CEREBROSIDES AND KYDROCARBONS 7 



endotliolial system. It is believed that, in this case also, the cerebrosides 

 originate at the site wliere they are deposited, rather than that they are 

 carried to the latter organs from the brain. The chief aigiiment for this 

 hypothesis is the demonstration that the: cerebroside in th(! })rain is a 

 galactolipid, while that in the spleen is largely, if not entirely, a ghicolipid. 

 Hydrocarbons are a})sorl)ed to only a small extent })y the higher animals. 

 Certain species of animals, including man, are able to absorb jS-carotene 

 from the gastrointestinal tract, and to transport it to the liver and other 

 tissues. It is believed that this is effected by means of a carotenoid- 

 protein combination which is present in the blood. Mineral oil is another 

 hydrocarbon which can be absorbed to some extent. It has been demon- 

 strated that this substance accumulates in the liver. The mechanism 

 by which such hych'ocaibons aie metabolized and ultimately removed 

 from the tissues is not clear. For a complete exposition of the various 

 phases of digestion, absorption, transport, and storage of the several 

 lipids, the reader is referred to The Lipids, Volume II. 



