II 

 ON THE OCCURRENCE OF MANGANESE 

 IN LAND AND FRESH WATER MOLLUSCA. 



Prof. A. E. BOYCOTT, M.D., F.R.S , etc. 



The present investigation originated in the observations of 

 H. C. Bradley 1 on the occurrence of considerable quantities 

 of manganese in fresh-water mussels in North America. Ex- 

 amining hundreds of specimens of Anodon and Unio from many 

 different localities (the species are not particularised), he 

 constantly found manganese to the«extent of about i per cent, 

 of the dry weight of the animal ; the shell contained about 

 0-15 per cent., mostly in the nacre 2 ; a manganiferous 

 Crenothrix formed an important food of the mussels, and he 

 suggests that the occurrence of this Crenothrix (and possibly 

 other organisms which accumulate manganese) may determine 

 the distribution of the molluscs. His observations are of much 

 interest, especially as throwing light on the natural foods of 

 mollusca (a matter on which there is little accurate knowledge), 

 and indicating lines which may explain some of those curiosities 

 of distribution and habitat which are familiar to field naturalists. 



Following these indications, I have briefly explored such of 

 our British land and fresh-water mollusca as I have been able 

 to obtain, or which I happened to have by me, fifty-six 

 in number. The results seem interesting enough to put forward 

 in their present incomplete state in the hope that others will 

 pursue the matter and help to clear up many points at present 

 in doubt. The bodies alone have been investigated, and I 

 know nothing of the occurrence of manganese in the shells. 



The method of analysis is that indicated by Bradley and 

 Bertrand. 3 The tissue, dried at ioo°C, is burned., fused with 

 potassium nitrate (the presence or intensity of green giving 

 a good idea of quantity of manganese), dissolved in dilute nitric 

 acid, strong nitric acid and solid potassium persulphate added, 

 boiled with silver nitrate as a catalyser and the resultant 

 permanganate estimated colorimetrically against known solu- 

 tions. The method is admittedly of no very high order of 

 precision, but it is quite accurate enough for the present pur- 

 pose, and for a preliminary survey its simplicity makes it 

 eminently suitable. In my hands o-oi mg. manganese 

 gives an obvious reaction and 0*005 m g- 1S detectable ; it is 

 inconvenient to have more than 2 or 3 milligrammes present. 



1 Jouy. Biological Chemistry, Vol. III. (1907), p. 151 ; Vol. VIII. (1910), 

 P. 237. 



2 E. M. Nance (Science Gossip, n.s. Vol. I\ . (1898), p. 343), showed 

 that the pink colour of the nacre of some specimens of Unio pictorum was 

 probably due to manganese. 



3 Journ. Biol. Chem., Vol. VIII. (1910), p. 237 ; H. P. Smith, Chemical 

 Xews, Vol. XC. (1904), p. 237 ; G. Bertrand and P. Thomas, Guide pour 



les manipulations de chimie biologique, ed. 2, 1913, pp. 16, 31. 



1917 Jan. 1. 



