838 PHYSIOLOGY 



diabetes. In many cases when the diabetic animal is living on a purely 

 protein diet, a uniform ratio has been found to exist between the glucose 

 or dextrose and the nitrogen excreted. 



equals generally 2-8. 



In certain other cases a constant D : N ratio of 3-65 has been found. The 

 former represents a conversion of 45 per cent., the latter of 58 per cent., 

 of protein into sugar. In a few cases however, even during complete 

 starvation, the ratio D : N has been found to be much greater than that 

 given above and to amount to as much as 10 or 12. These animals are 

 stated to be practically free from carbohydrates, so that the sugar excreted 

 in the urine can come only from the breakdown of proteins or fats. It is 

 impossible by any means whatever to break up a protein molecule so as to 

 get from it ten times as much dextrose as corresponds to the nitrogen, and 

 Pfliiger concludes that in cases where such a high D : N ratio exists the 

 dextrose must have been derived by a conversion of the fats of the body. 

 This conclusion is by no means generally accepted (cp. p. 852). If correct, it 

 would bear out the general statement made above, namely, that in the living 

 body practically all the chemical changes are reversible, and that the living 

 cell can so regulate the conditions of the reaction that the reversible reaction 

 becomes practically complete in either direction, the direction being deter- 

 mined by the needs of the body at the time. 



Accepting this generalisation, the chemical mechanism by which fats 

 are converted into carbohydrates must be the reverse of that by which 

 carbohydrates are changed into fats. The 2-carbon group split off from 

 the large fatty molecules would be utilised for the building up of the sugar 

 molecule. We know that such a synthesis can take place from such simple 

 groups as formic, gly collie, or gly eerie aldehyde. Though it is impossible 

 to deny to any cell of the body the power of effecting the conversion of 

 fats into carbohydrates, or carbohydrates into fats, the chief centre for 

 such conversions is probably the chemical factory of the body, namely, 

 the liver. It is significant that in the course of fatal diabetes, in which 

 the fat disappears entirely from the body, and there is wasting of prac- 

 tically all the tissues, the liver is the only organ which retains its weight 

 unchanged. During this disease there has been an enormous amount 

 of work done in the conversion of proteins and possibly of fats into carbo- 

 hydrates which could not be utilised by the body, .and the large size of 

 the liver at death suggests that the work of transformation has been performed 

 by this organ. 



