Lead is peculiarly a cumulative poison, and post-mortem analyses of viscera show that it may be stored up in certain parts of the body, more especially in the bone and red bone marrow and brain, and to some extent in the liver, spleen, and kidneys. Any circumstance, therefore, that temporarily interferes with the ordinary channels through which lead is excreted may determine the presence of a much larger quantity than usual of the metal in circulation in the body; and if in addition an increased quantity of the poison be inhaled, more or less acute symptoms follow. The localization of the deposit of lead is therefore of some importance.
Meillère and Richer[4] give an analysis of various organs of the body, but their results are not in accord with the majority of other observers. They found that the hair particularly contains a large quantity of lead. They do not seem to have examined the bones. Next to the hair, the liver seems to have contained the largest amount. Wynter Blyth[5] found 117·1 milligrammes of lead in the brain of a person who died of encephalopathy. In another case he found 0·6 gramme in the liver, 0·003 in the kidney, and 0·072 in the brain. Hougounencq[6] examined the organs of a person who died from lead poisoning, and found the largest amount of lead in the large intestine.
| Large intestine | 0·2150 | gramme. |
| Small intestine | 0·0430 | „ |
| Liver | 0·0050 | „ |
| Brain | 0·0008 | „ |
In the lung, stomach, kidney, and heart, only traces were found.
Dixon Mann[7] describes some experiments in which potassium iodide was given in cases of chronic poisoning, and during the whole of the experiments the fæces and urine were analyzed three times a week. He found by this means that a considerable amount of lead was being eliminated by the intestine. He therefore administered 2 grammes of lead acetate three times a day for five days to a patient, and he found that the fæces contained 0·1762 gramme the first day, 0·17411 gramme the second day; the fourth day it had fallen to 0·0053 gramme, and on the sixth day to 0·0006 gramme. The largest amount at any one time in a day obtained from the urine was only just over 0·001 gramme; the average amount found in the case of chronic poisoning was about 3 milligrammes, whereas the greatest amount at any one time in the urine was only 0·9 milligramme.
The quantity of lead present in the brain necessary to determine acute poisoning is not known, and it is probable that an extremely minute quantity will produce very serious effects; and in support of this may be quoted a number of observations in which search has been made for the metal in persons who have died of diseases affecting the brain associated with other symptoms of poisoning, and yet post-mortem examination of the brain by chemical methods has not revealed the presence of any lead whatever. In the case reported by Mott (see [p. 71]), no lead at all was recognized in the brain.
There are no reasons, therefore, for supposing that the immunity to lead poisoning depends on the fixation and storing up of the poisonous metal in a non-poisonous form in some special situation in the body, and, further, the particular situation in the body richest in lead in any given case of poisoning will depend rather on (1) the type of compound causing the poisoning, and (2) the portal through which such poisoning occurs.
The question of the detection of lead in the body is referred to in the [chapter] dealing with Chemical Examination. It is as well to point out in this connection that chemical investigation of the amount of lead present in the organs of persons dying from lead poisoning should, if possible, always be made where there is any doubt as to the diagnosis.
Certain observers—amongst them Gautier[8]—are of opinion that traces of lead may be found in normal persons. Thus, in a rat (Mus decumanus) Gautier found 2 milligrammes of lead in 60 grammes of liver. He considers that in many persons at least 0·5 milligramme of lead may be swallowed daily incorporated with the food, as a number of foods are liable to contamination by lead. Tinned foods, particularly those which are soldered up after the materials have been placed in the tin, certain tinned fruits with acid juices, often contain small masses of solder loose in the tins; in the case particularly of fruits the natural acid may slowly dissolve the lead from the solder. The amount of so-called “normal” lead, if it is to be found at all, must be very small, and would certainly be much smaller in the case of a normal person than in one who had been subject to definite lead poisoning. Such experimental evidence as is forthcoming supports the clinical observations that persons exposed to small doses of lead eventually develop tolerance of the metal, so that they may ultimately withstand many times the dose sufficient in the first instance to produce poisoning.
Such circumstances are the natural factors in the prevention of poisoning, and if due care be given to their significance, the surgeon in charge of any lead works may by judicious treatment and alternation of employment so assist and strengthen the natural defensive forces that susceptibility may be diminished, and the degree of tolerance increased to a very considerable extent. We do not imply that efficiency in the exhaust ventilation can be in any way relaxed; all we desire to emphasize is that certain natural defensive forces of the body do undoubtedly exist by which susceptible persons ultimately become less susceptible, and that by appropriate means these defensive forces may be augmented.