GENERAL ANATOMY. 73 



all the vital phenomena, such as movement, sensation, 

 assimilation, previously ascribed to many organs. Du- 

 jardin's theory was stoutly contested by Ehrenberg and 

 his school, but finally attained general acceptance through 

 the pioneer work of Max Schultze and Haeckel. 



Schultze's Protoplasm Theory. On the basis of 

 the three above-mentioned series of observations, Max 

 Schultze finally established the above briefly sketched ref- 

 ormation of the cell theory, when through an exact study 

 of the appearance and the vital phenomena, and by means 

 of numerous experiments, he proved that the cell-substance 

 of animals, the sarcode of protozoa, and the protoplasm 

 of plants are identical, and that to this substance, for 

 which he retained the name protoplasm, all the vital 

 phenomena of animals and plants are referable in the 

 ultimate analysis. The second important reform concerns 

 the changes of cells into tissues. These follow not so much 

 through changes of form and modification of the cells into 

 the tissue elements, as Schwann thought, but rather by 

 means of chemical changes. By means of its formative 

 potentiality the protoplasm gives rise to non-protoplasmic 

 structural parts, as, for example, connective-tissue fibrils, 

 muscle fibrils, nerve fibres, etc., but which nevertheless 

 make up the specific character of the various tissues, and 

 perform the functions of these, and also in addition retain 

 as the source of life and formation the unemployed rem- 

 nants of cells, the connective-tissue corpuscles, muscle 

 corpuscles, etc. We will now trace out farther these two 

 fundamental ideas in Max Schultze's " protoplasm theory," 

 and thereby briefly sketch the foundation of the modern 

 theory of tissues. 



Nature of the Cell. The size of the animal cell 

 varies to a considerable degree ; the smallest elements are 

 the male sexual cells, the spermatozoa, whose bodies, par- 

 ticularly in case of the mammals, are even less than 

 0.005 mm. ; the largest, on the other hand, with the excep- 

 tion of the giant plasmodia of some mycetozoa, are the 

 egg cells. The yellow portion of the bird's egg, which 



