HISTORY OF PHYSIOLOGY. 13 



it yet been thoroughly taken in every case, for there are 

 many organs, especially in backboneless animals, about whose 

 predominant use we are very uncertain. But the physiolog- 

 ists of this school sometimes finished their work too quickly. 

 That the liver was an organ for secreting bile was for a long 

 time deemed a completely satisfactory statement, until it 

 began to be seen that this organ is the seat of many other 

 activities. Moreover, some thought that it was possible to 

 deduce the function of an organ from the nature of its 

 structure, as one would infer the use of a piston from its 

 shape. To a certain extent we can explain the functions of 

 an organ in terms of its visible structure, as when we shew 

 how an image is formed on the retina of the eye. But we 

 cannot, in terms of visible structure, explain another function 

 of the eye — that of distinguishing the " colours " of things. 

 In short, it must be clearly understood that each organ is 

 far more than a piece of mechanism in a living engine, — " 

 that it is a compUcated factory of living units, each with 

 subtle and manifold powers. 



In 1 80 1, Bichat analysed the animal body into its 

 component tissues or living strands — muscular, nervous, 

 glandular, etc., and being a physiologist as well as an 

 anatomist, tried to explain the activities of the organism in 

 terms of the contractile, irritable, secretory, or other pro- 

 perties of its tissues. This was a further step in the analysis, 

 and one of great importance. 



About forty years later, however, it began to be recognised 

 that the body was a great city of cells, each with a lif? of its 

 own. The functions were not merely the activities of organs 

 of various construction, or of tissues with various properties, 

 they were the results of the life of the component units or 

 cells. 



Finally, in those last days the physiologists have touched 

 the bottom in their analysis, for they are striving with might 

 and main to discover the physical and chemical changes 

 associated with the living stuff or protoplasm itself. These 

 are obviously at the foundation of the whole matter. 



