The principles of isolation as applied to a single case as indicated above may also be applied to infected localities in case of epidemics. When taken in time, all diseases which depend upon particulate contagia for their origin can be stamped out by isolation and disinfection. Unfortunately, to effect this promptly and successfully requires money, labor, and the co-operation of the well in the vicinity; which last it is usually impossible to obtain voluntarily or to compel sufficiently to secure the desired results. A question which sometimes arises in case of epidemics, and with regard to the necessity for which physicians will be consulted, relates to the closure of the public schools. It is certain that the assemblage of children in schools exerts a powerful influence on the spread of such diseases as scarlet fever, diphtheria, and whooping cough. On the other hand, the closure of the schools infringes upon the rights of a large number of the community, and if long continued, as it sometimes must be to be really efficacious, inflicts upon them {204} a permanent loss. It is, moreover, a confession on the part of the authorities of inability to induce or compel what must always be a comparatively small part of the community to take the proper precautions. It is never justifiable to close schools on account of small-pox, and where there is a competent health authority supported by the influence of the medical profession, it must be a very exceptional set of circumstances which justifies their closure for diphtheria or scarlatina. It is not deemed expedient here to discuss the vexed question of quarantine. It is more important against yellow fever than any other disease, because every day of delay of the entrance of the disease which it secures lessens largely the subsequent mortality, since the duration of the disease is limited by frost. This is not the case with cholera, and the mere keeping this disease out of a place for a few weeks does not diminish its ravages when it has once gained an entrance. To rely altogether on quarantine, either maritime or inland, to keep yellow fever, cholera, or any other disease out of this country is a far greater mistake than to neglect it altogether. The practical way to isolate and quarantine is to get as close to the affected spot as possible. Precautions at Havana for yellow fever, or at Hamburg for cholera, are far more useful to the United States than the same amount of work at our own ports can possibly be; really good work in this direction must be not only national, but international.