g^Vcr ^ an i ncn ) i n diameter 

 (Fig. 5, b). Imbedded in each lies a central 

 portion, not so granular and therefore different 

 in appearance from the rest. These anatomical 

 units are known as cells, the granular substance Fio.5. Forms 

 being the cell-body and the imbedded clearer por- g f |j el ' s from the 

 tion the cell-nucleus,. Inside the nucleus may 

 often be distinguished a still smaller body the nucleolus. 

 Cells of this kind exist in abundance in the blood, where they 

 are known as the white blood-corpuscles, and each exhibits of 

 itself certain properties which are distinctive of all living 

 things as compared with inanimate objects. 



Cell Growth. In the first place, each such cell can take 

 up materials from its outside and build them up into its own 

 peculiar substance; and this does not occur by the deposit of 

 new layers of material like its own on the surface of the cell 

 (as a crystal might increase in an evaporating solution of the 

 same salt), but in an entirely different way. The cell takes 

 up chemical elements, either free or combined in a manner 

 different from that in which they exist in its own living sub- 

 stance, and works chemical changes in them by which they 

 are made into part and parcel of itself. Moreover, the new 

 material thus formed is not deposited, at any rate necessarily 

 or always, on the surface of the old, but is laid down in the 



