PERISTALTIC MOTION. 99 



striated muscle-fibres. But, as we know, this is not a 

 distinction of kind, but only one of degree; for we 

 found that in the case of striated muscle also there is 

 a stage of latent irritation, then a gradually increas- 

 ing, and then again a gradually decreasing contraction. 

 But that which in striated muscle occupies but a few 

 parts of a second, in smooth muscle-fibres occupies a 

 period of several seconds. JSTo artificial aid is, there- 

 fore, required in this case to distinguish the separate 

 stages. At present, research into the nature of smooth 

 muscle-fibre has not resulted in the acquirement of more 

 than this somewhat superficial knowledge. Owing espe- 

 cially to the difficulty of isolating the fibres, and to the 

 rapidity with which they lose their irritability when 

 separated from the body, it is very difficult to experi- 

 ment with them. It is especially not yet clear by what 

 means the transference of the irritation arising at one 

 point to the other part is effected. The transference 

 never occurs in the case of striated muscle. If a long, 

 thin, parallel-fibred muscle is separated out on a glass 

 plate, and a very small part of it is then irritated, the 

 irritation immediately propagates itself in a longitudiiial 

 direction in the muscle-fibre immediately touched. It 

 is impossible to produce contraction in a striated muscle- 

 fibre only at one point in its length, at least while the 

 muscle-fibre is fresh. In dying muscle-fibres such local 

 contractions do indeed occur. Each separate muscle- 

 fibre, therefore, forms a closed whole in which the con- 

 traction excited, at one point spreads over the whole 

 fibre. The speed with which it spreads within the 

 fibre has even been measured. As the striated muscle- 

 fibre in contracting becomes also thicker, a small light 

 lever, if attached to the fibre, is somewhat raised, 



