PROF. ATTFIELD POISOXS NOT ALWAYS POTSONS. 151 



I think the iutcresting point here is, the illustration afforded to 

 the fact that a substance which is a virulent poison to one animal 

 may be the food of another. That of course brings to our minds the 

 allied truth, that poisons, such, for instance, as tobacco or opium, 

 if used and persisted in for a length of time, can be borne by the 

 human system pretty easily. I do not want to be hard on tobacco, 

 because I am not a smoker myself and therefore possibly preju- 

 diced. And I need not remind you what an enormous quantity of 

 laudanum and other equally poisonous opiates are taken by indi- 

 viduals who have accustomed themselves to the use of such drugs. 

 I have seen more than one or two persons drink off a wineglassful 

 of laudanum and be none the worse : indeed, much the better, — 

 for whereas they came into the room trembling, with hands 

 shaking violently, a few minutes after they had taken their glass 

 they became quite calm and got into their normally, or rather 

 abnormally, quiet condition. Many animals are known to eat 

 poisonous substances, and apparently enjoy and thrive upon them — 

 vegetable substances, I mean, well known to be poisonous to man. 



Soon after I had published among a few scientific friends a 

 short paper on the subject of these mites, several persons kindly 

 wrote to me and drew my attention to cases where, following my 

 hints, they had found mites and such things living on poisonous 

 substances. Mr. Hart, of Keyworth, sent me some mites that he 

 found quite at home on extract of camomile, a very bitter 

 substance ; Mr. Baldock, now of Norwood, some living on extract 

 of hemlock, and some on extract of belladonna; Mr. Jackson, of 

 Crediton, some on extract of lettuce. I took the trouble to prove 

 by experiment that there was plenty of the respective poisons in 

 the extracts, and that the animals throve well on their food. One 

 friend, Mr. Whipple, drew my attention to a most astounding case. 

 I think I had better read the account to you, and then you can 

 take it for what it is worth. I could scarcely believe it myself. 

 One must hesitate, however, before coming to conclusions on 

 matters of this kind. The poison mentioned is sulphate of zinc. 

 Now sulphate of zinc is a mineral poison. Hitherto I have been 

 speaking of poisons other than mineral. Although salt is a mineral, 

 and although much of our food contains a little mineral matter, yet, 

 on the whole, animal and vegetable matter forms our true food ; 

 mineral matter alone, noxious or non-noxious, is scarcely food. 

 The account is by a Mr. Holt, and originally appeared in the 

 'Annals of Philosophy' for December, 1818, vol. xiv, p. 454: it 

 is reprinted in the ' Pharmaceutical Journal ' for April, 1862. 



" A few months since, having occasion for some sulphate of zinc, I proceeded 

 to examine ray collection of metallic salts, amongst which I expected to find what 

 I required. I readily found the paper, in which the label informed me the sul- 

 phate of zinc had been ; but was much surprised to find none in it. A consider- 

 able quantity of mimite particles of a yellowish-brown substance were scattered 

 through the paper, some adhering to it, and all held together by an extremely 

 fine silky thread. On removing the various papers, and searching to the bottom 

 of the box, I discovered a portion of the sulphate of zinc, enveloped in a heap of 

 the powdery substance. When I took it up a very large spider ran out of it, and 



