420 Histon and its Preparation [April 



II. HISTORICAL REVIEW OF HISTON PREPARATIONS 



Before proceeding to the description of my experiments the 

 reader may find it interesting to examine a brief summary of the 

 main points in this confusing Situation as brought out in the litera- 

 ture of the subject. 



I. Histons already prepared. The types of histons already 

 prepared, with indications of sources and names of the original 

 investigators, are shown in the appended summary : 



2. Methods of preparation. The methods of preparation are 

 indicated in the f ollowing summaries : 



A. GoosE-BLOOD histon: Kossel, 1884 (12), Preparation I. 

 Kossei centrifuged blood corpuscles free from plasma and then 

 dissolved them in water and ether. The residue was extracted with 

 water and ether until free from color and the final colorless mass 

 extracted with hydrochloric acid Solution, The acid liquid was 

 then saturated with sodium chlorid, the precipitated histon was 

 filtered off, and purified by washing with acidified sodium chlorid 

 Solution and then dialyzing against distilled water until free from 

 chlorid. The resulting Solution was then treated with an excess of 

 alcohol-ether and the precipitate dried to constant weight at 105° C. 

 Preparation IL In the second preparation the hydrochloric acid 

 Solution was precipitated with ammonia instead of sodium chlorid. 



B. Thymus HISTON : Lilienfeld, 1893 (19). Thymus glands 

 were freed from fat with a knife, minced and the hash pressed in a 



