CH. VIII.] RHYTHMICAL1TY 101 



the higher animals (man included) execute the greater number of their 

 movements. 



If we contrast together amoeboid, ciliary, and muscular movement, 

 we find that they differ from each other very considerably. Amoeboid 

 movement can occur in any part of an amoeboid cell, and in any 

 direction. Ciliary and muscular movement are limited to one direc- 

 tion ; but they are all essentially similar, consisting of the movement 

 of hyaloplasm in and out of spongioplasm ; it is the arrangement of 

 the spongioplasm that limits and controls the movement of the hyalo- 

 plasm (see also p. 84). 



Rhythmicality. In some forms of movement there is not only 

 order in direction, but order in time also. This is seen in ciliary 

 movement, and in many involuntary forms of muscular tissue, such 

 as that of the heart. Here periods of contraction alternate with 

 periods of rest, and this occurs at regular intervals. Under the influ- 

 ence of certain saline solutions,* voluntary muscles may be made 

 artificially to exhibit rhythmic contractions. 



A familiar instance of rhythmic movement in the inorganic world 

 is seen in a water-tap nearly turned off but dripping ; water accumu- 

 lates at the mouth of the tap till the drop is big enough to fall ; it 

 falls, and the process is repeated. If, instead of water, gum or 

 treacle, or some other viscous substance is watched under similar 

 circumstances, the drops fall much more slowly ; each drop has to get 

 bigger before it possesses enough energy to fall. Thus we may get 

 different degrees or rates of rhythmic movement. So in the body, 

 during the period of rest, the cilium or the heart is accumulating 

 potential energy, till, as it were, it becomes so charged that it dis- 

 charges ; potential energy is converted into kinetic energy or move- 

 ment. 



When contraction travels as a wave along muscular fibres, or from 

 one muscular fibre to another, the term peristalsis is employed. 

 These waves are well seen in such a muscular tube as the intestine, 

 and are instrumental in moving its contents along. The heart's con- 

 traction is a similar but more complicated peristalsis occurring in a 

 rhythmic manner. 



Muscle and nerve are admirable tissues for studying irritability 

 and contractility. 



The question may be first asked, what evidence there is of irrita- 

 bility in muscle ? May not the irritability be a property of the 

 nerve-fibres which are distributed throughout the muscle and ter- 

 minate in its fibres ? The doctrine of independent muscular irrita- 



* Biedermann's fluid has the following composition : Sodium chloride 5 

 grammes, alkaline sodium phosphate 2 gr., sodium carbonate 0'5 gr. , water 1 litre. 

 If one end of the sartorius of a curarised frog is dipped into this fluid, it contracts 

 rhythmically in a manner analogous to the heart. 



