The estimation of the quantity of lead present in organic fluids, with the disturbing influence of the presence of other metals, is a factor which always complicates the use of the sulphuretted hydrogen colorimetric estimation. It is almost impossible, when dealing with fæces, with blood, or, on the other hand, with artificial digests containing bread and milk, to eliminate the disturbing influence of iron. Further, if steps are taken to remove the iron and other metals, so much loss takes place in the manipulations necessary that the results arrived at are not satisfactory. Whenever dealing with organic matter, such as urine and fæces, it is best to make a blank test with a similar quantity of the substance under examination obtained from other sources, and to subtract the error found due to iron, when a rather closer approximation may be arrived at. So far as can be estimated, the minimal quantity of lead required to produce poisoning is 0·005 gramme per kilogramme of body weight; but, on the other hand, persons who have swallowed much larger doses than this have exhibited no symptoms of poisoning. There is every reason to suppose that lead absorbed through the lung produces a maximum toxic effect, and, from the estimation of the quantity of lead found in the body after death, it is highly probable that exceedingly minute quantities of lead have, when absorbed over long periods, produced changes not only by their actual presence in the tissues, but also have set up degenerative changes which progress even after the elimination of the metal from its local position. =Histological Examination.=--In addition to the chemical examination of tissues from a person who has died of suspected lead poisoning, it is of the highest importance to make histological examinations, as the naked-eye appearance of post-mortem examination is frequently insufficient to give any clue to the cause of the poisoning. Moreover, in a large number of instances the necropsy may exhibit a number of signs of disease, such, for instance, as granular kidney, cirrhosis of the liver, and so forth, which are associated with diseases other than lead poisoning, and, in the absence of any present or past evidence of definite hæmorrhages found associated with the other lesions already mentioned, an ordinary autopsy must be inconclusive. It is true that such pathological conditions are consistent with poisoning by lead; and if the individual has been a lead-worker, it is easy, but frequently erroneous, to conclude that the symptoms owe their origin to the worker’s occupation. We are entirely in sympathy with the remarks of King Alcock[9], who says: