Now, the common preventives against infection are such as are peculiarly inimical to every kind of insect; camphor, chloride of lime, tobacco-smoke, and powerful scents and smokes of any kind. The first impulse on the appearance of an infectious disease is to purify everything as much as possible, and by extra cleanliness and fumigations to endeavor to arrest its progress. The great purifier of Nature is a violent wind, which usually terminates an epidemic immediately; this would naturally carry before it all insect life with which the atmosphere might be impregnated, and the disease disappears at the same moment. It will he well remembered that the plague of locusts inflicted upon Pharaoh was relieved in the same manner: "And the Lord turned a mighty strong west wind, which took away the locusts and cast them into the Red Sea; there remained not one locust in all the coasts of Egypt."

Every person is aware that unwholesome air is quite poisonous to the human system as impure water; and seeing that the noxious qualities of the latter are caused by animalcules, and that the method used for purifying infected air are those most generally destructive to insect life, it is not irrational to conclude that the poisonous qualities of bad water and bad air arise from the same cause.

Man is being constantly preyed upon by insects; and were it not for ordinary cleanliness, he would become a mass of vermin; even this does not protect him from the rapacity of ticks, mosquitoes, fleas and many others. Intestinal worms feed on him within, and, unseen, use their slow efforts for his destruction.

The knowledge of so many classes which actually prey upon the human system naturally leads to the belief that many others endowed with the same propensities exist, of which we have at present no conception. Thus, different infectious disorders might proceed from peculiar species of animalcules, which, at given periods, are wafted into certain countries, carrying pestilence and death in their invisible course.

A curious phenomenon has recently occurred at Mauritus, where that terrible scourge, the cholera, has been raging with desolating effect.

There is a bird in that island called the "martin," but it is more property the "mina." This bird is about the size of the starling, whose habits its possesses in a great degree. It exists in immense numbers, and is a grand destroyer of all insects. On this account it is seldom or never shot at, especially as it is a great comforter to all cattle, whose hides it entirely cleans from ticks and other vermin, remaining for many hours perched upon the back of one animal, while its bill is actively employed in searching out and destroying every insect.

During the prevalence of the cholera at Mauritius these birds disappeared. Such a circumstance had never before occurred, and the real cause of their departure is still a mystery.

May it not have been, that some species of insect upon which they fed had likewise migrated, and that certain noxious animalcules, which had been kept down by this class, had thus multiplied within the atmosphere until their numbers caused disease? All suppositions on such a subject must, however, remain in obscurity, as no proof can be adduced of their correctness. The time may arrive when science may successfully grapple with all human ailments, but hitherto that king of pestilence, the "cholera," has reduced the highest medical skill to miserable uncertainty.

(Editor：control)