Fortunately, and it is again to Mr. Pasteur that we owe these wonderful discoveries, the parasitic microbes themselves, which sow sickness and death, may, through proper culture, become true vaccine viri that are capable of preserving the organism against any future attack of the disease that they were capable of producing; such vaccine matters have been discovered for charbon, chicken cholera, the measles of swine, etc.
When the micrococcus of chicken cholera (Fig. 3.) is cultivated, it is seen that the activity of the microbe in cultures exposed to the air gradually diminishes. While a drop of the liquid would, in twenty-four hours, have killed all the chickens that were inoculated with it, its effect after two, three, or four days considerably diminishes, and an inoculation with it produces nothing more than a slight indisposition in the animal, and one that is never followed by a serious accident. It is then said that the virulence of the microbe is attenuated.
The air is the agent of this transformation that gradually renders the bacteria benign, for in cultures made under the same circumstances as the preceding, but with the absence of air, the activity of these algæ is preserved for days or weeks, and they will then cause death just as surely as they would have done at the end of one day.
What is remarkable is that animals inoculated with the attenuated micrococcus become for a varying length of time refractory to the action of the most formidable parasites of this kind. Mr. Pasteur has discovered two such vaccine viri--one for chicken cholera and the other for charbon. His results have not been accepted without a struggle, and it required nothing less than public experiment in vaccination, both in France and abroad, to convince the incredulous. There are still people at the present time who assert that Mr. Pasteur's process of vaccination has not a great practical range! And yet, here we have the results; more than 400,000 animals have been vaccinated since 1881, and it has been found that the mortality is ten times less in these than in those that have not been vaccinated!
An impetus has now been given, and we can look to the future with confidence, for, if our enemies are numerous, the use of a severe hygiene and preventive vaccination will permit us to gradually free humanity from the terrible scourges that sap the sources of fortune and life.--Science et Nature.
THE WINE FLY.
At the last meeting of the New York Microscopical Society, a paper was read by Dr. Samuel Lockwood, secretary of the New Jersey State Microscopical Society. His subject was the Wine Fly, Drosophila ampelophila. The paper was a contribution to the life-history of this minute insect. He had given in part three years to its study, beginning in September, 1881, when nothing whatever of its life-history seemed to have been known. In October the flies attacked his Concords. He found upon a grape which he was inspecting with a pocket-lens an extremely small white egg; but lost it. The grapes when brought on the table were infested by the flies, which proved to be the above mentioned species. When driven from the grapes they would fly to the window, where he captured two of them These were placed in a jar with a grape for food. In two days he found one egg on the outer skin of the grape. The laying was kept up for four or five days, until there were about thirty, some on the outside of the grape and some at an opening where the two flies had fed. The egg had a pair of curious suspenders near the end where the mouth of the larva would develop. These suspenders were attached at their ends to the grape, but where the egg was laid in the soft part of the fruit the suspenders were spread out at the surface; thus the larva would emerge clean from the shell. The egg was 0.5 mm. in length, and about a fourth of that in width. The larva when grown was at least four times as long as the egg. As the larva burrowed in the juices of the fruit, two quite prominent breathing tubes at the posterior end were kept in the air. Between these cardinal tubes were several teat-like points, much smaller, but having a similar function.
The larvae appeared in five days after the eggs were laid. In about as many more days the puparium state would be entered, and in about six days more the fly or imago would appear. In ovipositing the suspensors would leave the oviparous duct last. The paper claimed that the curious shape of the egg compelled the female to oviposit slowly, as it took time for the egg to assume its form; hence, the eggs were not laid in strings or masses, but singly and at considerable intervals.