METHODS OF PHYSIOLOGICAL RESEARCH 51 



unbounded field for cell -physiological investigation is revealed. The 

 comparative method demonstrates one fact of fundamental impor- 

 tance, namely, that the elementary vital phenomena belong to 

 every cell, whether it be from a tissue of the higher animals, the 

 lower animals, the plants, or free-living, an independent 

 unicellular organism. Every one of these cells exhibits in its 

 individual form general vital phenomena. Kealising this, it is 

 only necessary for the investigator to select from the variety of 

 species the objects best fitted for each special research, and these 

 obtrude themselves upon him in due form, if he possesses some 

 knowledge of the animal and plant world. It is no longer neces- 

 sary for him to cling to the tissue-cells of the higher vertebrates 

 alone, which can be employed for microscopic experiments alive 

 and under normal vital conditions only in rare and exceptional 

 cases, and which, as soon as they are separated from the tissue, are 

 under abnormal conditions and rapidly die or give reactions that 

 may lead to false conclusions. Much more favourable in this respect 

 are the tissue-cells of many invertebrates, cold-blooded animals, or 

 plants, which can be investigated more readily under approxi- 

 mately normal conditions, although frequently they also do not 

 endure long-continued study. But the free-living unicellular 

 organisms, the Protista, appear to be the most favourable objects 

 for cell-physiological purposes. They seem to have been created 

 by nature for the physiologists, for, besides their great capacity of 

 resistance, of all living things they have the invaluable advantage 

 of standing nearest to the first and simplest forms of life ; hence 

 they show in the simplest and most primitive form many vital 

 phenomena that by special adaptation have developed to great 

 complexity in the cells of the cell-community. 



Naturally it has been maintained that exactly the reverse is 

 true, that those forms of cells that are adapted to very special 

 functions in the cell-community of higher animals afford far more 

 favourable objects for the investigation of the phenomena in 

 question than unicellulai' organisms. Thus, it has been urged that 

 the cross-striated muscle-cell is decidedly more fitted for the 

 investigation of contraction than the amoeba-cell, because in the 

 latter all the phenomena of life are not separated, but are united 

 with the same substratum. However logical this assertion may 

 appear at first sight, upon careful consideration it proves to be 

 little applicable. In the first place, it is a great error to 

 assume that the various phenomena of life are inseparably united 

 in one cell in unicellular organisms alone. This is equally true 

 of every tissue-cell, whether it is adapted to a specific purpose 

 or exhibits prominently to external observation a single vital 

 phenomenon. Every cell, wherever it is, performs all the ele- 

 mentary functions of life. Without being nourished, without 

 respiring, and without excreting, the muscle-cell can execute its 



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