In the year 1800, the majority of persons over twenty years old were more or less pitted by small-pox, being the survivors of a much greater number who had suffered from this disease. Dr. Miller in New York had just received from England a thread which had been steeped in the newly discovered vaccine matter, and was about to begin vaccination in this city. To-day there are many physicians who have never seen a case of small-pox, and a face pitted with the marks of this disease is rarely seen.
During the century there have appeared in civilized countries two strange and unfamiliar forms of epidemic disease, namely, Asiatic cholera and the plague, the first coming from the valley of the Ganges, the second from the valley of the Euphrates, and each having a long history. A really new disease was the outbreak in Paris in 1892 of a specific contagious disease transmitted from sick parrots, and known as psittacosis. This little epidemic affected forty-nine persons, and caused sixteen deaths. Typhus fever has almost disappeared, while some diseases have increased in relative frequency, in part, at least, because of medical progress. The children who would have died of small-pox in the eighteenth century now live to be affected with diphtheria or scarlet fever, and the increase in the number of deaths reported as due to cancer is partly due to the fact that a greater proportion of people live to the age most subject to this disease.
A large part of modern progress in medicine is due to improved methods of diagnosis, and to the use of instruments of precision for recording the results of examinations. The use of the clinical thermometer has effected a revolution in medical practice. Our knowledge of diseases of the heart and lungs has been greatly expanded during the century by auscultation [trained listening to sounds] and percussion, and especially by the use of the stethoscope. The test-tube and the microscope warn us of kidney troubles which formerly would not have been suspected, and the mysterious Röntgen rays are called in to aid the surgeon in locating foreign bodies and in determining the precise nature of certain injuries of the bones. Bacteriological examination has become a necessary part of the examination in cases of suspected diphtheria, tuberculosis, or typhoid, and a minute drop of blood under the microscope may furnish data which will enable the skilled physician to predict the result in certain cases of anæmia [bloodlessness], or to make a positive diagnosis as between malaria and other obscure forms of periodic fever.