LIFE AND ENERGY 3 



shapes. Neglecting these for the present, we will examine the 

 clearest part of the protoplasm. The very clearest part of all will 

 be noticed when a part of the protoplasm makes a protrusion, 

 called a " pseudopodium," because it serves the purpose of a leg, 

 and causes the animal to move along. In this part it will be 

 difficult or impossible to see any structure at all, a fact which 

 shows that the visible grains and so forth are not essential con- 

 stituents of living material. 



The whole organism, protoplasm and nucleus, is known as a 

 " cell." The name does not seem very appropriate in this particular 

 case, but it was first applied to the constituent parts of vegetable 

 organisms, in which what corresponds to the whole amoeba is 

 enclosed in a box of material which is not itself living. Under 

 certain conditions, amoeba itself forms a coating around itself 

 and becomes quiescent. 



The larger and more familiar plants and animals are composed 

 of a great number of cells, joined together in a community for 

 mutual help. Some of them do one thing, some do other things ; 

 whereas, in the unicellular beings, the one cell performs all the 

 functions of which the organism is capable. This fact, of course, 

 .makes it practically impossible to discover much from observa- 

 tions on these creatures. But we can find out many of the 

 fundamental and necessary properties belonging to all living 

 cells. 



Apart from the fact that what we see in the moving protoplasm 

 of an amoeba conveys the unavoidable impression that it is liquid, 

 there are other facts which confirm this (p., p. 6). But before 

 we proceed to these facts, it should be pointed out that, so far as 

 can be made out, protoplasm sometimes sets into a jelly and ceases 

 to be liquid. This is a temporary state, and the liquid condition 

 returns again, as when an ordinary jelly is warmed (p., p. 19)4 

 In protoplasm, the change from one state to the other occurs* 

 without altering the temperature. This process will be better 

 understood after we have learned something about what is called 

 the " colloidal state." 



Brownian Movement and the Ultra-Microscope 



If we look at the smallest particles which we can see in proto- 

 plasm by the use of a fairly high magnification with the microscope, 

 we notice that they are in a perpetual kind of dancing movement. 

 This can also be seen with any small particles suspended in water. 

 The yellow resin, gamboge, used as a water colour, rubbed up in 

 water, shows it very well (E., p. 166). The name of the form of 



