n CHANGE OF FORM IN MUSCLE DURING ACTIVITY 159 



Interference between two waves of contraction coining from 

 opposite sides (the two terminal sections of a fibre) was only 

 once observed by Ilollett, when the two waves at first united 

 into one larger wave and then expired. 



The " fixed " waves of contraction, described above, are due 

 (as appears probable from liollett, 19) to a kind of summation ; 

 they may frequently be observed in the muscle-fibres of insects 

 killed in alcohol and osmic acid. They are usually distinguished 

 from the waves of living muscle by their yrcater length, which 

 Engelmann explains on the supposition that they were fixed 

 while their rapidity of transmission was still considerable. 



Eollett, however, assumes that " an entire series of short, 

 consecutive, living waves were partially fixed in succession, so that 

 they do not represent any single process, but are the sum of 

 fixed parts of contraction waves in time order. If any given 

 point of the muscle-fibre has for some time been the starting- 

 point of short periodic waves, some of the contracted muscle 

 sections will frequently, as Eollett says, remain fixed, while the 

 adjacent muscle -sections on either side relax again. Thus a 

 persistent contraction is produced in a short segment of the 

 muscle only, and from this the remaining waves spread outwards. 

 And it must be observed that each new wave that originates 

 from the contracted section, itself gives rise to one similar section, 

 while the rest relax again ; in this way the area of fixed con- 

 traction grows longer and longer, till at last the whole movement 

 is blocked, or ceases with a wave that dies out against the relaxed 

 end of the fibre." Such fixed waves can rarely be demonstrated 



/ 



on the muscles of vertebrates, in which waves of contraction may 

 of course be seen, but not the lively, persistent, spontaneous 

 undulation (Bowman, I.e.; Nasse, 21). Dover's expansion is very 

 commonly the starting-point of undulation in insect muscle, and 

 accordingly, the spot at which fixed waves of contraction are 

 readily formed. Sometimes partial contraction is exhibited, the 

 so-called lateral waves (f>n<l>'x /<tfr,'<t/es) of fixed contraction. 

 Rollett assigns this as a special characteristic of most Chry- 

 somelid (V, p. 216) muscle-fibres, while in other insect muscles 

 lateral waves of contraction occur rarely (Tenebrionidcr, Cur- 

 culionidce, and Scarabceidce). The nerve-ending of the Chrysome- 

 licles seems to present a special point of departure for a physio- 

 logical reaction which occurs with 1 ( osmic acid, and alcohol, or 



