Chemical Constituents of the Animal Body. 219 



saccharoses are known containing two up to nine carbon 

 atoms, and according to the number they are designated 

 bioses, trioses, tetroses, etc. They are either aldoses (alde- 

 hydes), or ketoses (ketones), containing hydroxyl groups, 

 and give the ordinary aldehyde and ketone reactions. 

 Of these, the most important are the reducing actions 

 (with Fehling's solution), and the formation with phenyl- 

 hydrazine of characteristic derivatives known as the 

 osazones. By virtue of the asymmetric carbon atoms, 

 large numbers of stereoisometric forms are known, which 

 in the case of the pentoses and hexoses have been considered 

 in some detail. The methods by means of which the steric 

 relationships of these isomerides to one another can be 

 ascertained have been discussed, and it has been pointed 

 out that differences in the space positions of various 

 groups are of great biological importance. The sugars 

 also form derivatives known as the glucosides, a large 

 number of which are found native. Certain simple 

 glucosides have been obtained synthetically, in which are 

 found characteristic examples of stereoisomerism. 



Part III. The Proteins. 



The chief constituents of animal tissues are nitrogen- 

 containing substances known as the albuminoid substances 

 or proteins. Similar products are also widely distributed 

 in plant tissues. In spite of the fact that they differ very 

 widely from one another in their physical properties, and 

 have in many cases no outward resemblance to one another, 

 these substances belong to a well-defined chemical class. 

 A typical member is the chief protein constituent of the 

 white of egg, albumin, which name was formerly employed 

 to designate all other members of the group. The proteins 

 are chemically characterized by the fact that they yield, on 

 hydrolysis with mineral acids, a mixture of amino-acids. 



