204 PRACTICAL PHYSIOLOGY 



orange with ammonia. The positive results show the presence 



of peptones. 



From these experiments we learn : 



(1) That proteoses and peptones give a pink biuret. 



(2) That they are not coagulable by heat. 



(3) That proteoses give a precipitate with HN0 3 soluble on 

 heating. Therefore, in the presence of other proteins, precipitated 

 by HN0 3 , such as albumin and globulin, they can be separated by 

 warming the solution and filtering hot . The precipitates of albumins 

 and globulins do not dissolve on warming. 



(4) Primary proteoses are salted out by half saturation with 

 ammonium sulphate. 



(5) Secondary proteoses are salted out by full saturation with 

 ammonium sulphate. 



(6) All proteins but peptones are salted out by full saturation 

 with ammonium sulphate. 



(The other products of protein hydrolysis are dealt with under 

 Digestion, pp. 226 and 306.) 



CHAPTER IV 

 CARBOHYDRATES 



Chemical Relationships. These are compounds of carbon, 

 hydrogen, and oxygen, in which the latter two elements usually 

 exist in the same proportion as in water. Their general formula is 

 therefore C m H 2w O M . 



Carbohydrates are found chiefly in vegetable tissues, but also 

 occur in animal tissues. They form very important food-stuffs, 

 for they are easily digested and assimilated, and moreover are much 

 cheaper than proteins and fats. The simplest form of carbohydrate 

 is called a monosaccharide, and all other carbohydrates can be 

 broken down into two or more monosaccharide molecules by the 

 chemical process of hydrolysis. When, by this process, two mono- 

 saccharide molecules are produced, the carbohydrate is called a 

 disaccharide ; when more than two are produced, the carbohydrate 

 is called a polysaccharide. The monosaccharides and disaccharides 

 being sweet to the taste are together spoken of as sugars. 



I. Monosaccharides 



Chemically considered, monosaccharides are either aldehydes or 

 ketones ; the former are called aldoses, the latter ketoses. The 

 sugars are classed according to the number of carbon atoms in the 

 molecule, e.g. pentose C 5 H 10 O 5 , hexose C 6 H 12 O 6 . 



Aldoses. An aldehyde is the first oxidation product of a primary 

 alcohol, and it contains the end group CHO. 



A primary alcohol is one in which the " OH "or " hydroxyl group " is 



