CHAP. IX ] THE CONTRACTILE TISSUES. 319 



axis-cylinder divides in Mammals, Birds and Reptiles, into a 

 short dendriform structure called an End-plate, which rests upon a 

 granular nucleated mass called a Protoplasmic foot. In Amphibia, 

 there is no protoplasmic foot, and the divisions of the axis- 

 cylinder are nucleated and long, extending mainly in the long axis 

 of the fibre, immediately beneath the sarcolemma. In all classes 

 the white substance of Schwann terminates somewhat abruptly at 

 the entrance to the sarcolemma or at a little distance within it 1 . 

 In muscular fibres destitute of sarcolemma the nerve ends in a 

 granular Eminence of Doy&re 2 , on the side of the fibres which usually 

 bears a nucleus. 



CHEMICAL CONSTITUTION OF NORMAL LIVING MUSCLE, so FAR 



AS IT CAN BE KNOWN OR INFERRED. 



On the distribution of liquid and solid parts in a voluntary muscular 



fibre. 



In the section which has preceded, an account has been given of 

 the appearances presented by muscular fibres when subjected to a 

 high magnifying power; and we have shewn that, according to 

 all observers, there is contained within the elastic sarcolemma a 

 substance in which doubly refracting and isotropous structures 

 alternate. In the sequel it will be shewn that in the process of con- 

 traction the fibre becomes shorter and thicker, and that at the same 

 time the anisotropous elements become broader and shorter, the inter- 

 mediate isotropous substance also exhibiting some diminution in 

 height and perhaps (though this admits of doubt) diminishing in 

 amount. Whilst these changes in the form are proceeding, differences 

 in light- transmitting powers are perceived, though the behaviour to 

 polarized light remains as before. 



We have referred to minor points in which different observers 

 disagree, but without laying very much stress upon them. We have 

 now, however, to discuss a question which is of paramount importance, 

 in reference to the physical constitution of voluntary muscle. 



When we examine a dead muscular fibre, especially one which has 

 been acted upon by various hardening reagents, the contents of the 

 sarcolemma all unquestionably possess a solid consistence. Can 

 we, however, infer from such observations that they possess the same 

 characters during life ? Certainly not. It was shewn by Kiihne 3 that 



1 Kiihne, Strieker's Handbuch, chap. v. 



2 Doyere, "MSmoire sur les Tardigrades. " Ann. des Sci. Nat., Ser. n. Vol. xrv., 

 1840, p. 269. 



3 Kiihne, ArcMv f. Anat. u. Physiol, 1859, p. 748. Untersuchungen uber das 

 Protoplasma und uber die Contractilitdt. Leipzig, 1864. (Consult section entitled 

 "Methoden zur Gewinnung des Muskelinhalts, " p. 2.) Lehrbuch der physiologischen 

 Chemie, Leipzig, 1866, p. 272. 



