EXPLANATION OF PLATES.

PLATE I.

Fig. 1. Urea. Quadratic. prisms, and their combinations. The lower, more perfect crystals, are obtained by the addition of absolute alcohol to a saturated solution of urea in spirits of wine, The upper half of the circular field exhibits prisms and needles obtained by the rapid evaporation of a solution of urea in methyl-alcohol. (See p. 45.)

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2. Nitrate of urea. Rhombic prisms and plates, representing the type of a precipitate obtained by adding to a concentrated watery solution of urea, colourless nitric acid. Much more perfect crystals, radiary groups of needles, are obtained by the slow evaporation of a solution of this salt in water. (See p. 48.)

3. Oxalate of urea. Rhombic prisms and plates, representing the type of a precipitate, by adding oxalic acid to a solution of urea. (See p. 49.)

4. Nitrate of urea and mercury; the salt obtained by permitting the precipitate of Liebig's quantitative test to crystallize in the acid fluid. (See pp. 50, 53.)

5. Uric acid, pure, in delicate rhombic prisms and plates. They polarize in beautiful colours between crossed Nicholl prisms. (See p. 80.)

6. Uric acid, in rhombic prisms and plates, crystallized from concentrated hydrochloric acid. (See p. 80.)

PLATE II.

Fig. 1. Uric acid. A variety of forms of uric acid met with in spontaneous deposits. (See p. 80.)

2. Crystallized uric acid sediment mixed with blood-corpuscles, from the observation described at p. 107.

3. Deposit of urate of soda, described in the observation recorded at p. 101, et seq.

4. Hippuric acid. Microscopical rhombic prisms, single and in groups, from human urine. (See p. 143.)

5. Creatine. Clinorhombic prisms and plates. Though correct, this figure is not a very typical representation. (See pp. 117, 118.)

6. Creatinine. Clinorhombic prisms and plates, typical of a good specimen, crystallized from alcohol. (See p. 123.)