TISSUES OF THE BODY. 



291 



166. 



The occurrence in its substance of certain foreign molecules, partly con- 

 sisting of fat, is another peculiarity of the muscle fibre. These are known 

 as the " interstitial granules of Koelliker" although described long ago 

 by Henle. 



They are not always distinct in human muscle, but when present are 

 encountered in rows parallel to the direction of the fleshy fibres. 



In the muscle of the frog they appear with greater distinctness (rig. 

 284, d), and are often uncommonly numerous also, resisting, further, the 



Fig. 284. 



Fig. 285. Muscle fibre from the leg of a 

 frog, after prolonged treatment with 

 dilute hydrochloric acid. From the 

 cut surface very fine fibres are seen 

 projecting, a; with granules, b; the 

 latter are distributed along the whole 

 fibre. 



action of water acidulated with hydrochloric acid entirely. Here they 

 commence at the poles of the nuclei, and appear as though situated in a 

 system of canal-like interstices, occupied by nuclei, granules, and fat 

 molecules (Koelliker), which, under ordinary circumstances, are filled up 

 with the well-known protoplasm. When coagulated, these masses may 

 form a series of extremely delicate fibres (0*0006 mm. thick) and project from 

 the cut end of a muscle fibre which has been treated with water contain- 

 ing a trace of hydrochloric acid (fig. 285). The fibres contain fat mole- 

 cules, partly externally, and partly in the interior. Leydig, JBottcher, and 0. 

 Weber, erroneously regard these structures, together with the nuclei of the 

 muscle, as a network of stellate connective-tissue cells with tubular pro- 

 cesses traversing the substance of the muscle-fibres. 



On transverse sections of muscles which have been dried and subse- 

 quently moistened (fig. 286, a), we see these rows of fat granules as 

 a number of dark dots, as long as the molecules remain in the section, 



