In disinfecting the sick-room, the furniture, woodwork, and floor should first be scrubbed with carbolic soap and hot water or a solution of bichloride of mercury (1-500). The windows, ventilators, and fireplace should then be tightly closed and the fumes of burning sulphur or formaldehyde gas used to complete the disinfection. Sublimed sulphur burned in a moist atmosphere (one pound to every thousand cubic feet of space) is effective, but is at the same time objectionable on account of its tendency to bleach or discolor all textile fabrics. In well-furnished rooms, containing articles liable to be injured by sulphur or steam, such as wall-paper, paintings, books, etc., it is advisable to use, whenever possible, a formaldehyde gas-generator, which can usually be obtained from the local Board of Health. CHAPTER IV. VACCINATION. Vaccination consists in the inoculation of virus taken from the pock produced by vaccinia. *Vaccine Virus.*--Virus has been taken from vaccine vesicles on almost all animals susceptible to vaccinia, but throughout the greater part of the last century the material used in the vaccination of human subjects was taken generally from a vaccine vesicle on the arm of a previously unvaccinated healthy child. Such virus when collected at the proper time was found to take with great regularity, and vesicles resulting from its use were uniformly well developed and typical. Humanized virus was, however, open to the objection that it could communicate disease if the child were not perfectly healthy, and as a matter of fact it did communicate syphilis in a certain number of instances. The possibility of this infection was so serious an objection to the use of virus from this source that in the last quarter of the century calf virus, recommended and used in Italy many years before, was gradually substituted for human virus, and at the present time the use of animal virus is general in Europe and in the United States. In the production of virus, calves are for commercial reasons generally preferred to other animals. Calves take typically, and a large amount of virus can be collected from them, whereas all other animals either are comparatively expensive, or take poorly, or are able to furnish but little virus. Cows also are more expensive, are less easily handled, and develop vaccine vesicles less typically.