106 BIOLOGICAL LECTURES. 



which occur during their discharge and the structures connected 

 therewith. It is evident that all this also has bearings upon 

 our conception of the purpose and meaning of the cell upon 

 the cell theory in general. This is not the place to deal with 

 the applications which I have made elsewhere of these facts 

 with reference to the cellular theory, and I will only state one 

 point which stands out clearly above the rest. 



The cell is a whole. It is an organism both irritable and 

 responsive, and in a way creative. Not only the germ cell, but 

 also the finally differentiated cell must be regarded as an entire 

 organism, which under certain stimuli is able to set free a 

 certain amount of energy and create new structures. The 

 structures themselves are not to be confounded with what we 

 call response to stimulus; they are only a side product during 

 the process of irritation and reaction. Thus the stimulus of a 

 foreign solid particle imbedded in the cytoplasm calls forth 

 the response of secretion. That this secretion assumes the 

 form of drops around the excretory granules is merely due to 

 the physical properties of fluids; this form or structure of 

 round drops is only an expression of the most suitable and 

 direct path along which the response follows the stimulus. 

 Another point which I must insist upon is that structures 

 always appear first where stimulus and protoplasm meet, there- 

 fore, near the surface of the cell. The intracellular musculature 

 around the central canal apparently lies in the interior of the 

 cell, but if we consider that the canal is filled with fluid it 

 becomes evident that, for the cytoplasm, the central canal is 

 as much exterior as the surrounding tissues; that the wall of 

 the canal is an inner surface of the cell. The cilia and the 

 peripheral organs appear on the surface of the cell. 



There is given, on the one hand, irritable protoplasm, on the 

 other hand, chemical and mechanical stimuli, and, behold! struc- 

 ture has followed naturally. This looks very nice, but we must 

 not overlook the fact that all this only means the surveying 

 and describing of the paths along which phenomena take place, 

 and not an insight into the nature of the phenomena them- 

 selves. The cause of life is the same as the one which makes 

 water get firm under a low temperature, and which makes salts 



