866 



SCIENCE 



[N. S. Vol. XLIV. No. 1146 



The thesis is being printed by the Univer- 

 sity of Minnesota. 



Albert Ernest Jenks 



SPECIAL ARTICLES 



THE CHEMICAL CONSTITUTION OF CHITIN 1 



The prevalent ideas concerning the molec- 

 ular structure of chitin have been based upon 

 the fact that it gives off acetic acid when 

 acted upon by strong reagents, such as con- 

 centrated acid or alkali, and that its elemen- 

 tary composition suggests the empirical for- 

 mula C 8 H 1= ]Sr0 6 . 2 Since it is also known that 

 chitin yields on decomposition glucosamin it 

 was a logical inference that the above formula 

 represents an acetylated glucosamin 



CH»OH 



CHOH 3 



CH— NH— CH3CO 



CHO 



of which chitin is the polymere. 



This hypothesis regarding the structure of 

 chitin has been strengthened by other obser- 

 vations, viz., that if chitin is dissolved in 

 strong sulphuric acid, allowed to stand several 

 days and then diluted with a large quantity 

 of water, a white precipitate is formed which 

 on analysis proves to be a monoacetylgluco- 

 samin. Occasionally, however, a substance is 

 isolated which represents a monoacetyldiglu- 

 cosamin. 



An investigation upon chitin of lobsters 

 which I conducted recently at the Woods Hole 

 Fisheries Biological Laboratory brought out 

 certain facts which indicate that, while the 

 observations and analyses mentioned previ- 

 ously are doubtless correct, the hypothesis to 

 which they gave origin is based largely upon 

 misconception. I shall present here a brief 

 outline of the principal results of the investi- 

 gation, reserving a more detailed statement 

 for publication in the near future. 



It will not be necessary in this preliminary 



1 Published with the permission of the Com- 

 missioner of Fisheries. 



2 The formula actually computed from the 

 analytical data is C s H M NO , but C s H 16 NO is the 

 one usually given because it corresponds to the 

 hypothesis. 



note to discuss the experimental procedure 

 beyond the mere statement that pure chitin 

 was hydrolyzed with varying strengths of sul- 

 phuric acid, and for varying lengths of time, 

 the cleavage products as well as the volatile 

 substances formed during hydrolysis having 

 been quantitatively determined. 



The results of fundamental significance 

 yielded by this investigation are the following : 



First. Very little volatile acid is formed in 

 the early period of hydrolysis of chitin, though 

 all its glucose molecules may already be split 

 off. A very large production of volatile acid 

 is invariably found when the sugar molecule 

 itself is attacked by the acid medium. 



Second. The volatile acid produced is not 

 acetic only. At least in one experiment it was 

 possible to show that two per cent, of the acid 

 was formic. There is good reason for believing 

 that other volatile acids, too, may be formed, 

 but the attempt at isolating and identifying 

 those has not yet succeeded. 



Third. The maximum yield of sugar is 

 about 81 per cent. 



Fourth. The amino group is readily split 

 off from the glucosamine. The hydrolyzed 

 material contains the ammonium sulphate 

 which can be distilled off directly by making 

 it alkaline, and the ammonia can be collected 

 in standard acid. 



Fifth. The nitrogen of the amino group 

 does not represent the total nitrogen in the 

 chitin molecule. There is another nitrogenous 

 part in the molecule which is characterized by 

 great resistance, so that the nitrogen of that 

 small fraction can be obtained only by digest- 

 ing with concentrated sulphuric acid. There is 

 a remarkably constant relation between this 

 easily detachable nitrogen group and the 

 stabile nitrogen fraction. In my experiments, 

 the latter formed 12.04 to 12.45 per cent, of 

 the total nitrogen. 



The interpretation of these results is very 

 obvious. The chitin molecule is certainly more 

 complex than previously assumed. It may be 

 regarded as consisting of two parts : one con- 

 taining all the glucose and all the amino 

 groups, the other being a stable nitrogenous 

 compound which yields no glucose. It would 

 be venturesome at this time to express an 



