MODERN AGENTS FOR ANESTHESIA.

The original chemical bodies, nitrous oxide gas and sulphuric ether, have, notwithstanding much opposition and many advancements of rivals, retained a certain fair position as anæsthetics. Nitrous oxide, indeed, has of late been greatly extolled and raised into fervour of favour by the members of the Dental profession. Ether has been persistently employed in some parts of America and some parts of France, and its friends have quite recently claimed for it that it has not been the cause of one single death.

It is right that the members of the public, who, in common parlance, know only that sometimes they or theirs may have to be put "under chloroform," should know these and all other facts correctly, and intelligently; should know what agents are used and the relative value of each agent in respect to practicability of administration, certainty of action, and freedom from risk. I will essay, therefore, to bring these points clearly forward, not hurriedly and not with such exceeding brevity as to lose myself in obscurity.

Of the various agents that may fairly come under consideration, I will confine what has to be said, in the first instance, to substances which produce general insensibility, and of these I will name none that have not been tried, and for some valid reason or other been found wanting in some essential quality.

Nitrous oxide and sulphuric ether, in their respective ways, represent what are considered to be the physical requirements of agents for the production of anæsthetic sleep. The idea now is well nigh universal, that the agent must either be a gas, as nitrous oxide is, or a liquid very easily transformable into vapour, as ether is. These, I say, are conceded points, and are based on the belief that the best and readiest mode of producing the general sleep of insensibility, is letting the narcotic enter the system by the channel of the lung; by presenting to the blood as it flows over the lung from the right to the left side of the heart, some substance which the blood will absorb and will carry direct to the nervous centres in quick and steady stream. It is true we can produce the effect we want in another way, by another mode of entrance. For example, I have recently found it quite possible and easy to put an animal profoundly under chloroform, by inserting that substance, in its fluid state, beneath the skin with a fine needle, and this method could be applied to any soluble narcotic; but as a general principle, it is not so good a method as that of administering by what is called "inhalation."

We may put, therefore, in classification all the modern agent

we employ under two general heads, of GASES and VOLATILE FLUIDS, and I will set the most reliable substances in this order, adding to the name of each substance its chemical composition and physical characteristics.

I might expand these tables very largely. To the gases I might add carburetted hydrogen, light and heavy; carbonic acid, carbonic oxide, and hydrogen gas. To the liquids I might add methylic alcohol, chloride of ethyl, hydride of amyl, amylene, and many others, not omitting turpentine, which, at a push, has actually been administered successfully to the human subject. It is better to take simple types of those agents which are most direct in action, or most in use at this hour. Respecting those agents noted in our tables, it may be well to say of them at once, that, although they are the best up to the present time discovered, not one of them is to be considered perfect. All the gases are faulty because, being gases, they are practically unmanageable for ordinary application. Nitrous oxide gas, moreover, although it produces insensibility, causes, at the same time, darkening of the arterial blood, painfully rapid breathing, a countenance terrible to behold, and imminent approach to death. The liquids, on their side, are practical for administration, but more or less faulty in action.

At a future day, keeping to the same text, I will endeavour to point out the relative advantages and disadvantages of each of these agents in detail; and will try to explain what is wanted in an anæsthetic agent to make it in all respects perfect; and when I say perfect, I mean so perfect, that the removal of sensibility, and thereby the prevention of suffering by it, shall be attended with no anxiety, and with no sign or symptom that shall excite in the operator and administrator the anxiety which every administration, hitherto, has called forth.

THE DEPOSITS OF THE ATLANTIC IN DEEP WATER, AND THEIR RELATION TO THE WHITE CHALK OF THE CRETACEOUS PERIOD.

BY PROFESSOR D. T. ANSTED, M.A., F.R.S., FOR. SEC. G.S., &c.

[PLATE LV.]

THE origin of chalk, a substance very different from other limestones with which it agrees nearly enough in chemical composition, has always been a subject of enquiry with geologists, and the theories suggested have been numerous and varied. It was not till a necessity arose for determining the depth of the sea bottom across the Atlantic, preparatory to laying the cable for the Atlantic telegraph, that deep soundings were systematically taken between Europe and America; but when this was done a close relation was detected, both in appearance and organic contents, between chalk and the mud dredged up from the Atlantic bottom in deep water. Something like evidence has thus been obtained as to the possible conditions of deposit of the upper member of the cretaceous series.

White chalk is singularly uniform as a rock in all those parts of the world where it has been discovered. It is not always of the same degree of hardness, and it occasionally differs in colour as well as texture from the white chalk of the south of England that may be regarded as the type, but it is everywhere a homogeneous fine-grained rock showing few or no marks of stratification except on a large scale, and containing in comparison with many other rocks few organic remains of sufficient magnitude to be seen by the unassisted eye. It ranges from the north of Ireland in the north-west to the Crimea in the south-east, a distance of nearly 1,400 miles; and from the south of Sweden in the north almost as far as the Pyrenees in the south, a distance of nearly 1,000 miles. In England it approaches 1,000 feet in thickness, and in southern Russia it is as much as 600 feet. Throughout this wide space it retains its essential character as a rock, and cannot readily be mistaken