312 E. T. Bell, 



literature. Kölliker, in 1857, made a distinction between "true" intersti- 

 tial granules and fat droplets. He stated that the true interstitial gran- 

 ules are corpuscles peculiar to muscle and distinct from fat droplets, 

 but expressed the view that the fat droplets are derived from the intersti- 

 tial granules by metamorphosis. This apparently has been the pre- 

 vailing belief since Kölliker's publication. Knoll however stated that 

 the strongly-refractive granules consist entirely of neutral fat, and that 

 the weakly-refractive granules have a peripheral layer of neutral fat 

 and a central core probably composed of lecithin. Some years later 

 Albrecht came to the conclusion that the granules are composed of 

 lipoid substances. Among those who have regarded the interstitial 

 granules as distinct from fat droplets may be mentioned Retzius, 

 Ballowitz, Prenant, Heidenhain, Holmgren, and Knoche. Prenant 

 apparently behoves that the granules are composed of a chemical 

 substance preparatory to fat. Undoubtedly much of the disagreement 

 in regard to the composition of the interstitial granules is due to the 

 fact that observers have been dealing with different structures. The 

 large Q-granules of insect muscle are not liposomes. In my judgment 

 the fuchsinophile granules of Altmann are not liposomes. Some of 

 Arnold's plasmosomes and Retzius' sarcosomes may be liposomes, but 

 the majority of them are not. Knoll, Albrecht and Kölliker (1857) 

 were dealing with liposomes. Holmgren, Knoche, and Kölliker (1888) 

 were discussing the large Q-granules of insect muscle. 



Several methods have been employed to determine the composition 

 of the granules: the study of a) their appearance in fresh tissues, 

 b) their solubility, c) their behavior toward histological fixatives and 

 stains, d) their behavior during inanition, e) the effect of special 

 feeding on the granules. The evidence from each of these sources will 

 be considered separately. 



a) The appearance of the interstitial granules in fresh tissue. It 

 has been known for a long time that droplets of ordinary neutral fat 

 are strongly-refractive when examined in the fresh tissue. As a rule it 

 is conversely true that the strongly-refractive droplets to be seen in fresh 

 tissue are of a fatty composition, but of course solubility and staining 

 tests are necessary for a certain identification. Some tests were made 



