184 ON VARIABILITY AND ADAPTATION 



viction that some of them give origin to myelin globules. These 

 lecithins, I may remind you, dissociate into fatty acid, glycero- 

 phosphoric acid and cholin. According to Carbone, in dis- 

 sociation they may give rise to fatty acids, neutral fats, and 

 cholesterin. Here once more we have this suggestive appear- 

 ance of the two substances of widely different chemical nature, 

 cholin and cholesterin, each of which we have found associated 

 with the development of myelin globules. 



From the tissues there have been gained a di-oleo-lecithin, a 

 di-stearo-lecithin, and a palmito-stearo-lecithin. 1 They also, it 

 will be seen, are fatty acid compounds. They afford " myelin 

 figures " of a simple type and doubly contoured myelin droplets, 

 but thus far with the pure substances free from cholesterin I 

 have been unable to gain doubly refractive globules. 2 It is 

 deserving of note that the two tissues affording myelin in greatest 

 amounts contain normally the most abundant lecithin, namely, 

 the brain and the adrenals, and that, as Albrecht has pointed 

 out, the abundant " myelin " obtained from the red corpuscles 

 is composed in the main of lecithin. More particularly is it in 

 connexion with autolysis, and the self-digestion of tissues that 

 the association of lecithin and the appearance of " myelin bodies" 

 has of late been commented on from various quarters. Time 

 forbids that I should enter at length into this most interesting 

 field. I can only very rapidly point out that if a sterile organ 

 be kept with all aseptic precautions at the body temperature, 

 its cells in the course of a few hours exhibit abundant small 

 rounded irregular bodies in their cytoplasm, possessing double 

 contour. Coincidently, the nuclei become pale and it can be 

 made out (Albrecht, Dietrich and Hegel) that the chromatin 

 becomes discharged into the cytoplasm, the appearance of the 

 myelin bodies bearing a definite relationship to the discharge 

 of the chromatin. 



Some but not all of these afford obscure double refraction. 

 As indicated by the accompanying table from Waldvogel and 

 Mette, while in autolysis of the fiver the ethereal extract (of 

 total fatty substances) is not greatly increased, the fatty acids 

 and neutral fats in the cell undergo great increase at the expense 

 of the lecithin, as does also the cholesterin. 



1 According to the recent very full studies of Thudiohum every true lecithin 

 contains at least one oleic acid radical. - Vide note on page 172. 



