"The causes which affect human health are often obscure, many of them so subtile that they are discerned with difficulty, and can only be appreciated by those who devote their time to the study and observation of them through all their changes. They even sometimes escape the keenest observation of the most accurate observers; yet it is reasonable to suppose that those who prosecute such investigations with zeal actually make some progress in knowledge; and if any discovery of knowledge be made, it is not a matter of doubt that it should be employed to assure the public good. It is easier to preserve health than to cure disease, and it implies less expense of means."