ELEMENTS OF COMPOSITION. 



29 



C 2 H 



OTT 



\/n TT \ QTT 



palmitic and 



may be split up into neurin, (cholin) = 



oleic acid, and glycerophosphoric acid. 



Lecithin may be derived from glycerophosphoric acid, in which the 

 two hydroxyl hydrogens of the glycerin are replaced by the radicals of 

 palmitic and elaidic acids, at the same time that the neurin (half alcohol 

 and half base) forms with the glycerophosphoric acid an ether-acid. Its 

 formula is therefore 



C^ TT (~\ 



O.PO 



OH 

 O.C 2 H 4 (CH 3 ) 3 ^.OH. 



This substance, besides being found in nervous tissue, is also found in 

 the yelk of the eggs of hens, in the blood-corpuscles, in bile, semen, and 

 pus. There appear to be various kinds of lecithin in nature. 



Protagon, a substance described some years ago by Liebreich, is simply 

 a mixture of cerebrin and lecithin. 



By myelin, as described by Virchow, we understand a substance of 

 peculiar microscopic appearances occurring in different parts of the body, 

 especially in those undergoing decomposition. It has a characteristic 

 dull lustre (fig. 4), and is usually met with in masses of roundish, oval, 

 filiform, looped, or lobulated figure, with double outline. Myelin is 

 tinged slightly brown by iodine, while in concentrated sulphuric acid it 

 becomes of a red, or at times violet, colour. It resembles cerebrin and 

 lecithin in its property of absorbing hot water, and 

 swelling up into a gelatinous mass, and also in its rela- 

 tions of solubility to alcohol and ether. Myelin drops, 

 however, may be obtained from compounds of quite a 

 different nature, as, for instance, from oleic acid and 

 ammonia (Neubauer). Myelin is therefore chemically 

 untenable as a special combination. 



Another allied substance, known as amyloid, may be 

 also mentioned here. This appears in peculiar homo- 

 geneous masses of dull lustre, and is probably a mixed Fig. 4 

 degeneration product of many, especially glandular por- 

 tions of the body (waxy or lardy degeneration). Amyloid matter is 

 coloured of a peculiar reddish-brown or brownish- 

 violet with a solution of iodine, which turns to violet 

 usually on the subsequent addition of concentrated 

 sulphuric acid, or, more rarely, to blue. 



We turn finally to the corpuscula cimylacea, 

 round or bilobular structures of very variable size, 

 which bear a strong resemblance to granules of 

 starch, whence the name. They are sometimes 

 laminated, sometimes not, and vary in their re- 

 actions, becoming violet under the action of iodine 

 and sulphuric acid, but frequently blue or bluish 

 with iodine alone. Thus they resemble amylum in 

 one respect, and cellulose in another, although we are not justified in re- 

 ferring them to either of these substances. 



The corpora amyiacea are to be found in the nervous centres of putre- 

 fying corpses, and, moreover, in quantity increasing with the advance of 



Different forms 



/*\ 



\|y 



. Corpnscuia amyiacea 



from the human brain. 



