THE PROTEIN SUBSTANCES. 



HEMOGLOBINS. 



The discussion of the important subject of hemoglobins 

 may properly be left to be taken up with the study of the blood 

 in which they are contained. The term is used here in the 

 plural since from different kinds of blood bodies of somewhat 

 different properties have been obtained. Hemoglobin in gen- 

 eral must be classed among the compound bodies because it is 

 distinctly made up of two characteristic parts, a histone, 

 already referred to, and hematin. 



GLUCO-PROTEIDS. 



AYe have here a group of bodies containing a number of 

 important members about which our knowledge in most cases 

 is not very extended or exact. As the name indicates the pro- 

 teins here concerned contain a carbohydrate constituent which 

 may be recognized by its reducing properties when the sub- 

 stance in question is warmed with a weak acid and afterwards 

 treated with Periling' s solution in the usual way. The carbo- 

 hydrate group separated appears to be, in most cases at any 

 rate, glucose amine. Familiar illustrations of these gluco-pro- 

 teids are found in the mucins and related bodies called mucoids. 

 As a class these substances are characterized by relatively low 

 nitrogen and high oxygen content, due to the presence of the 

 carbohydrate group. The amount of carbon present is also 

 lower than in the common proteins. Of the exact nature of 

 the albumin combined with the carbohydrate little is known, 

 because in separating the two groups by acid or alkali treat- 

 ment the protein constituent is so changed that no safe conclu- 

 sion can be drawn as to its original nature. 



The gluco-proteids behave as acid bodies. They are not 

 coagulated by heat alone, but heating with acids or alkalies 

 produces a complete alteration. With weak acetic acid a pre- 

 cipitate is in most cases formed which is not easily soluble in 

 excess. 



Mucins. These bodies are found in various secretions, 



