8 ELECTRO-PHYSIOLOGY CHAP. 



for a prolonged period that the' filaments begin to expand again 

 during tetanisation ; the animals then contract only slightly from 

 time to time, although if the current is strengthened, they can 

 still shrink up to the junction with the bell. Headless stalks, 

 when isolated, react in the same manner. Chemical stimuli 

 (HC1 1 %, NH 3 ) also cause the stalks of Vorticella to con- 

 tract (Kiihne, I.e. p. 828). With a dilute solution of vera- 

 trin the stalks draw together slowly, and become intensely 

 rigid, while the inner muscular filaments grow more highly 

 refractive, and therefore much more visible. A very dilute 

 solution of strychnia is equally fatal to Vorticella, but the pheno- 

 mena are different. The animals lose their excitability, and 

 remain passively extended, although there is a continuous ciliary 

 movement. In this state the strongest induction shocks, as well 

 as strong solutions of curare, fail to produce any movement 

 (Kiihne, I.e.) 



The propagation of excitability in the muscle of the stalk 

 should also be more exactly studied. There can be no doubt 

 that under normal conditions spontaneous excitation, as well as 

 contraction caused by external stimuli, spreads from the body of 

 the vorticella. The excessive rapidity of contraction in the muscle- 

 filament makes it indeed impossible to detect where the process 

 begins, as it is apparently initiated everywhere at the same 

 moment. This is the case even in the branched colonies of 

 Zoothamnium, or Carchesium, when the whole community is 

 retracted on mechanically exciting one individual. In Zootham- 

 nium there may be direct conductivity of excitation, since every 

 individual is a conductor to the rest through the muscular layer 

 of its pedicle ; but in Carchesium, where this is not the case, the 

 convulsion communicated from one contracting individual to the 

 next appears to be the only stimulus (Verworn, 4). In order 

 to explain the phenomena of contraction, not merely in Vorti- 

 cella, but in all other myoid Ciliata, it is necessary to assume 

 that excitation can be conveyed from every point of the body- 

 plasma to the muscle -fibrils, which are, collectively, in juxta- 

 position or direct connection with it ; and the rate at which 

 the excitation is propagated must be very considerable, under 

 all conditions far exceeding that of the Ehizopoda. For if 

 a .spirostomuin, or stentor, which from their elongated form are 

 next to vorticella the best suited to such experiments, be 



