GRANULES AND FAT OF STRIATED MUSCLE 37 



ing chemical composition of the liposomes. Bell also found that 

 usually the fat droplets in the muscle fibers of adult and well 

 nourished animals are less affected by formalin than are the drop- 

 lets of young and poorly nourished animals. However, many 

 exceptions to this rule were mentioned. Bell ('11) confirms his 

 former observations and states further that the faintly-refractive 

 liposomes, which are removed by formalin fixation, consist in 

 part of a substance other than fat, possibly an albumino-lipoid. 

 He believes that the disappearance of the liposomes is probably 

 due to autolysis. 



I have repeatedly observed the gradual disappearance of fat 

 droplets from tissue fixed in formalin. However, I am not certain 

 that neutral fat is not affected by formalin fixation. Smith ('11) 

 in fact has found that ordinary formalin solutions hydrolyze 

 the fat droplets of frozen sections which are kept in the fixative. 

 I have frequently but not invariably found that the blue staining 

 of fat droplets with Nile blue is more marked in formalin fixed 

 material. Free fatty acids are soluble in Herxheimer's staining 

 solution and hence cannot be demonstrated by Herxheimer's 

 method. The fat droplets of formalin fixed material frequently 

 disappear, not being visible either as crystals or as droplets stain- 

 ing blue with Nile blue. This indicates that the final change 

 which takes place in the fat is not be to explained on the basis 

 of simple hydrolysis. I believe, however, that the initial change 

 may be hydrolysis of an unstable neutral fat. The fat droplets 

 of the muscle fibers of the ox fetus, for the most part, stain red 

 with Nile blue but after several days the droplets in the stained 

 section assume a blue color. This change of color indicates that 

 the fat is in an unstable condition and can be readily hydrolyzed. 

 The fat droplets of the fetal tissue were not permanently preserved 

 by formalin fixation. The observations of Bell and Smith, as 

 well as my own, are based on the use of ordinary commercial 

 formalin. This solution contains variable quantities of formic 

 acid and possibly acetic acid. The hydrolysis of the fat may 

 depend upon the presence of these impurities. It is thus possible 

 that the variable action of formalin is to be explained in part by 

 the variable chemical composition of the fixative. 



