Chemical Constituents of the Animal Body. 249 



given tissue is, however, small. The tissues which have 

 been chiefly employed for their preparation are the ripe 

 spermatozoa of fish, the thymus gland, testicular substance, 

 and yeast cells. 



Nucleo-proteins were first investigated in some detail 

 by Miescher, who isolated them from the spermatozoa of 

 fish. As these cells consist to a large extent of nucleus, 

 and as, furthermore, they yield a large amount of nucleo- 

 protein, the conclusion was drawn that nucleo-proteins are 

 the chief constituent of the nucleus. It was found that 

 the matured testicle of salmon and other fish contained a 

 very basic protein, belonging to the class of protamines, 

 combined with a moderately strong acid which contains 

 phosphorus as an essential constituent, which was called 

 nucleic acid. On extracting the disintegrated spermatozoa 

 with solutions of mineral acids, the protamine is separated 

 from the nucleic acid and converted into a salt of the 

 mineral acid, which can be precipitated from the aqueous 

 solution by the addition of alcohol. 



The general method of preparing nucleo-proteins consists 

 in extracting the tissues with either water or dilute alkali 

 and precipitating the nucleo-protein by very dilute acid. The 

 tissue, before extraction, is generally treated with alcohol 

 which withdraws the water and extracts the fats. A pro- 

 duct is thereby obtained which can be ground into a powder. 



The nucleo-proteins from fish spermatozoa contain, as 

 already stated, the basic protein prolamine combined with 

 nucleic acid. Other nucleo-proteins are formed by the 

 combination of nucleic acid with less basic proteins. On 

 treatment with pepsin the protein part of the molecule is 

 partially hydrolyzed, and a residue, known as a nuclein, is 

 obtained, which contains the nucleic acid in combination 

 with the degraded protein residue. 



Nucleic Acid. The most essential part of the nucleo- 



