308 E. T. Bell, 



tissue. The granules are stained with varying degrees of intensity. It 

 stains many granules not shown by other fat stains. It must 

 however be used with caution to guard against precipitates. It is very 

 essential that iresh tissues be used if all the liposomes are to be shown. All 

 the fixatives that have been tried affect the liposomes to a greater or 

 lesser extent, sometimes removing all of them in a few hours. The 

 method of staining is as follows: Small well-teased specimens of fresh 

 tissue, or thin frozen sections are rinsed in 70 per cent alcohol about 

 1 minute to remove the water. After 5 to 10 minutes in the stain, the 

 specimen is removed with a needle and shaken in 70 per cent alcohol 

 10 to 20 seconds to remove the excess of the stain. It is then quickly 

 transferred to water to remove the alcohol. After 2 or 3 minutes in 

 water it may be mounted in glycerin. Specimens should always be 

 mounted in water and potassium hydroxid for controls, at least until 

 the technique is thoroly mastered. 



The dark and light fibers. A frozen section of fresh vertebrate 

 muscle examined in normal salt solution^) usually shows two types of 

 fibers, the so-called dark and light fibers. The differences are much 

 better brought out if the section be stained with Herxheimer's scarlet 

 red (figs. 1 — 3 and 5). In general the dark fibers contain a number of 

 coarse, strongly-refractive liposomes, and their protoplasm is stained 

 to a considerable degree ; the light fibers usually contain small, faintly- 

 refractive liposomes, and their protoplasm is only faintly colored. The 

 opacity of a dark fiber may be due to a large number of small liposomes. 

 The number, size, and staining-properties of the liposomes depend upon 

 the species of the animal, its nutritive condition, etc. In very emaciated 

 animals nearly all differences between the dark and light fibers may have 

 disappeared (figs. 2 and 7). All possible intermediate forms between 

 typical dark and light fibers may often be found in the same muscle. 

 It is more accurate to speak of dark, hght, and intermediate fibers. 



The terms "dark" and "light" seem to have only a relative mean- 

 ing. The darkest fibers of some animals, such as the adult ox (fig. 3), 

 do not contain any coarse droplets. They correspond to the intermediate 



^) The dark and light fibers cannot be distinguished if the unstained specimen 

 be mounted in alcohol or glycerin. 



