120 SCIENCE PROGRESS 



important information has been gained within the last year or 

 two : inosic acid. This substance was discovered by Liebig in 

 muscle and subsequently in meat extract. In overlooking its 

 phosphorus content, Liebig made one of his few mistakes. 

 Inosic acid is regarded as the simplest representative of the 

 nucleic acids, and it is the only one which can at present be 

 obtained pure (as a crystalline magnesium salt). Last year 

 Neuberg and Brahn, and independently Bauer, succeeded in 

 clearing up the constitution of this interesting compound. On 

 hydrolysis it furnishes a carbohydrate, a purine base and phos- 

 phoric acid. The purine base was identified as hypoxanthine 

 and the carbohydrate as a pentose (either 1-xylose or i-arabin- 

 ose). On partial hydrolysis, Neuberg and Brahn obtained a 

 pentose phosphoric acid. Similar ethereal compounds between 

 carbohydrates and phosphoric acid seem to be formed during 

 fermentation of sugars by zymase in the presence of inorganic 

 phosphates (Young, Iwanoff). 



Chlorophyll. — As the organic phosphoric acids, and especially 

 phytin, have been brought into close relationship with chloro- 

 phyll, an account of the progress made in the chemical knowledge 

 of this important respiratory pigment may be justified. 



Since the name " chlorophyll " was given to the green 

 pigment of leaves by Pelletier and Caventou in 1817, no sub- 

 stantial progress had been made in its chemistry until 

 Hoppe-Seyler, the pioneer of modern biological chemistry, 

 obtained crystalline derivatives from it. Most of our present 

 knowledge of chlorophyll is based upon the methods which 

 he introduced. The work of Schunck and of Marchlewski, in 

 Manchester, is also of fundamental importance. The researches 

 of Willstatter, which were only published last year, are based 

 on ingenious new methods. It is perhaps too early to estimate 

 the value of his work, though it may be the starting-point for 

 new discoveries in connection with the chemistry of chlorophyll. 



The pure native chlorophyll pigment has so far probably 

 never been isolated by anybody. It is a substance of such a 

 labile character, and so easily affected by light and air, that all 

 attempts to separate it have been in vain, and the statements 

 about pure crystallised chorophyll in the vast literature of the 

 subject are still awaiting confirmation. 



The whole of our knowledge about chorophyll is based on the 

 study of its cleavage products, produced by the action of acids 



