THE METABOLISM OF THE CARBOHYDRATES 315 



With regard to fat, there is no doubt that carbohydrates can 

 be ultimately converted into it (p. 285) in the organism ; but this 

 transformation is probably too slow to make it of much account 

 as an immediate means of disposal for the excess of carbohydrate. 

 Pavy, it should be mentioned, believes this conversion into fat 

 as well as into proteid to be an ever-occurring process, and if his 

 views, which we will discuss later, be accepted, little difficulty can 

 exist in explaining what becomes of the excess of ingested 

 sugar. 



Most workers agree that a certain amount of the absorbed 

 sugar is converted into, or ra,ther becomes incorporated with, the 

 tissue proteids, and in this way is laid aside in the organism ; but 

 just how much is thus disposed of cannot be stated. 



As the presence of a carbohydrate group in the proteid molecule 

 is now fully established, at least for most proteids, and since the 

 existence of this group has a very important bearing on the whole 

 question of carbohydrate metabolism, it will be advisable, before going 

 further, briefly to review the bio-chemical work which has been done 

 on this subject. 



The first exhaustive work in this direction was done by Schmiede- 

 berg ( 2 ). He found in cartilage proteid a complex polysaccharide 

 chondroitin-sulphuric acid. By hydrolysis of this substance he 

 obtained chondrosin and acetic acid, and by further hydrolysis of 

 chondrosin he thought that glycuronic acid and glucosamin were 

 formed. Glycuronic acid is, chemically, quite closely related to 

 dextrose, differing from it only in that the end CHOH group is 

 replaced by a COOH group. Glucosamin has recently been shown 

 by Emil Fischer to be a-amido-glucose. 



CHOH CHOH 



| (CHOH) 8 



(CHOH) 4 CH(NH) 2 



CHO CHO 



(Glucose) (Glucosamin) 



The presence of glucosamin in cartilage, if true, is of very great 

 interest from a biological point of view, for it is also found as a 

 constituent of the chitin found in the carapace of Arthropods (where 

 it is also in union with acetic acid) and in the so-called cellulose of 

 fungi. There is also reason to believe that it is present in the 

 insoluble residue of tubercle bacilli, 



