FAT AND MITOCHONDRIA IN CARDIAC MUSCLE 25 



to occur in skeletal muscle and have been described in cardiac 

 muscle by Holmgren ('10), Regaud ('09) and Prenant ('11). In 

 most investigations concerning the structure and physiology of 

 muscle, particularly of cardiac muscle, these granules are ignored. 

 At the present time we possess little definite knowledge of their 

 chemical nature and still less of their physiological significance. 

 According to Regaud ('09) they are mitochondria and chemically 

 an albuminolipoid compound or mixture. 



The true interstitial granules are by no means identical with 

 the structures which I have described as neutral fat droplets. 

 The properties both chemical and morphological of each type 

 mark it off sharply from the other and I have not been able to 

 observe any transitional forms. 



True interstitial granules appear to be composed of a rather 

 soft plastic substance which easily takes the form imposed by 

 surrounding structures. They are seen as threads, rodules, 

 flattened plates, dumbbell shaped bodies, diplosomes, ovoids and 

 rarely as spheres. In cardiac muscle these granules are usually 

 limited to segment Q and this with great precision, figure 15. 



In order to determine the chemical nature of the true inter- 

 stitial granules I have made a study of numerous preparations 

 both fresh, fixed, stained and unstained. As regards refractive 

 index the granules differ but little from the myo-fibrillae. It is 

 therefore difficult, although at times not impossible, to observe 

 them in fresh unstained tissue. I have not determined with 

 certainty whether they are singly or doubly refractive but it 

 is certain that they are not typical doubly refractive fluid crystals 

 of cholesterin ester. In fresh preparations mounted in water one 

 can observe that the granules give rise to forms identical with 

 or closely resembling myelin figures which stain with cresyl violet 

 and at times with neutral red. With Scharlach R. the granules 

 stain but faintly or not at all. In fresh unfixed tissue they are 

 easily stained b^- dilute aqueous solutions of cresyl violet (Krause 

 '11) but after treatment with absolute alcohol or other fat solvents 

 the}^ no longer take the stain. They are readily stained by the so- 

 called mitochondrial methods but when the tissues are placed in 

 absolute alcohol before being chromated the granules appear as 



