Chloroform and similar agents are termed “anæsthetics” because they abolish the irritability of the cortex of the great brain, before their effects upon other parts of the nervous system are sufficiently pronounced to endanger the working of the animal machine. Pain ceases to be felt before the dose of anæsthetic is sufficient to suspend the irritability of the centres of reflex action. All protoplasm, whether animal or vegetable, is susceptible to the influence of these agents. They cause it to enter into a state which resembles death in all respects save the impossibility of revival. There is a great demand in the Paris flower-market for white lilac in the winter. The plant cannot be forced until after a period of rest. By withholding water and placing the bushes in a cool, shady place, horticulturists endeavour to send them prematurely into their winter sleep. Recently it has been found that from three to four weeks can be gained by placing the bushes for a couple of days in an atmosphere charged with the vapour of ether. Some change of state is evidently produced in protoplasm by anæsthetics. It ceases to be capable of receiving or transmitting stimuli. But we cannot picture the change as being sufficiently pronounced to justify the hypothesis that so long as it is irritable protoplasm is a complex substance which is resolved, as it loses its irritability, into simpler compounds familiar to the chemist. Perhaps it would be more correct to say, we cannot picture these chemical substances as reuniting into protoplasm when the effect of the anæsthetic passes off. Rather are we driven to think of living matter as a mixture of many substances in a state of molecular interchange, and to suppose that the activity of this interchange is diminished by anæsthetics.