AMORPHOUS CONTRACTILE SUBSTANCE. 437 



descriptive anatomical account of the passive and active or- 

 gans of locomotion ; and special treatises on anatomy almost 

 invariably give the uses and actions, as well as the structure 

 and relations of these parts. 



Amorphous Contractile Substance. In some of the very 

 lowest orders of beings, in which hardly any thing but amor- 

 phous matter and a few granules can be recognized by the 

 microscope, certain movements of elongation and retraction 

 of their amorphous substance have been observed. In the 

 higher animals, similar movements have been noticed in cer- 

 tain of their structures, such as the leucocytes, the contents 

 of the ovum, epithelial cells, and connective-tissue cells. 

 These movements are generally simple changes in the form 

 of the cell, nucleus, or whatever it may be. They are sup- 

 posed to depend upon an organic principle called sarcode, or 

 protoplasm ; 1 but it is not known that such movements are 

 characteristic of any one definite proximate principle, nor is 

 it easy to determine their cause and their physiological im- 

 portance. In the anatomical elements of adult animals of 

 the higher classes, the sarcodic movements usually appear 

 slow and gradual, even when viewed with high magnifying 

 powers; but in some of the very lowest orders of* being, 

 where these movements serve as the means of progression, 

 they are more rapid. 



It does not seem possible, in the present condition of our 

 knowledge, to explain the nature and cause of the move- 

 ments of homogeneous contractile substance ; and it must 



J5 J 



be excessively difficult, if not impossible, to observe directly 

 the effects of different stimuli, in the manner in which we 

 study the movements of muscles. As far as we can judge, 



1 KUHXE, Untersuchungen uber das Protoplasma und die Contractilitat, Leipzig, 

 1864. In this very elaborate memoir almost all varieties of contraction are re- 

 ferred to the action of the single principle, protoplasm. The chief physiological 

 interest, however, is attached to this explanation of muscular contraction ; but 

 there are few writers of authority who accept the view that it is entirely due to 

 the presence of the so-called protoplasm. 



