CHAPTER III. 

 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 combination with more complex molecules, forming compound pro- 

 teins. 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 

 considered, because we not only have bodies, such as acetic acid and 

 lactic acid, which are not carbohydrates and still have their oxygen and 

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

 (the methyl pentoses, CeH^Os) which has these two elements in another 

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

 carbohydrates 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 

 containing 7, 8, 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 

 hydrolytic splitting. 



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