214 STUDYING THE CONTRACTION OF MUSCULAR TISSUE. 



in front of, another particle. A contractile tissue 

 might be likened to a chain of beads, every bead 

 being capable of becoming short and broad or long 

 and narrow, but forced to retain, by reason of its 

 connexions, its relative position with regard to every 

 other bead. But the particles of a mass of living 

 matter are not thus chained together. Each is free to 

 move in any direction whatever, and the particles do 

 not retain the same relative position for a moment. 

 The movements of the muscular tissue, as regards 

 direction, extent, and place, are limited, and are 

 determined by external forces. The contractile cord 

 may become shorter, causing its points of attachment 

 to approximate, but it cannot move itself in its 

 entirety. On the other hand, it is characteristic of 

 living matter to move in any direction, and to pass 

 from one place to another, according to the operation 

 of forces acting from within the matter itself. 



There is, therefore, no analogy between the move- 

 ments of hving bioplasm and those of contractile 

 tissues formed from living bioplasm. These move- 

 ments are essentially diiferent from one another, and 

 cannot be classed together. Moreover, living matter 

 takes up pabulum, and changes this or some of its 

 constituents into living matter like itself, but under 

 no circumstances, actual or conceivable, qan the con- 

 tractile tissue produce more contractile tissue like itself. 



259. Of studying the contraction of lunscular 

 tissue. — The phenomena of conti-actihty can be 

 studied more satisfactorily in the muscles of the 

 common maggot or larva of the blow-fly than in 

 those of any otlier animal I am acquainted with. The 

 movements, which are very beautiful in these par- 

 ticular muscles, continue even in hot weather for ten 

 minutes or a quarter of an hour after the muscles 

 have been removed fi'om the body of the recently 

 killed animal. A specimen may be prepared and 

 passed round the lecture-room. In the winter I have 



