This section is from the book "Dental Medicine. A Manual Of Dental Materia Medica And Therapeutics", by Ferdinand J. S. Gorgas. Also available from Amazon: Dental Medicine.
Methylene is obtained by the action on chloroform of nascent hydrogen. It boils at 1040 F. and 400 C, and is a colorless, volatile liquid with the odor of chloroform. It was introduced in 1840 by Dr. B. W. Richardson. It is pleasant to inhale in the form of vapor. Its specific gravity is 1.344, and evaporates more easily than chloroform, and, the vapor being denser, it requires a less quantity than ether. It is soluble in alcohol and ether, and is frequently combined with other agents to lessen its cost.
Methylene possesses many of the dangerous qualities of chloroform when used as a general anaesthetic, and death results from syncope with dilated pupils. It was a favorite anaesthetic with Dr. Richardson, and Sir Spencer Wells believes that it has all the advantages of complete anaesthesia with fewer drawbacks than any other. He gives it diluted with air by Junker's apparatus, and it is supposed that he employs a mixture of methylic alcohol and chloroform.
Despite the fact that so eminent a surgeon as Sir T. Spencer Wells uses methylene as an anaesthetic, and has continued to advocate its use for twenty years, very few have followed his example. This is because the statistics of mortality from this anaesthetic apparently show it to be considerably more dangerous than ether. Like chloroform it destroys life by its effects upon the heart.