108 PHYSIOLOGICAL CHEMISTRY. 



cipal member of the group is the haemoglobin of the blood. Upon 

 hydrolytic cleavage this haemoglobin yields a protein termed globin 

 and a coloring matter termed hcemochromogen. The latter sub- 

 stance contains iron and upon coming in contact with oxygen is 

 oxidized to form hamatin. Hamocyanin, another member of the 

 class of haemoglobins, occurs in the blood of certain invertebrates, 

 notably cephalopods, gasteropods, and Crustacea. Haemocyanin 

 generally contains either copper, manganese, or zinc in place of the 

 iron of the haemoglobin molecule. 



The lecitho proteins include such substances as lecithans and 

 phosphophatides which consist of a protein molecule joined to leci- 

 thin. They have been comparatively little studied until recently, 

 and in much of the older research they were undoubtedly con- 

 sidered as lecithins. 



For experiments on conjugated proteins see pages 56, 195, 196, 

 199, 201, 203, 223 and 228. 



DERIVED PROTEINS. 



These substances are derivatives which are formed through hy- 

 drolytic changes of the original protein molecule. They may be 

 divided into two groups, the primary protein derivatives and the 

 secondary protein derivatives. The term secondary derivatives is 

 made use of in this connection since the formation of the primary 

 derivatives generally precedes the formation of these secondary 

 derivatives. These derived proteins are obtained from native 

 simple proteins by hydrolyses of various kinds, e. g., through the 

 action of acids, alkalis, heat or enzymes. The particular class of 

 derived protein desired regulates the method of treatment to which 

 the native protein is subjected. 



Primary Protein Derivatives. 



The primary protein derivatives are " apparently formed through 

 hydrolytic changes which involve only slight alterations of the 

 protein molecule." This class includes proteans, metaproteins, and 

 coagulated proteins. 



PROTEANS. 



Proteans are those insoluble protein substances which are pro- 

 duced from proteins originally soluble through the incipient action 

 of water, enzymes, or very dilute acids. It is well known that 



