450 CHEMISTRY OF THE PROTEIDS CHAP. 



excess of acids, specially mineral acids, they pass into solution again, 

 and then may undergo disintegration. The salting-out limits differ 

 with each nucleo-proteid. The nucleo-proteids are under suitable con- | 

 ditions as readily and as completely coagulated and denaturalised 

 by heat or other agencies as are the native albumins, but the nucleic 

 acid may be recovered from the coagulum in an unaltered state, for 3 

 only the albumin component becomes coagulated. 



Nucleo-proteids give all the colour-reactions of the albumins, and 

 are precipitated by the ordinary precipitating agents. They yield, 

 as far as they have been investigated, the dissociation-products of the 

 ordinary albumins, but in addition also products peculiar to the 

 nucleic-acid radical, namely, the nuclein-bases, etc., and above all 

 phosphoric acid. Their percentage -composition varies greatly and 

 can be given, with a fair amount of assurance, only in the case of a j 

 few substances. 



Iron is contained in most, if not in all, nucleo-proteids, and if we 

 except the iron present in the haemoglobin, the main bulk of the j 

 remaining iron concerned in metabolism is contained in the nucleo- 

 proteids ; nothing is known as to how the iron is linked up, but we 

 know that it is present in a non-ionic or ' masked ' state, and that 

 therefore it cannot give directly the Prussian blue reaction, or the 

 ammonium -sulphide- or haBmatoxylin - tests. That plasminic acid 

 behaves similarly has been pointed out on p. 447. 



The methods of unmasking iron for micro-chemical research have 

 been studied by Molisch, 1 and especially by Macallum. 2 The micro- 

 chemical reactions of nuclein- compounds is fully discussed in the ' 

 author's Physiological Histology, 1902. 



The occurrence of copper in place of iron in certain leucocytes of 

 the oyster has been described by Boyce and Herdman. 3 



On digesting nucleo-proteids with pepsin-hydrochloric acid, the 

 albumin-moiety breaks up into albumoses and peptones, while the 

 nuclein is precipitated. This property of giving a precipitate with 

 pepsin-hydrochloric acid led originally to the discovery of nucleo- 



1 Molisch, 'Bemerk. li. d. Nachweiss von maskirtem Eisen,' Ber. d. deutsch. bot. 

 Qesellsch. 11. 73 (1893). 



2 A. B. Macallum, ' On the Distribution of Assimilated Iron Compounds, other than 

 Haemoglobin and Haematins, in Animal and Vegetable Cells,' Quarterly Journ. of 

 Microsc. Science, 38. 175 (1895-96), and 'A New Method of distinguishing between 

 Organic and Inorganic Compounds of Iron,' Journ. of Physiol. 22. 92 (1897). 



3 R. Boyce and W. A. Herdman, Phil. Trans. Lond. 62. 34 (1897-98). 



