CHAPTER IX. 



THE CONTRACTILE TISSUES. 



SECT. 1. INTRODUCTORY. 

 THE STRUCTURE OF THE CONTRACTILE TISSUES. 



The pro- WHILE Schwann and other observers, about the year 

 perties of 1835, were tracing the resemblances of vegetable "and 



Protoplasm. animal tissues, Dujardin 1 , a French naturalist, was 

 investigating in some of the lower animals a remarkable substance 

 to which he gave the name of sarcode. This substance is amor- 

 phous, gelatinous of various degrees of consistence, and elastic ; 

 and it always contains granules of greater or less fineness. It 

 occurs in fragments whose shape is indefinite and indeed variable. 

 It is capable of developing within its mass vacuoles or cavities filled 

 with a pellucid fluid, which afterwards close so perfectly that no 

 crack or scar betrays their former presence. But it is chiefly remark- 

 able for its power of extending portions of its surface, at will, into 

 processes which may or may not inosculate, and which again, at will, 

 are withdrawn into the general mass. To this property the name 

 contractility is given. In what manner the protrusion is effected it is 

 impossible to decide ; but it is easy to imagine that the normal form of 

 the contractile mass of sarcode is spherical and that contraction may 

 be exerted in any chord: in which case the corresponding segment 

 would be pressed out as a process (Hermann). The projection of 

 columns or processes is not the only movement exhibited by sarcode. 

 The granules imbedded in its mass may undergo gliding and dancing 

 movements resembling the mechanical Brownian movements which 

 are seen when very minute particles are suspended in a liquid. 

 In each case the granules are passive. In the case of the gliding 

 movements, which are well seen along the extended processes of 

 foraminifera, the agent is the contractile sarcode; but in the case 

 of the dancing movements the cause may be the same as that of 

 the Browniao movements referred to. It is true that they may 

 be seen in contractile tissues which are unquestionably alive; but 



1 Dujardin, "Recherches sur les organismes inferieurs." Ann. des Sciences naturelles^ 

 2nd Ser. (1835), Vol. iv. p. 343. 



