Mr F. Cohn on the Contractile Filaments in Thistles. 193 
unwrinkled. The process of contraction may be followed 
directly under the microscope, since water, or glycerine, 
kills the cells sooner or later. The edges of the cells are 
seen to become wavy. After a little, the cross-striping is 
everywhere evident. Almost instantaneously the extreme 
contraction of the filament occurs, and at the same time 
the closest corrugation of its cells. 
Although unable to follow the action of a temporary sti- 
mulus under the microscope (since the filaments soaked in 
water to render them transparent do not again extend 
themselves), the author expresses his conviction that the 
momentary shortening of the filament by stimulus, equally 
with the permanent contraction in death, depends upon a 
transverse corrugation of the cells. The filaments in short- 
ening become thicker; the following are measurements of 
breadth before and after stimulation :— 
w ae 
Betore, see 5 After, ~5, 
106 my 119 wt 
” 1000 ad 1000 
116 we 127 a 
ae ie » «1000 
From the circumstance that contraction ensues upon 
death equally as upon a temporary stimulus, the author is 
induced to believe that the cells of the elongated filament 
are in a state of active expansion, while the contracted con- 
dition depends upon a relaxation, in consequence of which 
the elasticity to which the expansive force was opposed now 
comes into play. ‘This elasticity appears to reside chiefly in 
the very thick cuticula, which does not, even in the most 
contracted filament, exhibit any corrugation, thus showing 
itself to be highly elastic. 
The author believes that at least in the lowest animals 
(which possess, not muscles, but a contractile parenchyma) 
the same conditions hold as in contractile vegetable cells. 
In these animals occurs the same momentary contraction 
by stimulus, and the permanent and utmost contraction in 
death, apparently in consequence of the elasticity of their 
cuticula; whilst their elongation and extension is a vital 
and active process. For example, the stalks of the Vorti- 
_ cellas become rolled up equally upon stimulation as upon 
