38 H. HAYS BULLARD 



The action of formalin on the fat droplets is not what we should 

 expect if the droplets were an albumino-lipoid as suggested by 

 Bell. In fresh unfixed muscle fibers the droplets readily coalesce 

 to form larger globules. In formalin fixed material the coales- 

 cence i^ not so apparent, for the substance immediately surround- 

 ing each droplet has been coagulated. However by the examina- 

 tion of carefully teased muscle fibers it is easy to convince oneself 

 that the droplets themselves are not hardened but may still 

 coalesce. If albumin were present to any considerable extent, 

 the droplets would be fixed and no coalescence would take place. 

 Faure-Fremiet and his collaborators have shown that albumino- 

 lipoids are coagulated by formalin in such a manner as to render 

 the fatty substance almost insoluble in fat solvents. The fat 

 droplets of formalin fixed muscle fibers are apparently as easily 

 dissolved by alcohol as in fresh tissue. 



9. Summary. The fat droplets of muscle fibers are not largely 

 composed of fatty acids or soaps for they do not stain by the 

 methods of Benda, Fischler and Klotz. They are not fatty acids 

 for they do not stain readily with basic anilin dyes. The fat 

 droplets do not contain cholesterin esters to a very considerable 

 extent for they do not present the characteristic anisotropic 

 fluid-crystalline form. The droplets are not phosphatid lipoids 

 or cerebroside for these substances are easily rendered insoluble 

 by potassium bichromate, whereas the fat droplets of muscle 

 fibers are not rendered insoluble. Also phosphatid lipoids and 

 cerebroside stain with basic dyes, giving blue with Nile blue, while 

 the fat droplets of muscle, at least for the most part, stain red 

 with this dye and are colored blue only after a chemical change 

 has occurred in the fat. Fat droplets in muscle fibers are readily 

 stained by alkaline-alcoholic solutions of Scharlach R and Sudan 

 III but are frequently left unstained by simple alcoholic solutions 

 of these dyes. The evidence which tends to show that the fat 

 droplets of muscle fibers are neutral fat (glycerin esters of fatty 

 acids) is largely of a negative character. It is improbable that 

 they are pure neutral fat, yet it may be said that no certain proof 

 has yet been offered that any substance other than neutral fat 

 is present in the fat droplets of muscle fibers during the life of 

 the animal. 



