In 1898, Ronald Ross proved that the mosquito was responsible for spreading malaria. Although nitrous oxide, or laughing gas, had been proposed as an anaesthetic as far back as 1799 by Humphry Davy, it was not until 1846 when an American dentist named William Morton started using ether on his patients that anaesthetics became common in the medical profession. In 1847 chloroform was introduced as an anaesthetic by James Young Simpson. Chloroform was favoured by doctors and hospital staff because it is much less flammable than ether, but critics complained that it could cause the patient to have a heart attack. Chloroform gained in popularity in England and Germany after John Snow gave Queen Victoria chloroform for the birth of her eighth child (Prince Leopold). By 1920, chloroform was used in 80 to 95% of all narcoses performed in the UK and German-speaking countries. A combination of antiseptics and anaesthetics helped surgeons operate more carefully and comfortably on their patients. Anaesthetics made painless dentistry possible. At the same time sugar consumption in the British diet increased, greatly increasing instances of tooth decay. As a result, more and more people were having teeth extracted and needing dentures. This gave rise to "Waterloo Teeth", which were real human teeth set into hand-carved pieces of ivory from hippopotamus or walrus jaws. The teeth were obtained from executed criminals, victims of battlefields, from grave-robbers, and were even bought directly from the desperately impoverished. The increase in tooth decay also brought the first prominent recommendation for fluoride as a nutrient, particularly in pregnancy and childhood, in 1892. News of the discovery of X-rays in 1895 spread like wildfire. Its medical value was realised immediately, and within a year, doctors were prescribing X-rays for diagnosis, in particular to locate bone fractures and foreign objects inside the patient's body. Radioactivity was discovered 1896, and was later to used to treat cancer. During the second half of the nineteenth century, British medical doctors became increasingly specialised, following the footsteps of their German counterparts, and more hospitals were built. Surgeons began wearing gowns in the operating room and doctors white coats and stethoscopes, sights that are common in the early twenty-first century. Yet despite all the aforementioned medical advances, the mortality rate fell only marginally, from 20.8 per thousand in 1850 to 18.2 by the end of the century. Urbanisation aided the spread of diseases and squalid living conditions