The Interstitial Granules of Striated Muscle etc. 313 



with a few fats to study the appearance of the droplets in aqueous 

 solutions. Thin smears of ordinary connective tissue fat, olive oil, 

 lecithin, and oleic acid were examined in water. The droplets in every 

 case show a wide range in size but all of them, however small, are strongly- 

 refractive. 



The refractive index of the interstitial granules, however, varies 

 greatly. Some are strongly-refractive; others are faintly refractive. 

 All possible intermediate forms between the two extremes are often to 

 be seen. In vertebrate muscle large granules are nearly always strongly- 

 refractive, and as a rule the smaller granules are less refractive. But 

 the refractive power does not depend merely upon size, since many 

 small granules are strongly-refractive. 



The above tests with fat smears would lead us to expect that the 

 strongly-refractive droplets in the tissues consist entirely of fats, and 

 all the tests (to be given later) bear out this view ; but the study of the 

 fat smears also shows that the faintly refractive droplets in the tissues 

 do not consist entirely of ordinary neutral fat, oleic acid, or lecithin, 

 since all the droplets of these substances are strongly-refractive. 



Some evidence will be presented later to support the view that 

 the refractive power of a granule depends upon the percentage of fat it 

 contains. According to this view the same kind of fat may be present in 

 both kinds of granules, but there is relatively less in those that are less 

 refractive. 



All the liposomes except those that are very faintly-refractive 

 may be seen when the fresh muscle is examined in aqueous humor or 

 the tissue juices^). The study of the fresh tissue shows us that these 

 interstitial granules are not artefacts, and suggests their fatty nature. 

 The differences in refractive power point to differences in chemical 

 composition. 



b) Solubility. Kolliker (1857) found that the solubility of the 

 interstitial granules of frog muscle was not very different from that of 

 the contractile substance. He states that the granules are somewhat 

 more difficultly soluble in caustic alkali and more readily soluble in 



^) The fuchsinophile granules shown by Altmann in vertebrate muscle are not 

 visible in the fresh tissue. 



