I 



The Interstitial Granules of Striated Muscle etc. 299 



from the contractile substance, being more difficultly soluble in caustic 

 alkali and more readily soluble in acetic acid than the latter. Boiling in 

 5 to 10 per cent potassium hydroxide for some time dissolves the gran- 

 ules. In cold acetic acid, dilute or strong, they are visible for several 

 days as threads between the fibrillae. In water, alcohol, or ether the 

 granules are not dissolved by long boiling, with the exception of the dark 

 fat-like forms which disappear in ether at least. The interstitial granules 

 are of very general distribution. In mammals they are delicate and pale 

 and are best seen when they are fatty. The granules seem to arise by a 

 direct degeneration of the fibrillae, which is however a part of the normal 

 metabolism of the fiber. Kölliker admits that the considerable resis- 

 tance of the granules to chemical agents is against this view that they 

 are destructive products of the muscle substance, but nevertheless 

 accepts this as the most probable explanation. 



Krause [1873] states that the interstitial granules lie mainly in the 

 isotropic band, or are at least most readily visible there. In some in- 

 stances (especially flies in winter and "Maikäfer" in June) they are very 

 numerous and become arranged in a row oin either side of Krause's mem- 

 brane, forming the "Nebenscheiben". The granules are resistent to 

 alkalies and acids and blacken with osmic acid. Thefare destructive 

 products of muscle "metabolism. 



Knoll (1880 — 1881). describes the interstitial granules in the heart 

 muscle of pigeons. When examined in normal salt solution the 

 muscle fibers are seen to be full of droplets, some of which are 

 weakly-refractive and some strongly -refractive. After treatment of 

 the tissue with dilute acetic acid or sodium hydroxid, the weakly- 

 refractive droplets are harder to see but the others are not affect- 

 ed. Practically all the granules disappear after treatment of the 

 tissue two days in absolute alcohol and one day in ether. The 

 strongly-refractive droplets are true fat droplets; the weakly-refrac- 

 tive droplets are Kölliker's interstitial granules. The latter are 

 different from the true fat droplets but stand in genetic conti- 

 nuity with them. The weakly-refractive droplets give a weak 

 color with osmic acid and may be composed of lecithin. 



Kölliker [1888] describes the interstitial granules in the wing 



