CHAPTER I
VACCINATION AND SMALL-POX
Among the greatest self-created scourges of civilized humanity are the group of zymotic diseases, or those which arise from infection, and are believed to be due to the agency of minute organisms which rapidly increase in bodies offering favourable conditions, and often cause death. Such diseases are: plague, smallpox, measles, whooping-cough, yellow fever, typhus and enteric fevers, scarlet fever and diphtheria, and cholera. The conditions which especially favour these diseases are foul air and water, decaying organic matter, overcrowding, and other unwholesome surroundings, whence they have been termed "filth diseases." The most terrible and fatal of these—the plague—prevails only where people live under the very worst sanitary conditions as regards ventilation, water supply, and general cleanliness. Till about 250 years ago it was as common in England as small-pox has been during the present century, but a very partial and limited advance in healthy conditions of life entirely abolished it, its place being to some extent taken by small-pox, cholera, and fevers. The exact mode by which all these diseases spread is not known; cholera, typhus, and enteric fever are believed to be communicated through the dejecta from the patient contaminating drinking water. The other diseases are spread either by bodily contact or by transmission of germs through
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