

CH. VIII.] KHYTHMICALITY 83 



tion ; but they arc 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. 68). 



Ehythmicality. 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 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 discharges; 

 potential energy is converted into kinetic energy or movement. 



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

 one 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 contraction is 

 a more complicated peristalsis occurring in a rhythmic manner. 



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- 

 bility was enunciated by Haller more than a century ago, and was 

 afterwards keenly debated. It was "finally settled by the following 

 experiment of Claude Bernard. 



If a frog is taken and its brain destroyed by pithing, it loses con- 

 sciousness, but the circulation goes on, and the tissues of its body 

 retain their vitality for a considerable time. If now a few drops of a 

 solution of curare, the South American arrow poison, are injected 

 with a small syringe under the skin of its back, it loses in a few minutes 

 all power of movement. If next the sciatic or any other nerve going 



* 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. A solution of pure sodium 

 chloride (0'65 per cent.) has a similar action. 



