OF THE GLOBULE OR CELL. 13 



begotten, but only possess characteristics distinctly physical, 

 such as elasticity, toughness, etc. However, there are some, 

 forming a separate class, which possess even in a higher 

 degree the properties characterized by the primitive globule, 

 as, for instance, the muscular fibre, which, in addition to 

 its elasticity, is endowed with an electro-motor as well as 

 even a still more essential property, that of changing its 

 form under the influence of excitants. The nerve fibre pos- 

 sesses properties not exactly similar to the above, but yet 

 highly characteristic of the condition of life. 



These are the principal phenomena presented by the gen- 

 eral review of cellular physiology. As before remarked, they 

 all occur under the influence of excitants or irritants. We 

 have shown how these may be divided into physical, chemi- 

 cal, or vital, this division being sufficiently accurate for the 

 physiologist, though the most diverse excitants may cause the 

 same effect; for example, a shock or simple touch brings 

 about cellular contraction, especially in the muscles; elec- 

 tricity, or certain acids even, produce the same phenomenon, 

 which is naturally, in the physiological condition, almost ex- 

 clusively manifested under the influence of the nervous sys- 

 tem. A more interesting division would be based upon the 

 nature, not the effects of the excitant. This, unfortunately, is 

 impossible. Yet, following out this plan, some have tried to 

 recognize three kinds of irritability : irritability of formation 

 or of development, trophic or nutrient irritability, and func- 

 tional irritability. We have, however, seen how the different 

 phenomena of development," nutrition, function, and even 

 death, form a physiological product that should artificially be 

 subdivided for convenience of study. 



Can the irritability of development be separated from that 

 of nutrition. Have we not also seen that cells, those of the 

 glands, for instance, perform their chief function by disap- 

 pearing as a cell element, and then becoming liquefied, appear 

 as a secretion? An attempt has been made to divide the 

 functions of the isolated globule as well as those of the entire 

 organism into three great classes, viz. : relation, reproduc- 

 tion, and nutrition, as if the functions of reproduction were 

 not concerned in either of the two other divisions. 



The theory that life resides in the excitable elements re- 

 acting differently with different excitations, is quite ancient, 

 and the history of the words excitant, excitability, and of 

 those synonymes which have turn by turn taken their place, 

 as, for instance, irritant, irritability, incitant, incitability, 



