69 

 ON THE OCCURRENCE OF MANGANESE 

 IN LAND AND FRESH WATER MOLLUSCA. 



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



(Continued from page 18). 



It is also noticeable that obvoluta, typically a beechwood 

 species, does not differ from the other helicids which evidently, 

 as a group, have very little manganese. B. ob scums gives 

 the same very high figure, whether from beechwood or from 

 a civilised hedge-bank between a high road and arable country. 



That snails eat manganiferous food is evident from the 

 analyses of their excreta — 



As far as these few results go, they indicate that the amount 

 of manganese in the body is not proportional to the amount in 

 the food. 



I fancy, therefore, that two factors are at work. In the 

 first place, there is the tendency for some species to accumulate 

 manganese from almost any surroundings, 1 and in the second 

 place, there is the influence of varying local conditions. The 

 relative import of these two factors can only be determined by 

 detailed investigation in a variety of localities and habitats 

 in different parts of the country ; at the moment it certainly 

 appears that the former commonly overides the latter. 



For there should be no great difficulty in any snail finding 

 as much manganese as it wants about the world. Manganese 

 in smaller or larger quantities is widely distributed both in 

 animals and plants as well as in inorganic nature. 2 Thus, it 



1 The carnivorous marine gastropod Sycotypus canaliculatus accumu- 

 lates zinc in considerable quantities from almost zincless surroundings 

 (L. B. Mendel and H. C. Bradley, Amer. J. Physiol., XIII. (1905), p. 17, 



xiv. (1905), p. 313)- 



2 According to F. W. Clarke (Data of Geochemistry, ed. 3, 1916, p. 34), 

 manganese constitutes 8 parts per ten thousand (0-08 per cent.) of all 

 known terrestrial matter, i.e. a good deal more than such well-known 

 elements as copper, lead, zinc or arsenic : like some rare elements (e.g. 

 gallium) it is widely dispersed. 



Naturalist, 



