602 DR DAVY’S OBSERVATIONS ON FISH, 
‘*confirmed phthisis and of hemoptysis, the probable result of tuberculosis,” 
entered in the register of the Dispensary, 234 males, 376. females, whose ages and 
occupations are given individually, the small number of four only were of fisher- 
men’s families,—one male and three females,—which is in the ratio of one to 
163°2; and of watermen ‘“ who fish with hook and line, when other work is 
scarce, generally very poor, and of habits generally by no means temperate or 
regular,” the number, including their families, did not exceed eleven, of whom 
ten were males, one a female, which is in the ratio of one to 58°8. The entries 
from which the 654 cases are extracted, Dr Cookworrtnuy states, exceed 20,000. 
He assures me, that had he taken scrofula in all its forms, the result would, he 
believes, have been more conclusive. 
Such a degree of exemption as this return indicates in the instances of fisher- 
men and boatmen, is certainly very remarkable, and deserving of attention, espe- 
cially considering the prevalency of tubercular consumption, not only in the work- 
ing classes generally throughout the United Kingdom, but also amongst the regular 
troops, whether serving at home or abroad, and having an allowance of meat 
daily, but rarely tasting fish.* 
If the exemption be mainly owing to diet, and that a fish diet, it may be 
presumed that there enters into the composition of fish, some element not common 
to other kinds of food, whether animal or vegetable. This I believe is the case, 
and that the peculiar element is iodine. 
I may briefly mention, that in every instance in which I have sought for this 
substance in sea-fish, I have found distinct traces of it, and also, though not so 
strongly marked, in the migratory fish, but not in fresh-water fish. The trials I have 
hitherto made have been limited to the following, viz., the Red Gurnet, Mackerel, 
Haddock, Common Cod, Whiting, Sole, Ling, Herring, Pilchard, Salmon, Sea-Trout, 
Smelt, and Trout. In each instance, from about a quarter a pound to a pound of fish 
was dried and charred, lixiviated, and reduced to ashes, which were again washed. 
From the sea-fish, the washings of the charcoal afforded a good deal of saline 
matter on evaporation; the washings of the ash less. The saline matter from 
both consisted principally of common salt, had a pretty strong alkaline reaction, 
and with starch and aqua regia. afforded, by the blue hue produced, clear proof 
of the presence of iodine. In the instance of the fresh-run Salmon, Sea-Trout, 
and Smelt, a slight trace of iodine was thus detected; in the spent Salmon de- 
scending to the sea, only a just perceptible trace of it was observable, and not a 
trace of it either in the Parr or in the Trout. 
That iodine should enter into the composition of sea-fish, is no more perhaps 
than might be expected, considering that it forms a part of so many of the inhabi- 
* In 1205 fatal cases, not selected, in which the lungs were examined at the General Hospital, 
Fort Pitt, Chatham, tubercles were found to exist in 734 (61-7 per cent.) See the author’s “ Notes 
on the Ionian Islands and Malta,” vol. ii., p. 312, for details. 
