160 LECTURE VIII. 



the close relationship of glucosamine to the amino acids as well as to the 

 carbohydrates. This is very evident from the following comparison: 



CH 2 . OH CH 2 . OH CH 2 . NH 2 



CH .OH CH . OH CH 2 



CH.OH CH.OH CH 2 



CH .OH CH . OH CH 2 



CH.OH CH.NH 2 CH.NH 2 



CH : O CH : O COOH 



Glucose Glucosamine Lysine 



It is not right to consider as exceptional the albumins containing carbo- 

 hydrate groups. It is more correct, according to our present knowledge, 

 to speak of albuminous bodies characterized by a high content of gluco- 

 samine, just as we know of proteins which have considerable glycocoll. 

 Just as there are proteins which contain only small amounts of glycocoll, 

 and some with none at all, so we also recognize proteins which possess 

 small quantities of glucosamine, as well as those which have none of this 

 hexose base. The fact that other amino sugars probably participate in 

 the constitution of proteins does not affect this conception. It is doubtful 

 whether nitrogen-free sugars occur in albumin. It must also not be 

 forgotten that the presence of glucosamine, as a primary cleavage-product, 

 is doubted. A complex carbohydrate has been assumed to be the ante- 

 cedent of the glucosamine. The results at present are not sufficiently 

 exact to settle the question. 1 The conception that the " carbohydrate- 

 group " is a constituent of the albumin molecule in the same sense as the 

 amino acids, is rendered somewhat improbable by the fact that various 

 observers have obtained entirely different carbohydrate values in the 

 analysis of one and the same substance. It has even been suggested that 

 specific proteins, e.g., serum-albumin, unite with the sugars, conduct 

 them to the tissues, and finally give them up to the latter. Such an 

 assumption would be comprehensible if it were known that the carbo- 

 hydrate groups were loosely bound to the albumin molecule. This, 

 however, is not the case. A more satisfactory explanation would be 

 that the varying carbohydrate content of the proteins was due to the 

 albumins investigated not being identical. 



As yet we know but little about the quantities of glucosamine present 

 in the mucins, the proteins richest in carbohydrates. It is only known 



1 L. Langstein: Ergebnisse der Physiologie (Asher and Spiro), 1, 63 (1902); 3, 453 

 (1904). 



