Biology and Its Makers / With Portraits and Other Illustrations

by William A. Locy

Fig. 91.—Apparatus of Tyndall for Experimenting on Spontaneous Generation.

Tyndall.—John Tyndall (1820-1893), the distinguished physicist, of London, published, in 1876, the results of his experiments on this question, which, for clearness and ingenuity, have never been surpassed. For some time he had been experimenting in the domain of physics with what he called optically pure air. It was necessary for him to have air from which the floating particles had been sifted, and it occurred to him that he might expose nutrient fluids to this optically pure air, and thus very nicely test the question of the spontaneous origin of life within them.

He devised a box, or chamber, as shown in Fig. 91, having in front a large glass window, two small glass windows on the ends, and in the back a little air-tight trap-door. Through the bottom of this box he had fitted ordinary test tubes of the chemist, with an air-tight surrounding, and on the top he had inserted some coiled glass tubes, which were open at both ends and allowed the passage of air in and out of the box through the tortuous passage. In the middle of the top of the box was a round piece of rubber. When he perforated this with a pinhole the elasticity of the rubber would close the hole again, but it would also admit of the passage through it of a small glass tube, such as is called by chemists a "thistle tube." The interior of this box was painted with a sticky substance like glycerin, in order to retain the floating particles of the air when they had once settled upon its sides and bottom. The apparatus having been prepared in this way, was allowed to stand, and the floating particles settled by their own weight upon the bottom and sides of the box, so that day by day the number of floating particles became reduced, and finally all of them came to rest.

The air now differed from the outside air in having been purified of all of its floating particles. In order to test the complete disappearance of all particles. Tyndall threw a beam of light into the air chamber. He kept his eye in the darkness for some time in order to increase its sensitiveness; then, looking from the front through the glass into the box, he was able to see any particles that might be floating there. The floating particles would be brightly illuminated by the condensed light that he directed into the chamber, and would become visible. When there was complete darkness within the chamber, the course of the beam of light was apparent in the room as it came up to the box and as it left the box, being seen on account of the reflection from the floating particles in the air, but it could not be seen at all within the box. When this condition was reached, Tyndall had what he called optically pure air, and he was now ready to introduce the nutrient fluids into his test tubes. Through a thistle tube, thrust into the rubber diaphragm above, he was able to bring the mouth of the tube successively over the different test tubes, and, by pouring different kinds of fluids from above, he was able to introduce these into different test tubes. These fluids consisted of mutton broth, of turnip-broth, and other decoctions of animal and vegetable matter. It is to be noted that the test tubes were not corked and consequently that the fluids contained within them were freely exposed to the optically pure air within the chamber.

The box was now lifted, and the ends of the tubes extending below it were thrust into a bath of boiling oil. This set the fluids into a state of boiling, the purpose being to kill any germs of life that might be accidentally introduced into them in the course of their conveyance to the test tubes. These fluids, exposed freely to the optically pure air within this chamber, then remained indefinitely free from micro-organisms, thus demonstrating that putrescible fluids may be freely exposed to air from which the floating particles have been removed, and not show a trace either of spoiling or of organic life within them.

It might be objected that the continued boiling of the fluids had produced chemical changes inimical to life, or in some way destroyed their life-supporting properties; but after they had remained for months in a perfectly clear state, Tyndall opened the little door in the back of the box and closed it at once, thereby admitting some of the floating particles from the outside air. Within a few days' time the fluids which previously had remained uncontaminated were spoiling and teeming with living organisms.

These experiments showed that under the conditions of the experiments no spontaneous origin of life takes place. But while we must regard the hypothesis of spontaneous generation as thus having been disproved on an experimental basis, it is still adhered to from the theoretical standpoint by many naturalists; and there are also many who think that life arises spontaneously at the present time in ultra-microscopic particles. Weismann's hypothetical "biophors," too minute for microscopic observation, are supposed to arise by spontaneous generation. This phase of the question, however, not being amenable to scientific tests, is theoretical, and therefore, so far as the evidence goes, we may safely say that the spontaneous origin of life under present conditions is unknown.

Practical Applications.—There are, of course, numerous practical applications of the discovery that the spoiling of putrescible fluids is due to floating germs that have been introduced from the air. One illustration is the canning of meats and fruits, where the object is, by heating, to destroy all living germs that are distributed through the substance, and then, by canning, to keep them out. When this is entirely successful, the preserved vegetables and meats go uncontaminated. One of the most important and practical applications came in the recognition (1867) by the English surgeon Lister that wounds during surgical operations are poisoned by floating particles in the air or by germs clinging to instruments or the skin of the operator, and that to render all appliances sterile and, by antiseptic dressings, completely to prevent the entrance of these bacteria into surgical wounds, insures their being clean and healthy. This led to antiseptic surgery, with which the name of Lister is indissolubly connected.