THE PROTEIN SUBSTANCES. 75 



Following the coagulation, which appears in most cases, a 

 gradual hydration and solution begins, and a small portion of 

 the substance is brought into the form of albumose or pos- 

 sibly peptone. At a higher temperature, that is, by heating 

 with water or steam under pressure, more profound changes 

 take place. Ammonia and hydrogen sulphide are split off 

 from the molecule and relatively large amounts of albumose 

 and peptone are formed. If the temperature is high enough 

 the reaction extends to the complete destruction of the mole- 

 cule and such bodies as leucine and tyrosine are produced in 

 quantity. 



Effect of Alkalies. Much more decided changes are 

 noticed when the protein body is heated with alkali solutions. 

 Experiments of this kind were long ago carried out by 

 Schiitzenberger and have since been frequently repeated. 

 Numerous compounds have been identified among the decom- 

 position products, and of these the most important are leucine 

 in quantity, tyrosine, ammonia, carbonic acid, butyric acid, 

 formic acid, acetic acid, oxalic acid, aspartic acid, amino- 

 valeric and amino-butyric acid. Barium, potassium and 

 sodium hydroxide solutions have been used for the purpose. 

 By melting the dry proteins with alkali some of the same 

 products are formed, especially leucine and tyrosine. 



Effect of Acids. Many experiments have been made on 

 the decomposition of protein bodies by boiling with acids, and 

 particularly with strong hydrochloric acid, the hydrolyzing 

 power of which is very great. The most important of the 

 products isolated in this way are the following: 



THE HEXONE BASES. The term hexone bases has been 

 given by Kossel to a group of bodies which occur commonly 

 in the decomposition products of practically all the protein 

 substances. We have here arginine, C 6 H 14 N 4 O 2 , lysine, 

 QH 14 X 2 O 2 , and histidine, C G H 9 N 3 O 2 . The first appears to 

 be a guanidine derivative of amino-valeric acid, the second is 

 diamino-caproic acid, while the third appears to be a diamino 

 acid of composition as yet unknown. The isolation of these 



