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MANUAL OF PHYSIOLOGY. 



say, it can feel. We can only judge of the sensitiveness of any 

 creature by the manner in which it responds to stimuli, and \ve 

 may, therefore, conclude that the smallest particle of living pro- 

 toplasm is endowed with definite sensitiveness; this must be 

 noted as one of the most striking properties of protoplasm. 



Every particle of living protoplasm has the power of assimila- 

 tion. Taking into its structure any nutrient matters it meets with, 

 by flowing around them in the way mentioned, it brings them 

 into direct contact with different parts of the protoplasmic sub- 

 stance. This nutrition of the form units gives rise to growth, and 

 finally leads to their reproduction, and these facts will be more 

 closely examined when speaking of their relation to cell life. 



FIG. 37. 



FIG. 36. 



FIG. 36. Cells of the yeast plant in processor budding, bet ween which are some bacteria 

 FIG. 37. Cartilage from young animal, showing the division of the cells (a, 6, c, d). 



When a certain size has been attained, the cell does not in- 

 crease any more, but tends to bring forth a cell unit similar to 

 itself. This is spoken of as the reproduction of cells. 



Different kinds of cell reproduction have been observed, which 

 are all, however, modifications of the same general plan. The 

 first is that by the formation of a bud from the side of the parent 

 cell ; this bud then increases in size, and finally separates from 

 the parent and becomes a separate individual. This process, 

 which is called gemmation, can readily be seen in all its stages in 

 growing yeast, where the torula cells have various sized buds 

 growing from them. If the bud-like protrusion be large, nearly 



