THE PROTEIN SUBSTANCES. 1 03 



solution free from salt is not coagulated on boiling, but with 

 a little salt present coagulation follows. They are precipitated 

 by nitric acid ; the precipitate dissolves on heating but appears 

 again on cooling. They yield precipitates with the alkaloid 

 reagents in neutral as well as in weak acid solutions. Histone 

 solutions added to neutral and salt-free solutions of several 

 native albumins yield complex precipitates which contain for 

 one molecule of the histone one or more molecules of the other 

 protein. This is an important reaction as it suggests the build- 

 ing up of a complex protein molecule, with the histone as a 

 component group. 



The histones are strongly basic bodies with a relatively 

 large content of nitrogen; they have not yet been isolated in 

 crystalline condition. They give the biuret reaction and the 

 xanthoproteic reaction, but contain no carbohydrate group, or 

 phosphorus. Several of them, perhaps all, contain iron, which 

 is important. 



The best known histones are these: 



Globin. This makes up about 96 per cent of the hemo- 

 globin of the red blood corpuscle, existing in combination with 

 the iron-containing constituent, hematin. 



Scombron, Salmon, Arbacion. These are peculiar his- 

 tones which have been isolated from the spermatozoa of the 

 mackerel, salmon and sea urchin. Preferable names are scom- 

 ber-histone, salmo-histone, etc. The on termination may be 

 reserved for the protones. 



Nucleo-histone. This name was given to a product sepa- 

 rated from the thymus glands of the calf and was one of the 

 first studied. 



The Nucleinic Acids. The occurrence of these important 

 compounds in combination with protamines has been referred 

 to several times in the last few pages. By different processes 

 of separation a number of these acids have been obtained from 

 various cell structures, and especially from yeast and fish 

 sperm or spermatozoa. The results of analyses lead to for- 



