i ORGANISATION AND STRUCTURE OF MUSCLE 7 



assumed that the sheath of the pedicle was the contractile organ. 

 The behaviour of Vorticellse, whose filaments have been totally or 

 partially destroyed, affords the clearest proof in favour of the first 

 view. With total destruction the power of contraction is entirely 

 abolished, with partial destruction the loss is in proportion with 

 the injury. 



The reaction of dead stalks is interesting in this connection. 

 They are invariably contracted (rigor mortis), and all reagents 

 that kill the filaments by coagulation (heat included) produce 

 a coiling up that lasts as long as the filaments are present. 

 When they are destroyed by decomposition, or by reagents, the 

 stalk lengthens again. These experiments show that the elonga- 

 tion depends upon the elasticity of the pedicular sheath. Engel- 

 mann (I.e. p. 438 f.) observed in Zootharnnium arbuscula that the 

 fibrils of the stalk-muscle, which in this case are quite visible, 

 become short, thick, and straight at the moment of contraction. 

 When relaxation begins, they lengthen again quickly, so that if 

 the sheath of the stalk is obstructed by any accidental, external 

 obstacle, and thus gets slowly longer, the fibrils at first present 

 a very sinuous appearance. The stalk - filaments of Vorticella 

 therefore consist undoubtedly of contractile fibrils. These observa- 

 tions (independently of other facts to be discussed later) seem 

 to disprove the conjecture of Kiihne (6) that it is not the filament 

 itself, but the sheath of the filament which he compares with 

 what he calls the "glia" element of muscle -cells in higher 

 animals that is contractile, the filament (i.e. fibrils) being on the 

 contrary an elastic tissue that produces extension in conjunction 

 with the sheath of the pedicle. 



Assuming the filament of the stalk to be the contractile ele- 

 ment, it is easy to explain the spiral coiling and uncoiling of the 

 latter, as was first indicated by Czermak. The stalk of the Con- 

 tractilia is a cylinder with a thin, elastic wall, to the inner 

 surface of which is attached a contractile filament descending in 

 a steep spiral. But when a cylinder contracts along a spiral 

 line upon its surface, it also becomes spiral. 



Up to the present time there have been few attempts at 

 artificial excitation of the stalk-muscle of Vorticella. Kiihne (7) 

 observed that Vorticella -colonies contracted suddenly when 

 tetanised with an induction current. All the stalks remain con- 

 tracted during stimulation, and it is only when the current passes 



