Jan. 27, 1876] 



NA TURE 



253 



We have here the oxygen, nitrogen, carbonic acid, 

 ammonia, aqueous vapour, and all the other gaseous 

 matters which mingle more or less with the air of a great 

 city. We have them, moreover, " untortured " by cal- 

 cination and unchanged even by filtration or manipula- 

 tion of any kind. The question now before us is, can air 

 thus retaining all its gaseous mixtures, but self-cleansed 

 from mechanically suspended matter, produce putrefac- 

 tion ? To this question both the animal and vegetable 

 worlds return a decided negative. 



Among vegetables experiments have been made with 

 hay, turnips, tea, coffee, hops, repeated in various ways 

 with both acid and alkaline infusions. Among animal 

 substances are to be mentioned many experiments with 

 urine ; while beef, mutton, hare, rabbit, kidney, liver, fowl, 

 pheasant, grouse, haddock, sole, salmon, cod, turbot, 

 mullet, herring, whiting, eel, oyster have been all subjected 

 to experiment. 



The result is that infusions of these substances exposed 

 to the common air of the Royal Institution laboratory, 

 maintained at a temperature of from 60' to 70° Fahr., all 

 fell into putrefaction in the course of from two to four 

 days. No matter where the infusions were placed, they 

 were infallibly smitten. The number of the tubes con- 

 taining the infusions was multiplied till it reached six 

 hundred, but not one of them escaped infection. 



In no single instance, on the other hand, did the air, 

 which had been proved moteless by the searching beam, 

 show itself to possess the least power of producing Bac- 

 terial life or the associated phenomena of putrefaction. 

 The power of developing such life in atmospheric air, and 

 the power of scattering light, are thus proved to be in- 

 dissolubly united. 



The sole condition necessary to cause these long-dor- 

 mant infusions to swarm with active life is the access of 

 the floating matter of the air. After having remained for 

 four months as pellucid as distilled water, the opening of 

 the back-door of the protecting case, and the consequent 

 admission of the mcte-laden air, suffice in three days to 

 render the infusions putrid and full of life. 



That such life arises from mechanically suspended par- 

 ticles is thus reduced to ocular demonstration. Let us 

 inquire a little more closely into the character of the par- 

 ticles which produce the Ufe. Pour Eau de Cologne into 

 water, a white precipitate renders the liquid milky. Or, I 

 imitating Briicke, dissolve clean gum mastic in alcohol, 

 and drop it into water, the mastic is precipitated, and | 

 milkiness produced. If the solution be very strong the | 

 mastic separates in curds ; but by gradually diluting the ; 

 alcoholic solution we finally reach a point where the 

 milkiness disappears, the liquid assuming, by reflected 

 light, a bright cerulean hue. It is, in point of fact, the I 

 colour of the sky, and is due to a similar cause, namely, i 

 the scattering of light by particles, small in comparison i 

 to the size of the waves of light. I 



When this liquid is examined by the highest micro- ' 

 scopic power it seems as uniform as distilled water. The 

 mastic particles, though innumerable, entirely elude the 

 microscope. At right angles to a luminous beam passing 

 among the particles they discharge perfectly polarised 

 light. The optical deportment of the floating matter of 

 the air proves it to be composed, in part, of particles of 

 this excessively minute character. When the track of 

 a parallel beam in dusty air is looked at horizontally 

 through a Nicol's prism, in a direction perpendicular to 

 the beam, the longer diagonal of the prism being vertical, 

 a considerable portion of the light from the finer matter is 

 extinguished. The coarser motes, on the other hand, 

 flash out with greater force, because of the increased 

 darkness of the space around them. It is among the 

 finest ultra-microscopic particles that the author shows the 

 matter potential as regards the development of Bacterial 

 Ufe is to be sought. 

 But though they are beyond the reach of the micro- 



scope, the existence of these particles, foreign to the 

 atmosphere but floating in it, is as certain as if they could 

 be felt between the fingers, or seen by the naked eye. 

 Supposing them to augment in magnitude until they 

 come, not only within range of the microscope, but within 

 range of the unaided senses. Let it be assumed that our 

 knowledge of them under these circumstances remains as 

 defective as it is now — that we do not know whether they 

 are germs, particles of dead organic dust, or particles of 

 mineral matter. Suppose a vessel (say a flower-pot) to 

 be at hand filled with nutritious earth, with which we mix 

 our unknown particles ; and that in forty-eight hours sub- 

 sequently buds and blades of well-defined cresses and 

 grasses appear above the soil. Suppose the experiment 

 when repeated over and overagain to yieldthe sameunvary- 

 ing result. What would be our conclusion ? Should we 

 regard those living plants as the products of dead dust 

 or mineral particles ; or should we regard them as the 

 offspring of living seeds ? The reply is unavoidable. We 

 should undoubtedly consider the experiment with the 

 flower-pot as clearing up our pre-existing ignorance ; we 

 should regard the fact of their producing cresses and 

 grasses as proof positive that the particles sown in the 

 earth of the pot were the seeds of the plants which have 

 grown from them. It would be simply monstrous to con- 

 clude that they had been " spontaneously generated." 



This reasoning applies word for word to the develop- 

 ment of Bacteria from that floating matter which the 

 electric beam reveals in the air, and in the absence of 

 which no Bacterial life has been generated. There seems 

 no flaw in this reasoning ; and it is so simple as to render 

 it unlikely that the notion of Bacterial life developed from 

 dead dust can ever gain currency among the members of 

 a great scientific profession. 



A novel mode of experiment has been here pursued, 

 and it may be urged that the conditions laid down by 

 other investigators in this field, which have led to different 

 results, have not been strictly attended to. To secure 

 accuracy in relation to these alleged results, the latest 

 words of a writer on this question, who has influenced 

 medical thought both in this country and in America, are 

 quoted. "We know," he says, "that boiled turnip or 

 hay-infusions exposed to ordinary air, exposed to filtered 

 air, to calcined air, or shut off altogether from contact 

 with air, are more or less prone to swarm with Bacteria 

 and vibriones in the course of from two to six days." 

 Who the " we " are who possess this knowledge is not 

 stated. The author is certainly not among the number, 

 though he has sought anxiously for knowledge of the kind. 

 He thus tests the statements in succesaion. 



And first, with regard to the filtered air. A group of twelve 

 large test-tubes were caused to pass air-tight through a slab 

 of wood. The wood was coated with cement, in which, while 

 hot, a heated "propagating glass" resembling a large 

 bell-jar was imbedded. The air within the jar was pumped 

 out several times, air filtered through a plug of cotton- 

 wool being permitted to supply its place. The test-tubes 

 contained infusions of hay, turnip, beef, and mutton — 

 three of each — twelve in all. They are as clear and 

 cloudless at the present moment as they were upon the 

 day of their introduction ; while twelve similar tubes, 

 prepared at the same time in precisely the same way and 

 exposed to the ordinary air, are clogged with mycelium, 

 mould, and Bacteria. 



With regard to the calcined air, a similar propagating 

 glass was caused to cover twelve other tubes filled with 

 the same infusions. The " glass " was exhausted and 

 carefully fiUed with air which had passed through a red- 

 hot platinum tube, containing a roll of red-hot platinum 

 gauze. Tested by the searching beam, the calcined air 

 was found quite free from floating matter. Not a speck 

 has invaded the limpidity of the infusions exposed to it, 

 while twelve similar tubes placed outside have fallen into 

 rottenness. 



