_The determination of the reducing substances_ can be effected by Salkovski’s gravimetric method, but I prefer Moritz’s volumetric method, on account of its simplicity. For the experiment we prepare the following solutions: 1. A solution of sulphate of copper of 80.78 grammes Cu S O{4} + 5 H{2} O, in a litre; 2. Solution of caustic soda of 120 grammes Na H O, in a litre; 3. Watery solution of ammonia, of 7.1 per cent. N H{3}, specific gravity 0.9722. For conducting the volumetric analysis we place in one of Erlenmayer’s flasks, containing about 250 cubic centimetres, about 2 cubic centimetres each of the soda solution and the solution of sulphate of copper, and add 140 cubic centimetres of the ammonia solution. We thus obtain a dark blue fluid, which we now boil. During the boiling we allow the urine to be analyzed to flow in from a burette until the fluid becomes colorless. A table given by Moritz in the forty-sixth volume of the ‘_Archiv für klinische Medizin_,’ shows us in per cents. the quantity of reducing substances contained in the urine we have used. In conclusion we investigate the condition of metabolism by _determining the excreted nitrogen_. Nitrogen is excreted both by the urine and the fæces. The greater part is found in the urine, whilst, on the contrary, the quantity of nitrogen excreted in the fæces amounts to more than 1 gramme per day. If, then, we determine the quantity in the urine alone and add 0.94 gramme as a correction for the nitrogen excreted with the fæces, the resulting error will be unimportant. The best and at present most useful method of determining the nitrogen is that of Kjeldahl. I generally use it in my analyses as one that can be conveniently carried out. For this purpose we place 5 cubic centimetres of filtered urine in a long-necked flask, add about 3 decigrammes of yellow oxide of mercury and 10 cubic centimetres of chemically pure sulphuric acid. We then carefully warm the brownish-black mixture over the flame of a Bunsen burner until it has become colorless. We now allow it to cool. The mixture is now poured into an Erlenmayer flask containing three-quarters of a litre of water, is neutralized with 30 per cent. soda-lye, and then 40 cubic centimetres of a 4 per cent. solution of potassium sulphide is added. The whole is next subjected to distillation. Decinormal sulphuric acid contained in the receiver takes up the ammonia which distils over. The acid still remaining free after the completion of the distillation is titrated with decinormal caustic soda. As 1 cubic centimetre of decinormal sulphuric acid corresponds to 0.0014 gramme of nitrogen, we can easily reckon the quantity excreted daily. We know how much nitrogen is contained in 5 cubic centimetres of urine, and can easily find to how much the daily quantity amounts by multiplying by it and dividing by five.