have even a privy attached to them, and the feces are distributed in the vicinity of the houses.  This leads to contamination of the soil over wide areas.  Most of the inhabitants of the country go barefoot the greater part of the year, and this gives ready means of contact with the larvae which crawl over the surface of the ground.  The disease is necessarily associated with poverty and ignorance, the amount of blood is reduced to a low point, and industry, energy and ambition fall with the blood reduction; the schools are few and inefficient; the children are backward, for no child can learn whose brain cells receive but a small proportion of the necessary oxygen; and a general condition of apathy and hopelessness prevails in the effected communities.  The control of the disease depends upon the disinfection of the feces, or at least their disposal in some hygienic method, the wearing of shoes, and the better education of the people, all of which conditions seem almost hopeless of attainment.  The infection is also extended by means of the negroes who harbor the parasite, but who have acquired a high degree of immunity to its effects and whose hygienic habits are even worse than those of the whites.  The organism was probably imported with the negroes from Africa and is one of the legacies of slavery.

The diseases of animals are in many ways closely linked with those of man.  In the case of the larger parasites, such as the tapeworms and the trichina, there is a direct interchange of disease with animals, certain phases of the life cycle of the organisms are passed in man and others in various of the domestic animals.  A small inconspicuous tapeworm inhabits the intestine of dogs and seems to produce no ill effects.  The eggs are passed from the dog, taken into man, and result in the formation of large cystic tumors which not infrequently cause death.  Where the companionship between dog and man is very close, as in Iceland, the cases are numerous.

Most of the diseases in animals caused by bacteria and protozoa are not transmitted to man, but there is a conspicuous exception.  Plague is now recognized as essentially an animal disease affecting rats and other small rodents, and from these the disease from time to time makes excursions to the human family with dire results.  The greatest epidemics of which we have any knowledge are of plague.  In the time of Justinian, 542 B.C., a great epidemic of plague extended over what was then regarded as the inhabited earth.  This pandemic lasted for fifty years, the disease disappeared and appeared again in many places and caused frightful destruction of life.  Cities were depopulated, the land in many places reverted to a wilderness, and the works of man disappeared.  The actual mortality cannot be known, but has been estimated at fifty millions.  Plague played a large part in the epidemics of the Middle Ages.  An epidemic started in 1346 and had as great an extension as the Justinian plague, destroying