ODF ANAESTHETICS 155 
to keep a patient under the influence of the gas for a protracted period. It is 
questionable, however, whether nitrous oxide, if employed for producing long- 
continued insensibility, would prove as safe as chloroform, and it is pretty 
generally admitted that its legitimate place is for operations of very short dura- 
tion. But for avoiding the brief but acute agony of tooth-extraction it appears 
to be an unquestionable boon to humanity. 
The benumbing influence of cold was brought into requisition several years 
ago by Dr. James Arnott for producing local anaesthesia, by means of a freezing 
mixture of pounded ice and common salt.1_ The same object has since been 
more efficiently attained by Dr. B. W. Richardson, by ingeniously availing 
himself of the reduction of temperature occasioned by evaporation. Anhydrous 
sulphuric ether intimately mingled with air in the form of spray is projected 
upon the part by means of a suitable apparatus easily worked by the hand. 
In a few seconds the skin upon which the spray plays suddenly assumes a snow- 
white colour, implying that its surface is completely frozen. It is well to con- 
tinue the application for a little while after this change has occurred, in order 
to ensure the penetration of the effect to a sufficient depth. The frozen parts 
may then be incised or operated on in any way that may be desirable, without 
the slightest pain to the patient, and the tissues when thawed are generally as 
well disposed for healing as usual. 
This method is necessarily of limited application. It is only adapted for 
superficial operations, and even for many of these the rigidity of the tissues 
occasioned by congelation is inconsistent with efficiency of performance, as in 
removing epithelial cancers, where the sense of touch is the principal guide for 
the surgeon ; or, again, in taking away thin-walled atheromatous cysts, where 
looseness of the surrounding cellular tissue is essential to satisfactory dissection. 
Nevertheless there are many cases, such as the incising of a boil or the removal 
of the nail of the great toe, in which this means of producing local anaesthesia 
proves perfectly satisfactory. In operating on the extremities I have found 
great advantage from restraining the circulation with a tourniquet, so as to 
prevent the oozing of hot blood, which would otherwise interfere with maintain- 
ing the frozen condition or extending it to deeper parts. 
ParT III. WRITTEN 1882 
Since Part II of this article was written, twelve years ago, ether, on account 
of its supposed greater safety, has to a large extent superseded chloroform 
in the practice of many British surgeons. At the same time the manner of 
1 See Lancet, October 30, 1858. 
