322 E. T. Bell, 



liposomes contain a small amount of olein mixed with some low-melting 

 fat that does not reduce osmic acid. 



Altmann believed that the droplets stained brown or grey with 

 osmic acid consist of olein mixed with vital substances. In the case 

 of faintly-refractive liposomes it seems probable that some ingredient 

 other than fat is mixed with the olein. On theoretical grounds an albu- 

 mino-lipoid seems probable. 



The extent to which osmic acid colors the liposomes is found to 

 vary with the species of the animal. Nearly all cats and some dogs 

 normally contain a large amount of osmic-staining fat in their muscle 

 fibers; but six pups and two adult dogs were found in which none of 

 the liposomes were colored at all by osmic acid. In the brown rat the 

 coarse liposomes may often be stained brown or black; but in the adult 

 ox it is seldom that any of the liposomes are colored at all. No osmic- 

 staining fat was found in the muscles of the rabbit, but only two animals 

 were examined. 



The nutritive condition is a factor of the greatest importance in 

 some animals. If a wild rat (ordinary brown rat, Mus decumanus) be 

 kept two days without food it loses about 20 per cent of its body weight, 

 the liposomes are greatly reduced in size, and none of them can be 

 stained at all with osmic acid. The liposomes of the rat are very sen- 

 sitive to changes in the food supply, and this factor alone will account 

 for the variations one finds in these animals. In the cat the staining- 

 power of the liposomes is also reduced by hunger, but they are not 

 liearly so sensitive as those of the rat. It is well known that the inter- 

 stitial granules of the muscle of the winter frog may be stained by 

 osmic acid, while those of the summer frog are not affected. 



Summarizing our knowledge of osmic acid we may say: 1. Osmic 

 acid is known to blacken oleic acid and triolein. It is not reduced by 

 palmatin, stearin, butyrin (Altmann), or their acids, or by sodium 

 oleate. It may stain lecithin a light grey-but this is not certain. It is 

 reduced by the more readily oxidizable metals, tannin, gallic and 

 pyrogallic acids, hydroquinone, etc. 2. Liposomes that stain black with 

 osmic acid are probably composed mainly of olein. 3. Liposomes that 

 are colored brown or grey probably contain some olein mixed with a 



