The Interstitial Granules of Striated Muscle etc. 319 



Starke [1891, 1895] contended that palmatin and stearin are also 

 blackened if the preparation de kept in 80 per cent alcohol for 24 hours 

 after the osmio treatment. He called attention to a large number of 

 granules in the frog hver (Rana esculenta) that are colored brown by 

 the direct osmic treatment, but change to black after the secondary 

 treatment in alcohol. 



Handwerck [1898] admits the accuracy of Starke's observations 

 but does not agree with his interpretation of them. He finds that pure 

 palmatin and stearin are not blackened at all by osmic acid even after 

 the secondary treatment in alcohol. But some blackening may be ob- 

 tained if a trace of olein be added to pure palmatin or stearin. Osmic 

 acid is a very delicate reagent for oleic fat. The droplets in the tissues 

 that stain brown by the direct osmic treatment owe their color to the 

 presence of a small quantity of olein. 



Mulon [1904] agrees essentially with Handwerck. He states that 

 the secondary blackening in alcohol cannot be obta'ned w'th pure 

 palmatin and stearin. His conclusions are: 1. All fat in the tissues that 

 is blackened directly under the influence of osmic acid is composed for 

 the most part of olein. 2. All fat in the tissues which turns yellow or 

 brown in osmic acid is composed for the most part of palmatin and 

 stearin, but contains a small quantity of olein. It is poorly fixed by 

 osmic acid and is therefore readily soluble in the essences after this 

 reagent. Brown fat is apt to become black by the action of weak alcohol. 

 3. Since lecithin is poor in olein it would belong to the group which 

 stains brown. 



My own observations are in accord with those of Altmann. Finely 

 ground palmitic and stearic acid were rubbed on cover glasses and 

 stained over night in 1 per cent osmic acid. The particles are colored 

 only a light grey. But it appeared possible that the fats were not blacken- 

 ed because they were solid. Smears were therefore made of the melted 

 fats and put in 1 per cent osmic acid at a temperature slightly above 

 the melting point of the fat. The melted fats were exposed to the action 

 of osmic acid in this way for about six hours. Some blackish spots may 

 appear in the smear but nearly all of it remains a light grey. Droplets 

 of oleic acid are stained intensely black by osmic acid solutions. 



