154: THE AMEEICAN MONTHLY [July, 



exists. The protoplasm surrounds several globular bodies which are 

 found to contain diatoms and alga-spores and other living creatures 

 still minuter than amoeba ; these globules are called "'• food-vacuoles." 

 In addition to food-vacuoles amceba presents one vacuole which con- 

 tains no food, and which now and then shrinks up and disappears, to 

 later suddenly appear again. This is the " contracltle vacuole ." One 

 other part is present in amoeba but invisible in the living specimen ; it 

 is the nucleus. Briefly, then, amoeba is a minute drop irregular of out- 

 line of protoplasm which presents the following parts, viz : i. Food 

 vacuoles. 2. Contraclile vacuoles. 3. Nucleus. 



Amceba Physiology. — Since amoeba is protoplasm we may expect 

 some or all of the protoplasmic powers. What, then, can amoeba do.? 

 It can move. As you watch it under the microscope you observe a 

 flow among the granules which compose it. Movement results in a 

 circulation within the drop and change in the shape of the drop. The 

 substance flows toward one side and away from the other and the drop 

 thus moves from place to place. In this way amoeba glides about and 

 soon escapes from the field of observation unless followed. It can 

 metabolize ; this cannot be actually seen, for we cannot observe the 

 molecular structure no matter how well we are equipped with micro- 

 scopical appliances, but we can infer it, for amoeba's substance does not 

 waste away but rather increases in bulk, and oxygen is undoubtedly 

 used up and carbonic acid and ammonia given oft', though in too small 

 amounts to be easily detected. It can feel stimulation, and this we can 

 see, for if we make amoeba swim between the poles of an electric bat- 

 tery and then send a gentle current from pole to pole, amoeba shrinks 

 up into a ball, but presently resumes its motion until it feels a second 

 shock. Amoeba protoplasm thus can perform the various acts of pro- 

 toplasm. The constant activity of amoeba may at certain times cease, 

 and later be resumed, and we therefore say that amoeba is automatic 

 or self-controlling. All living things are thus self- directive. 



Other Cells and their Powers. — We shall have a better idea of 

 cells by briefly noticing a few other kinds and their powers. A cake 

 of compressed yeast consists of millions of cells mixed with grains of 

 starch. Single cells are oval in outline and are composed of a wall, 

 within which is the protoplasm not filling the cell, but leaving one or 

 more central spaces, " vacuoles," which are filled with water and dis- 

 solved chemical substances. If the yeast be thinned with a weak solu- 

 tion of sugar and set aside in a warm chamber for a few hours, it will 

 have produced a certain amount of carbonic acid gas which will give 

 a sour odor and a bubbly look to the fluid, and the cells will have pro- 

 duced buds or smaller cells, which may have in their turn pi'oduced still 

 other buds. Here, then, are cells which are actively producing chem- 

 ical changes or metabolisms, anabolizing sugar, and increasing the bulk 

 of protoplasm, and katabolizing, something which produces carbonic 

 acid, a very simple chemical compound. Yeast cells cannot go on very 

 long producing protoplasm and growing in bulk by budding, unless 

 they have a better diet than sugar and water. 



Plant hairs, as, for instance, the hairs on the stamens of the spider- 

 wort or many other plant hairs, are rows of oblong cells with a firm 

 boundary wall of cellulose and within a thin lining of protoplasm, which 

 lining is in communication with the centre where the nucleus lies by 



