that "sometimes animals are formed in putrefying soil, sometimes in plants, and sometimes in the fluids of other animals." He also formulated a principle that "every dry substance which becomes moist, and every moist body which becomes dried, produces living creatures, provided it is fit to nourish them."

Three centuries later, in his disquisition upon the Pythagorean philosophy, we find Ovid defending the same doctrine:1

"By this sure experiment we know

That living creatures from corruption grow:
Hide in a hollow pit a slaughter'd steer,

Bees from his putrid bowels will appear,

Who, like their parents, haunt the fields and bring
Their honey-harvest home, and hope another spring
The warlike steed is multiplied, we find,

To wasps and hornets of the warrior kind.
Cut from a crab his crooked claws, and hide
The rest in earth, a scorpion thence will glide,
And shoot his sting; his tail in circles toss'd
Refers the limbs his backward father lost;

And worms that stretch on leaves their filmy loom
Crawl from their bags and butterflies become.
The slime begets the frog's loquacious race;
Short of their feet at first, in little space,

With arms and legs endued, long leaps they take,
Raised on their hinder part, and swim the lake,
And waves repel; for nature gives their kind,
To that intent, a length of legs behind."

Not only was the doctrine of spontaneous generation of life current among the ancients, but we find it persisting through the Middle Ages, and descending to our own generation to be an accidental but important factor in the development of a new branch of science. In 1542, in his treatise called De Subtilitate, we find Cardan asserting that water engenders fishes, and that many animals spring from fermentation. Van Helmont gives special instructions for the artificial production of mice,

1 Ovid's Metamorphoses, translated by Mr. Dryden, published by Sir Samuel Garth, London, 1794.

and Kircher in his Mundus Subterraneus (chapter "De Panspermia Rerum ") describes and actually figures certain animals which were produced under his own eyes by the transforming influence of water on fragments of stems from different plants.'

About 1668, Francesco Redi seems to have been the first to doubt that the maggots familiar in putrid meat arose de novo: "Watching meat in its passage from freshness to decay, prior to the appearance of maggots, he invariably observed flies buzzing around the meat and frequently alighting on it. The maggots, he thought, might be the half-developed progeny of these flies. Placing fresh meat in a jar covered with paper, he found that although the meat putrefied in the ordinary way, it never bred maggots, while meat in open jars soon swarmed with these organisms. For the paper he substituted fine wire gauze, through which the odor of the meat could rise. Over it the flies buzzed, and on it they laid their eggs, but the meshes being too small to permit the eggs to fall through, no maggots generated in the meat; they were, on the contrary, hatched on the gauze. By a series of such experiments Redi destroyed the belief in the spontaneous generation of maggots in meat, and with it many related beliefs."

It was not long before Leeuwenhoek, Vallismeri, Swammerdan, and others, following the trend of Redi's work, contributed additional facts in favor of his view, and it may safely be asserted that ever since the time of this eminent man the tide of scientific opinion has turned more and more strongly against the idea that life is spontaneously generated.

About this time (1675) one whose name has been already mentioned, Anthony van Leeuwenhoek, and who is justly called the "Father of microscopy," came into prominence. An optician by trade, Leeuwenhoek devoted much time to the perfection of the compound microscope, which was just coming into use. The science of 1 See Tyndall: Floating Matter in the Air.

optics, however, was not sufficiently developed to enable him to overcome the errors of refraction, and after the loss of much time he turned to the simple lens, using it in so careful and remarkable a manner as to be able to record his observations in one hundred and twelve contributions to the Philosophical Transactions. Leeuwenhoek, among other things, demonstrated the continuity of arteries and veins through intervening capillaries, thus affording ocular proof of Harvey's discovery of the circulation of the blood; discovered the rotifers, and also the bacteria, seeing them first in saliva.

Although one of those who contributed to the support of Redi's arguments against the spontaneous generation of maggots, Leeuwenhoek involuntarily reopened the old controversy about spontaneous generation by bringing forward a new world, peopled by creatures of such extreme minuteness as to suggest not only a close relationship to the ultimate molecules of matter, but an easy transition from them.

In succeeding years the development of the compound microscope showed these minute organisms to exist in such numbers that putrescent infusions, both animal and vegetable, literally teemed with them, one drop of such a liquid furnishing a banquet for millions.

Much hostility arose in the scientific world as years went on until two schools attained prominence—one headed by Buffon, whose doctrine was that of "organic molecules;" the other championed by Needham, whose doctrine was the existence of a "vegetative force" which drew the molecules together.

Experimentation was begun and attracted much attention. Among the pioneers was Abbé Lazzaro Spallanzani (1777), who filled flasks with organic infusions, sealed their necks, and, after subjecting their contents to the temperature of boiling water, placed them under conditions favorable for the development of life, without, however, being able to produce it. Spallanzani's critics, however, objected to his experiment on the ground that

air is essential to life, and that in his flasks the air was excluded by the hermetically-sealed necks.

Schulze (1836) set the objection aside by filling a flask only half full of distilled water, to which animal and vegetable matters were added, boiling the contents to destroy the vitality of any organisms which might already exist in them, then sucking daily into the flask a certain amount of air which had passed through a series of bulbs containing concentrated sulphuric acid, in which it was supposed that whatever germs of life the air might contain would be destroyed. This flask was kept from May to August; air was passed through it daily, yet without the development of any infusorial life.

The term "infusorial life" having been used, here it is well to observe that during all the early part of their recognized existence the bacteria were regarded as animal organisms and classed among the infusoria.

Cagniard Latour and Schwann in the year 1837 succeeded in proving that the minute oval bodies which had been observed in yeast since the the time of Leeuwenhoek were living organisms-vegetable forms-capable of growth; and when Boehm succeeded a year later in demonstrating their occurrence in the stools of cholera, and conjectured that the process of fermentation was concerned in the causation of that disease, the study of these low forms of life received an immense impetus from the important position which they began to assume in relation to medical science.

The experiments of Schwann, by proving that the free admission of calcined air to closed vessels containing putrescible infusions was without effect, while the admission of ordinary air brought about decomposition, suggested that the causes of putrefaction which were in the air were living entities.

In 1862, Pasteur published a paper "On the Organized Corpuscles existing in the Atmosphere," in which he showed that many of the floating particles which he had been able to collect from the atmosphere of his

laboratory were organized bodies. If these were planted in sterile infusions, abundant crops of micro-organisms were obtainable. By the use of more refined methods he repeated the experiments of Schwann and others, and showed clearly that "the cause which communicated life to his infusions came from the air, but was not evenly distributed through it."

Three years later he showed that the organized corpuscles which he had found in the air were the spores or seeds of minute plants, and that many of them possessed the property of withstanding the temperature of boiling water a property which explained the peculiar results. of many previous experimenters, who failed to prevent the development of life in boiled liquids enclosed in hermetically-sealed flasks.

Chevreul and Pasteur (about 1836) proved that animal solids did not putrefy or decompose if kept free from the access of germs, and thus suggested to surgeons that the putrefaction which occurred in wounds was due rather to the entrance of something from without than to some change within. The deadly nature of the discharges from these wounds had been shown in a rough manner by Gaspard as early as 1822 by injecting some of the material into the veins of animals.

Examinations of the blood of diseased animals were now begun, and Pollender (1849) and Davaine (1850) succeeded in demonstrating the presence of the anthrax bacillus in that disease. Several years later (1863) Davaine, having made numerous inoculation-experiments, demonstrated that this bacillus was the materies morbi of the disease.

Tyndall enlarged upon the experiments of Pasteur, and very conclusively proved that the micro-organismal germs were in the dust suspended in the atmosphere, not ubiquitous in their distribution. His experiments were very ingenious and are of interest to medical men. First preparing light wooden chambers, with one large glass window in the front and one smaller window in each.