52 GENERAL PHYSIOLOGY 



movements no more than can the amoeba. There is no cell 

 whatever that plays one role alone, for it is inherent in the nature 

 of the vital process to exhibit different phases. Hence it is quite 

 wrong to regard the inauguration of the act of contraction in the 

 muscle-cell as something simpler than that in the amoeba. But 

 further, microscopic study teaches that contraction in the cross- 

 striated muscle-cell is associated with a substratum morpho- 

 logically much more complex than that in the amoeba. The 

 differentiation of various kinds of elements in the former, regard- 

 ing the significance of which we have scarcely any idea, is very 

 astonishing in comparison with the naked amoeba with its single 

 cell-body. Moreover, the history of research has shown satis- 

 factorily that in spite of the overwhelming amount of labour 

 that has been employed for centuries upon the investigation of 

 contractile phenomena in muscle, up to the present time we have 

 hardly gone beyond conjecture of the most general kind in the 

 solution of the problem. Hence we are not only justified in 

 employing, but even compelled to employ the simpler forms of 

 contractile substance as an important research-object in the 

 investigation of the problem of contraction, and an analogous 

 requirement is demanded for the investigation of other problems, 

 It is obvious that in the study of an elementary vital phenomenon, 

 even among unicellular organisms, objects must always be chosen in 

 which the phenomenon is exhibited sufficiently clearly. For the 

 investigation of secretion cells must be chosen in which the act of 

 secretion is readily accessible ; just as in the study of contraction 

 only those in which contractile movements are directly visible. 

 Further, it will be necessary to treat the vital phenomena in the 

 various kinds of cells comparatively, for comparative cell-physiology 

 alone is able to separate the special and unessential from the 

 general and essential. Hence it would be a mistake to neglect 

 the tissue-cells while studying unicellular organisms. Not rarely 

 opportunities are offered where for one consideration or another 

 the tissue-cells or whole masses of tissue of plants or animals are 

 to be preferred ; where, indeed, as in many special problems of 

 physiology, the tissue-cell becomes the real object of investigation. 

 It would not be in place here to present a one-sided or schematic 

 view, or to lay down general rules. In every individual case the 

 choice of object is to be determined solely by the problem. One 

 thing only should always be kept in view, namely, the investi- 

 gation of the life of the cell. 



Morphology, the forerunner of all physiology, has smoothed the 

 way for physiological research. We know to-day the structure of 

 cells in minute detail, whether they are free-living or united 

 into tissues, and we are indebted directly to histological research 

 for much important information and many valuable sugges- 

 tions respecting the vital phenomena, especially of tissue-cells, 



