theory, he would have contended that these ova, which originally looked alike, were, indeed, alike at first, but that all the differences manifested afterwards by different races of animals were simply modifications received from the particular animals through which they received their development. It is probable, however, that the Doctor looked farther, and saw what effect this theory of original individual differences would have in another direction.

Sure enough, why should there not be individual differences from the very beginning of life? But where is this beginning? Certainly it is before the ovum gets to be a one-hundredand-fiftieth of an inch in diameter, as it is generally, when examined with the microscope. Probably at this time it has thousands, and, perhaps, millions, of molecules in its organism; and the innate composition of the ova of the man, dog, horse, etc., may be as different as the hundreds of chemical combinations, which can be made from a few simple chemical constituents, some of which combinations, as water, may be perfectly harmless; while others, like sulphuric acid, gunpowder, or corrosive sublimate, may be peculiarly destructive. So the differences of the very natures which are contained in these eggs which look alike may be originally as great as we find them in adult men, dogs, and horses.

The original natures inhere in the ova, and we have no reason to suppose that the differences in their original natures are not as real in these ova as they are in the mature animals.

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CHAPTER IX.

THIS CHAPTER CONTAINS A SHORT HISTORY OF DISCUSSIONS CONCERNING THE SUBJECTS CONSIDERED IN THE LAST CHAPTER, AND EXTRACTS FROM THE RECORDS OF EXPERIMENTS MADE BY PROF. TYNDALL UPON GERMINATING FLUIDS.

THE writings of Aristotle generally controlled the science of natural history for two thousand years, and in fact Aristotle may be called "the Father of Natural History." Aristotle denied "the eternity of the individual," and contended that the individual came into existence "in the act of generation, and perished at death.”

But if Aristotle was right in this supposition, of which he gave no proof, that does not answer the question, "Whence is life?" For two thousand years succeeding Aristotle the doctrine of "spontaneous generation" was generally accepted by scientific men. Caterpillars and insects which infest trees and vegetables were supposed to be spontaneously generated. Because putrefying flesh was infested with worms, or other living creatures, the supposition was that these came spontaneously. No one was able to show that this was otherwise until A.D. 1668, when Dr. Francisco Redi, of Tuscany, while watching meat ready to decay noticed flies alight upon it, and suspected that the maggots which followed were in some way connected with these flies. He then placed meat in jars so covered that the flies could not get access to it, and found that, although it putrefied, no maggots came. He

then put gauze over the mouth of the jars, and he found that the flies hovered over the meat, and laid their eggs on the gauze, and they hatched out there, but no maggots came in the meat. Other physicians and philosophers continued these observations and experiments; and though improvements in the microscope helped to dispel the illusions of centuries respecting the generation of the larger insects, etc., yet the animalcules found in stagnant water were still believed to be spontaneously generated. For about two hundred years succeeding, many distinguished men were ranged on each side of the controversy, and not until within the past twenty years have anything like positive results been reached on this question.

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As late as 1872 Dr. H. C. Bastian published his views on abiogenesis, and strongly advocated the doctrine of 'spontaneous generation." Speculations concerning the origin of bacterial life become intimately connected with the germ theory of diseases.

Do diseases originate themselves? or are they propagated as vegetable and animal life are propagated? Do putrefactive germs breed from previous germs? Or do they originate spontaneously? Closely connected with the germ theory comes the "antiseptic system of surgery" of Prof. Lister, which has rendered surgical operations comparatively safe which, a few years ago, were exposed to extreme peril. Prof. Lister, like Pasteur, Dr. Budd, Prof. Tyndall, and others, believes that all putrefactive diseases originate from diseasegerms which float in the air and readily attach themselves to any person or substance which is susceptible to their action. Dr. W. B. Carpenter writes, in the "Nineteenth Century," of Prof. Lister's theory (as quoted in "Popular Science Monthly," Dec., 1881, p. 248): "Among the most

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immediately productive of its results may be accounted the 'antiseptic surgery' of Prof. Lister, of which the principle is the careful exclusion of living bacteria and other germs alike from the natural internal cavities of the body and from such as are formed by disease, whenever these may be laid open by accident or may have to be opened surgically. This exclusion is effected by the judicious use of carbolic acid, which kills the germs without doing any mischief to the patient; and the saving of lives, of limbs, and of severe suffering, already brought about by this method, constitutes in itself a glorious triumph alike to the scientific elaborator of the germ-doctrine and to the scientific surgeon by whom it has been thus applied."

M. Pasteur has cultivated various disease-germs as one would cultivate grain, and has discovered processes by which these germs may be rendered malignant, and in almost every case produce certain death to such as become inoculated with the deadly virus; and he has also discovered ways of rendering the same comparatively harmless. His experiments have been of immense advantage in stamping out deadly diseases among the flocks of France. He has also discovered the destroyers of the grape-vine of France. He proved them to be propagated by living germs, and provided a remedy against them.

The remarks of Dr. Carpenter are so directly in point and of such practical importance that I shall quote freely from his article. He says of the transmission of diseasegerms among flocks of sheep: "One of the first questions examined by Pasteur was the cause of outbreaks of 'charbon' in its most deadly form among flocks of sheep feeding in what appeared to be the healthiest pastures, far removed from any obvious source of infection. Learning by the in

quiries he instituted that special localities seemed haunted, at distant intervals, by this plague, he inquired what had been done with the bodies of the animals that had died of it, and learned that it had been customary to bury them deep in the soil, and that such interments had been made, it might have been ten years before, beneath the surface of some of the very pastures in which the fresh outbreaks took place. Notwithstanding that the depth (ten or twelve feet) at which the carcasses had been buried seemed to preclude the idea of the upward travelling of the poison-germs, the divining mind of Pasteur found in earthworms a probable means of their conveyance, and he soon obtained an experimental verification of his idea which satisfied even those who were at first disposed to ridicule it. Collecting a number of worms from these pastures, he made an extract of the contents of their alimentary canals, and found that the inoculation of rabbits and Guinea-pigs with this extract gave them the severest form of charbon,' due to the multiplication in their circulating current of the deadly anthrax-bacillus, with which their blood was found after death to be loaded.

"Another mode in which the disease-germs of anthrax may be conveyed to herds of cattle widely separated from each other and from any ostensible source of infection was discovered by the inquiries prosecuted, a few years ago, by Prof. Burdon-Sanderson at the Brown Institution, in consequence of a number of simultaneous outbreaks which occurred in different parts of the country. It was found that all the herds affected had been fed with brewers' grains, supplied from a common source; and, on examining microscopically a sample of these grains, they were seen to be swarming with the deadly bacillus, which, when it has once