the tins are exhausted of air, for Vibriones and Bacteria live, as Pasteur has shown, without air or free oxygen. It is not because the boiled meats or vegetables are not putrescible or fermentable, as those who have had the misfortune to be in a ship supplied with unskilfully closed tins well know. What is it, therefore, but the exclusion of germs ? I think the Abiogenists are bound to answer this question before they ask us to consider new experiments of precisely the same order." ^
But admitting that life is always derived from life, the question still remains. Whether one kind of life may not give rise to life of a different kind ? It was long supposed that parasites derived their life from the plant or animal in which they live. And what is more to the point, it is a matter of familiar experience " that mere pressure on the skin will give rise to a corn " which seems to have a life of its own ; and that tumours are often developed in the body which acquire, as in the case of cancer, the power of multiplication and reproduction. In the case of vaccination, also, a minute par- ticle of matter is introduced under the skin. The result is a vesicle distended with vaccine matter " in quantity a hundred or a thou- sand-fold that which was originally inserted." Whence did it come ? Professor Huxley tells us that it has been proved that " the active element in the vaccine lymph is non-diffusible, and consists of miiuite particles not exceeding aoooo of an inch in diameter, which are made visible in the lymph by the microscope. Similar experiments have proved that two of the most destructive of epizo- otic diseases, sheep-pox and glanders, are also dependent for their existence and their propagation upon extremely small living solid particles, to which the title of microzymes is applied." The ques- tion, he says, arises whether these particles are the result of JSbmogenesis, or of Xenoffenesis, i. e., Are they produced by pre- existing living particles of the same kind ? or. Are they a modifi- cation of the tissues of the bodies in which they are found ? The decision of this question has proved to be a matter of vast practical importance. Some years since diseases attacked the grape-vine and the silk-worm in France, which threatened to destroy two of the most productive branches of industry in that country. The direct loss to France from the silk-worm disease alone, in the course of seventeen years, is estimated at two hundred and fifty millions of dollars. It was discovered that these diseases of the vine and worm, which were both infectious and contagious, were due to liv- 'ng organisms, by which they were propagated and extended. It
- Huxley's Address, as reported iu the London Athenceum, September 17, 1870, p. 376.
8 PART n. Ch. I. — origin of man.
became a matter of the last importance to determine whetlier these living particles propagated themselves, or whether they were pro- duced by the morbid action of the plant or animal. M. Pasteur, the eminent naturalist, sent by the French government to investi- gate the matter, after laborious research decided that they were independent organisms propagating themselves and multiplying with astonishuig rapidity. " Guided by that theory, he has devised a method of extirpating the disease, which has proved to be com- pletely successful wherever it has been properly carried out."^ Professor Huxley closes his address by saying that he had mvited his audience to follow him " in an attempt to trace the path which has been followed by a scientific idea, in its slow progress from the position of a probable hypothesis to that of an established law of nature." Biogenesis, then, accordmg to Huxley, is an established law of nature.^
Professor Tyndall deals with this subject in his lecture delivered in September, 1870, on " The Scientific Uses of the Imagination." He says that the question concerning the origm of life is, Wliether it is due to a creative fiat, ' Let life be ! ' or to a process of evolu- tion. Was it potentially in matter from the beginning ? or, Was it inserted at a later period ? However the convictions here or there may be influenced, he says, " the process must be slow which commends the hypothesis of natural evolution to the public mind. For what are the core and essence of this hj^othesis ? Strip it naked, and you stand face to face with the notion that not alone the more ignoble forms of animalcular or animal life, not alone the nobler forms of the horse and lion, not alone the
1 London Athenmum, September 17, 1870, p. 378. In view of the facts stated in the text, Professor Huxley asks, " How can we over-estimate the vahie of that knowledge of the nature of epidemic and epizootic diseases, and, consequently, of the means of checking or eradi- cating them, the dawn of which has assuredlj' commenced? Looking back no further than ten years, it is possible to select three (1863, 1864, and 1869) in which the total number of deaths from scarlet fever alone amounted to ninety thousand. That is the return of
killed, the maimed and disabled being left out of sight The facts which 1 have
•placed before you must leave the least sanguine without a doubt that the nature and causes of this scourge will one day be as well understood as those of the P^brine (the silk-worm disease) are now; and that the long-suffered massacre of our innocents will come to an end."
2 In quoting Professor Huxley as an authority on both sides of the question of spontane- ous generation, no injustice is done that distinguished naturalist. He wishes to believe that doctrine. His principles lead to that conclusion. But, as a question of scientific fact, he is constrained to admit that all the evidence is against it. He, therefore, does not believe it, although he thinks it may be true. Hence Mr. Mivart says that Professors Huxley and Tyndall, while tliey dissent from Dr. Bastian's conclusions in favour of spontaneous genera- tion, nevertheless "agree with him in principle, though they limit the evolution of the OTganic world from the inorganic to a very remote period of the world's history." Genesis oj Species, p. 266, note-