36 PHYSIOLOGICAL CHEMISTRY 



variations of this general process the plant undoubtedly can 

 build up a large number of other compounds of the most diverse 

 nature. 



The animal body has much more limited powers of synthesiz- 

 ing carbohydrates, although we now know that it is capable 

 of doing much more in this respect than was once thought. The 

 polysaccharide glycogen is regularly built up in the animal 

 body from monosaccharides, and it has been shown in diseases 

 where carbohydrates are lost from the body in the urine, that 

 certain compounds other than carbohydrates apparently can be 

 converted into sugar in the body. 



There are various methods for synthesizing carbohydrates in 

 the laboratory. One of these suggests the synthesis in plants. 

 If a solution of formaldehyde is made slightly alkaline, a con- 

 densation takes place, and the liquid will be found to contain 

 a hexose, acrose. 



A method which has proved very useful in studying the 

 carbohydrates is known as the cyanhydrin synthesis. This 

 serves to lengthen the carbon chain by one carbon atom. Start- 

 ing from a pentose, a hexose may be prepared, from a hexose 

 a heptose, and so on. The steps of the synthesis are as follows : 



CH 2 OH CHOH CHOH CHOH CHO+HCN-* 

 CH 2 OH CHOH CHOH CHOH CHOH^CN 



This nitril, containing six carbon atoms is easily saponified. 



HOH 



CH OH CHOH CHOH CHOH CHOH CN+HOH^ 



HOH 



CH 2 OH CHOH CHOH CHOH CHOH COOH+ 

 NH 3 +H 2 



Converting this into its lactone by the action of acid we get: 

 CH 2 OH CHOH CH CHOH CHOH C=0+H 2 



-O- 



On reducing this with sodium amalgam the compound takes 



