S2 LIVING MATTER OR PROTOPLASM. 



ously as to be nearly or quite invisible until the movements are 

 in some way made sluggish. The movement is then seen to be 

 more rapid and vigorous in one direction than in the other, all the 

 cilia working together like the oars of a row-boat. By this action 

 a definite current is produced in the surrounding medium (in this 

 case the mucus of the trachea) flowing in the direction of the 

 more vigorous movement. In the trachea this movement is up- 

 wards towards the mouth, and mucus, dust, etc., are thus removed 

 from the lungs and windpipe. In many lower animals and plants, 

 especially in the embryonic state, cilia are used as organs of loco- 

 motion, serving as oars to drive the organism through the water. 

 The male reproductive germs of plants and animals are also pro- 

 pelled in a similar fashion. 



Actions like those just described are known as automatic. 

 They take place without evident cause and do not answer to any 

 discoverable external stimulus. Automaticity in this sense is a 

 property of all protoplasm ; for it appears under numberless 

 forms of which movement is only one example. Another 

 general property of protoplasm which has been well illustrated 

 by the phenomena just described is known as contractility. The 

 swaying of the strands of protoplasm of Tradescantia, the short- 

 ening of the muscle-fibre, the waves in the protoplasmic current 

 of Nitella, the protrusion of the pseudopods in Amoeba, and 

 the bending of the cilia in the windpipe are all due to this in- 

 trinsic property of living matter. 



These examples of visible vital actions have been chosen to 

 help the student to a better conception of the invisible phenom- 

 ena which underlie them. There can be no doubt that within 

 the substance of a living gland-cell or brain-cell there is a play 

 of invisible molecular actions far more tumultuous and compli- 

 cated than the visible movements displayed in Nltella or a nettle- 

 hair; and it is of the utmost importance that the student should 

 attain to a full and vivid sense of the reality and energy of this 

 invisible activity even in protoplasm which under the closest 

 scrutiny appears to be absolutely quiescent. 



Energy. Whence comes the power expended in protoplasmic 

 action ? The power to do work, or energy, is required for every 

 action ; and according to the doctrine of the conservation of 

 energy it is never generated de novo, but only transformed or 



