36 H. HAYS BULLARD 



positive results with the true interstitial granules. The fat drop- 

 lets of muscle fibers are not easily rendered insoluble by the 

 action of chromic compounds. For the most part the droplets 

 are dissolved by the alcohol or xylol used in the paraffin process 

 even when the tissues have been treated with 10 per cent potas- 

 sium bichromate for several days at 37°C. It follows then that 

 the fat droplets in muscle fibers are not shown by the Weigert 

 or iron-hematoxylin methods as ordinarily employed. When 

 chrom-osmic fixatives are used, as in the methods of Altmann 

 and Benda, the droplets are sometimes blackened and rendered 

 insoluble, but usually they are still soluble. When, as rarely 

 happens, fat droplets are rendered insoluble by the bichromate- 

 osmic mixtures, and at the same time not blackened by osmic, 

 they may be stained by Benda's iron-alum Krystallviolett and 

 probably also by hematoxylin or iron-hematoxylin. Since the 

 investigations of Smith and Mair ('08, '10, '11), Aschoff ('09), 

 and of Faure-Fremiet, Mayer and Schaeffer ('10) have shown that 

 the phosphatid lipoids, com.binations of cholesterin and fatty 

 acids, as well as cerebroside, are rendered insoluble by the action 

 of potassium bichromate, we may conclude that the fat droplets 

 of muscle fibers do not, to any very considerable extent, consist 

 of these fats. Saturated neutral fa^ are not rendered insoluble 

 by the action of potassium bichromate and triolein is acted upon 

 only very slowly. The fat droplets of muscle fibers not being 

 readily acted upon by potassium bichromate, react as if they were 

 composed wholly or largely of neutral fat. 



8. Formalin fixation. Bell ('10) pointed out the fact that fat 

 droplets in muscle fibers and other tissues are frequently not 

 preserved by formalin fixation. Droplets of ordinary neutral 

 fat he states are not affected in their staining by formalin fixation, 

 but many faintly-refractive fat droplets, consisting wholly or in 

 part of lipoids, cannot be stained after formalin fixation. The 

 faintly-refractive droplets are either removed or rendered invisible 

 by fixation. He finds that the action of the formalin fixative in 

 one tissue may be unapprcciable for weeks and in another nearly 

 all the liposomes may be removed in a few minutes. He states 

 that the varying effect of the fixative is probably due to the vary- 



