GEANULES AND FAT OF STRIATED MUSCLE 21 



after most decided post mortem changes had taken place. Fat 

 droplets in the human cardiac fibers are commonly regarded as 

 occurring only under pathological conditions. I believe that a 

 thorough investigation of the subject, with the aid of the best 

 technique would demonstrate that fat droplets of small size are 

 of nomial occurrence in human cardiac muscle fibers. 



Fetal muscle. Kainath ('04) examined the skeletal muscles 

 of the ox fetus. He found fine fat droplets in the fibers from the 

 3.5 to the 12.5 cm. stage but none were present in the fetus of 

 20 cm. and 40 cm. Bell ('09) found fat in the muscle fibers of 

 the ox fetus from the 7 to the 28 cm. stage, but observed none in 

 the fibers of seven fetuses of later stages. 



The muscle fibers of the early fetus were not examined in this 

 study but I have found a large amount of fat in the fibers of the 

 ox fetus from the 35 cm. stage to full term. The dark fibers con- 

 tain many fat droplets while light fibers have but a small number. 

 I have also examined the skeletal muscles of a seven months and 

 eight months human fetus. The dark fibers were crowded with 

 fat droplets. 



V. CHEIVIICAL NATURE OF INTERSTITIAL GRANULES AND 



FAT DROPLETS 



A qualitative chemical analysis, in vitro, of the true intersti- 

 tial granules and fat droplets of muscle fibers is beset with 

 obvious difficulties and such an investigation has never been 

 attempted. One can, however, draw certain conclusions respect- 

 ing the chemistry of these bodies by a consideration of the nature 

 of the various methods used in demonstrating them in tissue sec- 

 tions. 



a. Chemical nature of true interstitial granules 



Kolliker ('57) states that the true interstitial granules, being 

 very pale, especially in mammalian muscle, have been overlooked 

 by previous observers. He finds the granules insoluble in alcohol 

 and ether. Kolliker ('88) concludes that, chemically, the gran- 

 ules are identical with no known substance. They contain no 

 glycogen for they do not give the iodine reaction. Retzius ('90) 



