METABOLISM 39 



It is interesting to note that it is only those sugars 

 which are directly fermentable by yeast which are 

 capable of conversion into glycogen, and of subsequent 

 utilization in the body. Unfermentable sugars, such as 

 cane-sugar and lactose, if they reach the blood-stream 

 as such, are excreted by the kidney. It is for this reason 

 that these sugars are unsuitable for administration 

 hypodermically in artificial feeding, and the same fact 

 explains the tendency for nursing women to suffer from 

 lactosuria ; for if lactose is reabsorbed from the mammary 

 glands, it cannot be burnt up in the body, but is excreted 

 in the urine. 



It is further noteworthy that it is only those sugars 

 which contain three carbon atoms, or a multiple of that 

 number, which are capable of direct fermentation, and 

 therefore of conversion into glycogen. Those which con- 

 tain five, seven, or any other number of carbon atoms 

 cannot be so converted, and should they gain access to the 

 blood, are only with difficulty destroyed, and are apt 

 to be excreted in the urine. Now, sugars with five 

 carbon atoms (pentoses) commonly occur in certain 

 fruits, and hence pentosuria, as it is termed, is a not 

 infrequent consequence of the free consumption of such 

 foods. 



It must be remembered that there is a limit to the 

 capability of the liver to convert soluble carbohydrates 

 into glycogen. If the amount of carbohydrates con- 

 sumed be excessive, the liver may not be able to keep 

 pace with the supply, with the result that some escapes 

 conversion, and passing into the general circulation is 

 excreted by the kidney. To this the term alimentary 



