234 Dr. Beale Croonian Lecture. [May 11, 



and which are intended to show the alterations in form supposed to take 

 place in the ultimate particles of any contractile tissue movements occurring 

 in definite directions, which may be represented by lines at right angles to 

 one another. These movements are quite distinct from those varied move- 

 ments in all directions which affect matter in the germinal or living state. 

 Contractile tissue is formed material, and contractility occurs in tissue 

 which does not exhibit any of those properties or powers which distinguish 

 living matter. It seems to me, therefore, that contractility is not a vital 

 property; and I think that the term contractility should be restricted to 

 movements which are remarkable for their constant repetition, and for the 

 simplicity of their character. The changes which occur in the particles of 

 a muscle during action might be spoken of as alternate shortening and 

 lengthening. 



Experiment. 



The phenomena of contractility can be studied more satisfactorily in the 

 muscles of the common maggot or larva of the blow-fly than in those of 

 any other animal I am acquainted with. The movements, which are very 

 beautiful, continue for ten minutes or a quarter of an hour after the muscles 

 have been removed from the body of the recently killed animal; and I hope 

 to be able to prepare a specimen which can be passed round in one of the 

 portable microscopes and examined by the Fellows. [Preparation sent 

 round.] In the winter I have seen the contractions continue for upwards 

 of half an hour. But the most beautiful and instructive method of exa- 

 mination is under the influence of polarized light, with a plate of selenite. 

 In the microscope upon the table, the arrangement has been made; and 

 when the ground is green, the waves of contraction which pass along each 

 muscular fibre in various directions, are of a bright purple. In other parts 

 of the field the complementary colours are reversed. There are few micro- 

 scopic objects, that I am acquainted with, so beautiful as this. With the aid 

 of very high powers, the actual change occurring in the contractile tissue as 

 it passes from a state of relaxation to contraction, and from this to relaxa- 

 tion again, may be studied, and for many minutes at a time*. 



Molecular movements. The cause of the so-called molecular movements 

 is probably complex, but quite independent upon any phenomena peculiar 

 to living beings. 



The various movements occurring in the ultimate elementary parts or 

 " cells " of living beings may be arranged as follows : 



1. Primary or vital movements. Affecting matter in the living state 

 only and occurring in every direction, as seen in the amoeba, white blood- 

 corpuscle, mucus- and pus-corpuscle, young cells of epithelium, and in 

 germinal matter generally. 



* The character of muscular movements is fully described in Mr. Bowman's well- 

 'known paper (Phil. Trans. 1841). See also Mr. Bowman's article, " Muscular Motion," 

 in Todd's Cyclopaedia of Anatomy and Physiology. 



