l6o HOW TO WORK 



Revelations," by the same author, and papers in the Microscopical 

 Journal. 



25G. Contractility of Muscle. -- The actual movement taking 

 place in the particles of this tissue may be demonstrated in certain 

 of the lower animals, in which it continues for some time after the 

 tissue has been removed from the body. Muscular contraction may 

 be studied in small insects or Crustacea. Mr. Bowman strongly 

 recommends the muscular fibres from a young crab (Phil. Trans. 

 1841). Many small transparent aquatic larvae are also very favourable 

 for this purpose. 



The phenomena of muscular contractility may be most success- 

 fully studied in the broad muscles just beneath the skin of the 

 common maggot or larva of the blow-fly, and as these can be always 

 readily obtained, I recommend them for observation. The move- 

 ments, which are very beautiful, continue for ten minutes or a quarter 

 of an hour after the muscles have been removed from the body of the 

 recently killed animal, so that a specimen may be prepared and 

 passed round the lecture room in one of the portable microscopes, 

 p. 14. In the winter I have seen the contractions continue for 

 upwards of half an hour. It is most instructive to examine these 

 muscles during contraction under the influence of polarised light, 

 with a plate of selenite. When the ground is green, the waves of 

 contraction which pass along each muscular fibre in various direc- 

 tions, are of a bright purple. In other parts of the field the comple- 

 mentary colours are reversed. There are few microscopic objects, 

 that I am acquainted with, so beautiful as this. With the aid of very 

 high powers, the actual change occurring in the contractile tissue as 

 it passes from a state of relaxation to contraction, and from this to 

 relaxation again, may be studied, and for many minutes at a time. 



In order to obtain the muscles, it is only necessary to slit up the 

 larva, and after removing the viscera, to separate some of the muscles 

 from the outer skin to which they are attached. They may be mois- 

 tened with some white of egg, saliva, or better than all, a little of the 

 colourless fluid from the animal. 



In this way the student will form a good idea of the nature of 

 contradile movement generally, in which there is repetition. Contrac- 

 tility has been confused with movement essentially different in its 

 nature, which takes place in germinal or living matter, p. 170. The 

 first affects various kinds of formed material only ; the last is peculiar 

 to germinal matter. Contractility is essentially interrupted. Vital 

 movement is continuous. By the last, a weight may be raised higher 

 and higher, and if the weight increases the force which raises it may 

 increase also. Contraction involves yielding or relaxation. It is, as 



