128 



PHYSIOLOGY 



exposed to sunlight for a considerable time it undergoes decomposition 

 with the formation of lactic acid. Thus : 



glucose 



2C 3 H 6 3 



lactic acid 



This change of glucose to lactic acid under the catalytic influence 

 of the alkaline calcium hydrate probably occurs by means of a shifting 

 of the elements of the water, a process which in many long chains 

 seems to occur with considerable facility, and is dependent on the 

 spatial configuration of the molecule involved. Thus the change of 

 sugar to lactic acid is readily effected by means of many micro- 

 organisms in the case of glucose, fructose, and mannose. but with 

 considerable difficulty in the case of galactose. In the three former 

 sugars the atoms round the two middle carbon atoms of the chain 

 are disposed thus : 



OH.C.H 

 H.C.OH 



or 



H.C.OH 

 OH.C.H 



When either of these arrangements reacts with water, thus 

 CH 2 OH CH 2 OH 



CHOH 



OH.C.H 



OH 



CHOH 



COH H0 



HCOH 



CHOH 



H 



CH 2 OH 

 CHOH 



COH COH 



we obtain two molecules of glyceric aldehyde, which then by a further 

 shifting of the OH and H groups becomes 



CH 3 



i 



CH.OH 

 COOH 



lactic acid 

 Lactic acid with ammonia and some dehydrating agent will give ammo- 



