From the result of his investigations Grünbaum points out that these reactions must be looked upon rather as “special” than “specific,” in view of the fact that his “chimpanzee antiserum” gave a _slight_ but distinct turbidity after a few hours with horse blood. He also suggests a method for the microscopical application of the “biological test,” by using a 1 per cent. blood solution with a drop of “antiserum.” This method has enabled him to distinguish between human and anthropoid blood, the reaction occurring earlier and being more complete when the “antiserum” is used on its own blood. Vegetable and other Stains which resemble Blood Certain vegetable colouring matters give spectra which may be mistaken for blood, from their close similarity. Of these cochineal dissolved in a solution of alum gives two bands similar to O₂Hb. On the addition of boric acid the bands move to the violet end of the spectrum, but they are unaffected if the colouring matter be blood. Lac-dye, alkanet root, madder, and others also give spectra resembling O₂Hb, but they are changed or disappear on adding ammonia or sulphite of potassium, while the spectrum of blood remains unaltered. As stated previously, spectra of colouring matters other than blood are not capable of being altered by reducing agents, so that, however similar they may be to O₂Hb, they cannot be accepted as derived from blood unless the spectra of reduced Hb and reduced hæmatin can be obtained in the way described. Cochineal, colours of certain roots and wood, turn crimson on the addition of ammonia, logwood bluish-black. The colour of the rose and certain flowers turn green on adding ammonia. Fruit-stains from mulberry, currants, gooseberries, &c., turn bluish-green with ammonia. Vegetable stains have their colour heightened by the action of dilute acids. Chlorine bleaches fruit-stains, but turns the colour of blood-stains to an olive-green. Red dyes fixed by a mordant are not influenced by ammonia. Iron stains are usually blackened by ammonium sulphide. Red paint may contain red oxide of iron; digest with hydrochloric acid and test for iron, by adding ferrocyanide of potassium to obtain the Prussian blue. Iron stains may be of a reddish-brown or orange colour, and insoluble in water, so that HCl is used to dissolve them. _Citrate and malate of iron_ stains are soluble in water; the addition of ammonia to an aqueous solution produces no change; guaiacum will give a blue reaction if a persalt of iron be present. The addition of hydrochloric acid and ferrocyanide of potassium will give the Prussian blue reaction. A drop of nitric acid added to the solution will oxidise the iron to the ferric state, and on the addition of a few drops of fresh-made aqueous solution of sulphocyanide of potassium the port-wine colour of sulphocyanide of iron will be produced. A control test must be made with distilled water to prove the purity of the reagents, and the two results compared with each other.