common microscope glass. When the vapour had been thus directed for three minutes, the glass was gently dried. As the drying proceeded, a fine white cloud became visible on the part of the glass forming the cell. The microscope revealed the presence of a field of the crystals of chloride of ammonium, which are here shewn. They are a fair representation of those formed from blood-vapour.

EXPERIMENT CCCIII. Formation of Chloride of Ammonium from Blood-Vapour. The process was performed on blood taken from an ox. The result was the same.

[EXPERIMENT CCCIV. Formation of Chloride of Ammonium from Blood-Vapour. A pint and a half of blood was drawn, in the open air, from the neck of a sheep into a bowl, and was briskly whipped with twigs. This gave rise to a more than ordinary evolution of vapour, in which I held a microscope glass moistened with hydrochloric acid. After four minutes, I dried the glass over a spirit lamp, and found it studded with groups of crystals as before. For comparison, another glass, also moistened with acid, was placed at the distance of eight yards from the blood; this, on being dried, yielded no evidence whatever of crystals.

EXPERIMENT Cccv. Formation of Chloride of Ammonium from Blood-Vapour. One pint of fresh blood from a sheep was mixed with a pint of distilled water at 100° Fahr. There was a free and rapid evolution of vapour. The microscope glass, moistened with acid and held in this vapour, was dotted over its entire surface with the crystals.

When a microscope glass is simply held over bloodvapour in the air, the objection may be made that the ammonia comes from the air itself; and, although this

objection is met by the precautions given above, it may be removed still better by excluding the air altogether, as in the succeeding plans.]

One very simple plan consists in the use of a glass vase, of the kind used for " potichomania". This holds a large quantity of blood, and offers a wide surface for evaporation. Into the hollow cover of the vase is inserted a movable wooden shelf, to the under surface of which a microscope glass is attached by India rubber bands. The vase having been filled with freshly drawn blood, and the under surface of the microscope glass having been moistened with hydrochloric acid, the cover, made air-tight by a few bands of India rubber, is immediately put on. The ammonia arising from the blood combines with the hydrochloric acid, and leaves chloride of ammonium distributed over the glass. In my first experiments, I chiefly used the apparatus above described, and obtained crystals of chloride of ammonium from the blood of various animals-heifers, bullocks, and sheep especially, not once failing in twenty-five consecutive experiments.

[EXPERIMENT CCCVI. Copious Deposition of Chloride of Ammonium from Sheep's Blood. A sheep was one day killed, which was evidently in an enfeebled state, either from disease or from over fatigue. I should presume from fatigue; for there was no manifest organic disease on inspection. A pint of blood was drawn from this animal into the potichomania jar, and the lid with the acidified microscope glass was put on. On gentle evaporation, the most copious deposit of the chloride I have ever seen, formed on the glass, which was, indeed, frosted over its entire surface. The blood in this instance was fully five minutes coagulating, a period extraordinarily long in regard to sheep's blood.

I afterwards made an instrument of another kind, as depicted in the drawing. A pint bottle (D), with a well fitting cork, has a tube

(c) inserted through the cork. The upper part of the tube is blocked for supporting a small glass cylinder (B) lying horizontally across it. The glass cylinder is perforated in its centre with a hole through which the upright glass tube passes. The cylinder is closed at one end; and the other is fitted with a stopper. When it is to be used, a microscope glass (A), moistened with hydrochloric acid, is placed, as

C

indicated, in the cylinder, the acidified surface downwards over the tube.

EXPERIMENT CCCVII. Formation of Chloride of Ammonium from Blood-Vapour. I received half a pint of blood from the neck of a sheep into the bottle (D); then inserted the cork with the tube (c), and the cylinder containing the microscope glass and acid. The blood coagulated in two minutes; but the bottle was allowed to stand for half an hour. Then the cylinder (B) was removed, and placed under a bell-jar over sulphuric acid in a sandbath at 100° Fahr. When the microscope glass, thus dried, was removed, it was found, as before, dotted over with crystals of chloride of ammonium.

In these days of no blood-letting, it is a difficult thing to obtain human blood in quantity for the purpose of experiment. However, through the kindness of Mr.

Betts, cupper, of Wimpole Street, I have been enabled to perform, with the blood of the human subject, three experiments, which possess peculiar interest. I arranged for Mr. Betts a cupping-glass for experimental purposes. It was simply a straight cupping-glass, having stretched across it within in its middle part a short microscope glass, which was held in place by two slips of cork, its flat surfaces looking upwards and downwards. When the cup was to be used, two or three drops of hydrochloric acid were placed on the upper surface of the microscope glass: the scarifications were made in the patients, and the cup was applied.

EXPERIMENT CCCVIII. Ammonia evolved from Human Blood. Mr. Betts had a patient to cup, who was an old man, and who for many years had been cupped regularly once a month. He was thin, and sickly looking; but suffered from giddiness and affection of the head if the cupping were not performed. Mr. Betts arranged the glass as I had directed him, and, after scarifying, placed it on the back of the patient, and drew off about four ounces of blood. He then removed, emptied, and gently dried the cupping-glass, and at once brought it to me for examination. On the glass slide, there were a few crystals of chloride of ammonium: but, on looking at the upper and clean part of the cup, I observed there several groups of small white specks, on which, with a little trouble, I brought the microscope to bear. They resolved themselves into fine groups of chloride of ammonium crystals.

EXPERIMENT CCCIX. Ammonia evolved from Human Blood. A short time afterwards, Mr. Betts repeated the experiment on another patient, who was in the prime of life, and was bled to meet a plethora; for he who

takes in too much must have too much let out. The glass was applied, removed, and dried, as before. In this case, the microscope again revealed groups of the crystals, which, as in the previous instance, were not deposited on the slip which bore the acid, but on the upper part of the cupping-glass.

EXPERIMENT CCCX.

Ammonia evolved from Human Blood. On another occasion, Mr. Betts cupped the first mentioned patient; and was so good as to send for me to take part in the experiment. I arranged the glass myself. After the application, I saw distinctly in the glass the white curling fumes of chloride of ammonium, as the blood-vapour came into contact with the acid on the glass. This blood, unlike what generally occurs when cupping is performed, remained fluid, åfter the glass was removed, for full eight minutes. I held a microscope glass moistened with acid over the blood, gently dried it, as well as the cupping-glass and its contained slip, examined these, and again found the crystals, the greater number being in the upper part of the cupping-glass.

In these experiments, three points were satisfactorily established: 1. That the ammonia did not come from the air, inasmuch as the cupping-glass is not only closed, but partly vacuous; 2. That it did not come from the acid used, because it was the vapour of the acid which, combining with the ammonia, deposited the crystals in the upper part of the glass; 3. That human blood evolves ammonia.

Against the experiment, there is one disadvantage, which, indeed, applies to the preceding experiments; namely, that, as the fumes of chloride of ammonium are formed, they descend and are absorbed by the blood, so