 chang sphingosin fatti acid compon gangliosid develop rat human brain rat brain increas weight birth three stage rapidli 2 week ii lower rate 2 5 week iii lower rate 5 week 5 month succeed period design iv maintain constant weight 1 year ag brain gangliosid content increas linearli ii slowli iii diminish iv appear measur amount brain sphingomyelin cerebrosid succeed gangliosid ceramid -sphingosin fatti acid larg proport three sphingolipid appear measur quantiti fatti acid cerebrosid rapidli declin neglig level gangliosid sphingomyelin declin slowli remain major fatti acid compon cerebrosid sphingomyelin contain -sphingosin exclus stage rat brain growth gangliosid contain -sphingosin exclus birth subsequ accumul -sphingosin equal quantiti base type chang human brain gangliosid resembl rat tai-sach diseas gangliosid -sphingosin high content fatti acid 