CHAPTER IV. 

 THE CARBOHYDRATES. 



WE designate by this name bodies which are especially abundant 

 in the plant kingdom. As the protein bodies form the chief portion of 

 the solids in animal tissues, so the carbohydrates form the chief por- 

 tion of the dry substance of the plant structure. They occur in the animal 

 kingdom only in proportionately small quantities, either free or in com- 

 binations with more complex molecules, forming compound proteins. 

 Carbohydrates are of extraordinarily great importance as food for both 

 man and animals. 



The carbohydrates contain only carbon, hydrogen, and oxygen. The last 

 two elements occur, as a rule, in the same proportion as they do in water, 

 namely, 2:1, and this is the reason why the name carbohydrates has 

 been given to them. This name is not quite pertinent, if strictly con- 

 sidered; because we not only have bodies, such as' acetic acid and lactic 

 acid, which are not carbohydrates and still have their oxygen and hydro- 

 gen in the same proportion as in water, but we also have a sugar (the 

 methyl pentoses, C 6 Hi2O 5 ) which has these two elements in another 

 proportion. At one time it was thought possible to characterize as car- 

 bohydrates those bodies which contained 6 atoms of carbon, or a multiple, 

 in the molecule, but this is not considered tenable at the present time. 

 We have true carbohydrates containing less than 6, and also those con- 

 taining 7, S, and 9 carbon atoms in the molecule. 



The carbohydrates have no properties or characteristics in general 

 which differentiate them from other bodies; on the contrary, the various 

 carbohydrates are in many cases very different in their external prop- 

 erties. Under these circumstances it is very difficult to give a positive 

 definition for the carbohydrates. 



From a chemical standpoint we can say that all carbohydrates are 

 aldehyde or ketone derivatives of polyhydric alcohols. The simplest 

 carbohydrates, the simple sugars or monosaccharides, are either alde- 

 hyde or ketone derivatives of such alcohols, and the more complex 

 carbohydrates seem to be derived from these by the formation of anhy- 

 drides. It is a fact that the more complex carbohydrates yield two or 

 even more molecules of the simple sugars when made to undergo hydro- 

 lytic splitting. 



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