92 MANUAL OF PHYSIOLOGY. 



ding. Torulse, however, like bacteria, though called vegetables, 

 have not the power of assimilating as ordinary green plants do, 

 but require nutriment to be supplied to them which already con- 

 tains organic or complex compounds. Structurally but little 

 different from torula is a one-celled plant, the green protococcus, 

 which, like a higher plant, can build up its texture from the sim- 

 plest food stuffs, and carry on its functions. It consists of a case 

 made of cellulose, within which lies a mass of protoplasm with 

 a nucleus. The protoplasm is commonly colored green by a 

 peculiar substance called chlorophyll. We shall see presently 

 that it is to protoplasm containing chlorophyll, that plants owe 

 all their most characteristic and wonderful properties, viz., the 

 property of assimilating so as to construct complex carbon com- 

 pounds out of simple inorganic materials. 



The smallest and simplest organisms classed as animals are 

 generally larger than the vegetable cells just alluded to. They 

 consist of protoplasm without any nucleus, and only sometimes 

 with a structural difference between any part of their substance. 

 As an example we may take Protamceba. This is a small mass 

 of protoplasm without any nucleus, but its outer layer is clearer 

 and less granular than the central part. It can move by send- 

 ing out protoplasmic processes, in which currents can be observed 

 resembling those of the vegetable cells. Except as regards the 

 nucleus, it is much the same as the Amoeba, which can be more 

 readily watched, and will therefore be more accurately described. 



The amoeba is a single cell or mass of uncovered protoplasm, 

 containing a well-defined portion of substance or nucleus, within 

 which is a small speck or nucleolus. The central part of the 

 protoplasm is densely packed with coarse granules, but the outer, 

 more active part is structureless and translucent looking, some- 

 what like a fine border of muffed glass, incasing the coarsely gran- 

 ular middle portion. Such a one-celled animal has no special 

 parts differentiated for special purposes, the requirements of its 

 functions being so small that the protoplasm itself can accom- 

 plish them all. 



Thus the processes of protoplasm, which flow out with consid- 

 erable rapidity from the body, commonly encircle particles of 



