This test is said to give a reaction in the presence of 0·00003 gramme. _Determination of Lead in the Urine._--The quantity of lead passed by the kidneys into the urine is always small, even in acute lead poisoning. Further, the lead is excreted in organic combination, and is therefore difficult to detect. For absolute quantitative examination it is essential to evaporate the whole bulk, using at least ¹⁄₂ gallon of the fluid, and proceeding with the concentrate in the manner indicated in the estimation of lead. For the qualitative examination many methods have been suggested, but all of them are more or less fallacious. In certain instances in acute lead poisoning, or where a relatively large quantity of lead is excreted by the kidney, acidulation of the fluid with strong sulphuric acid direct will at times produce a precipitate of lead sulphate, which may be filtered off and the filtrate examined by the usual tests--namely: A white precipitate with dilute sulphuric acid. A yellow precipitate with potassium chromate, hardly soluble in nitric acid, but soluble in alkalies. A blue flame on heating on a platinum wire, and finally, if sufficient substance is present, the reduction to metallic form with the blowpipe flame. A method has been recommended of suspending a small bag of calcium sulphide in the sample to be examined, the supposition being that, if the calcium sulphide in the bag showed blackening, it would be due necessarily to lead. This is highly questionable, and in the hands of one of us (K. W. G.) has not given satisfactory results. A further method, which is quite simple in application, and occasionally gives confirmatory results, may be applied in the following manner: The urine to be examined is inoculated with the _Bacillus coli communis_. For this purpose a small quantity of fæces may be used. The _B. coli_ in its growth makes use of the organic substances in the urine, and at the same time sets free sulphuretted hydrogen. The urine left is filtered, the filtrate dissolved in 10 per cent. nitric acid (minimal quantity), and the filtrate examined by the usual tests. This method has occasionally given quite good results in the hands of one of us (K. W. G.), and is, moreover, an exceedingly easy one to carry out. Passing sulphuretted hydrogen direct through the fluid is of no value, as it is necessary first of all to split up the organic compound before it will react to sulphuretted hydrogen. _Electro-Chemical Methods._--Of all the methods at present in use for the estimation of the presence of lead in the urine, the electro-chemical gives by far the most satisfactory results. Several methods are described: The first method consists in using magnesium, which is left for some hours in the urine, which has been previously strongly acidulated. In this manner Marsden and Abram[2] say that they have been able to detect 1 part in 50,000 in the urine without difficulty. The method adopted is as follows: