448 MOVEMENTS. 



out the nuclei more strongly. If we have an indistinct 

 sheet of this tissue in the field of view, the addition of acetic 

 acid, by bringing out the long, narrow, and curved nuclei 

 arranged in regular order, and rendering the fibrous and 

 other structures more transparent, will often enable us to 

 recognize its character. 



Contraction of the Involuntary Muscular Tissue. The 

 mode of contraction of the involuntary muscles is peculiar. 

 It does not take place immediately upon the reception of a 

 stimulus, applied either directly or through the nerves, but 

 is gradual, enduring for a time and then followed by slow 

 and gradual relaxation. A description of the peristaltic 

 movements of the intestines gives a perfect idea of the mode 

 of contraction of these fibres, with the gradual propagation 

 of the stimulus along the alimentary canal, as the food makes 

 its impression upon the mucous membrane. 1 An equally 

 striking illustration is afforded by labor-pains. These are 

 due to the muscular contractions of the uterus, and last 

 from a few seconds to one or two minutes. 3 Their gradual 

 access, continuation for a certain period, and gradual disap- 

 pearance coincide exactly with the history of the contrac- 

 tions of the involuntary muscular fibres. 



The strong points of contrast between the mode of 

 action of the striated and the smooth muscular fibres are 

 very well brought out in a recent paper by MM. Legros and 

 Onimus. These observers, after carefully studying the 

 structure and properties of the " muscles of vegetative life," 

 give, in substance, the following resume of their physio- 

 logical action : 



The contraction is slow, and the fibres return slowly to a 

 condition of repose. The movements are always involun- 

 tary. Peristaltic action is the rule ; and the contraction 

 takes place progressively and without oscillations. Con- 



1 See vol. ii., Digestion, p. 376, et seq. 



2 CAZEAUX, A Theoretical and Practical Treatise on Midwifery, Philadelphia, 

 1857, p. 123. 



