Professw Tyndall on Germs. 307 



then showed the air within it to be laden with floating matter. 

 On the 13th it was again examined. Before the beam entered, 

 and after it quitted the case, its track was vivid in the air, but 

 within the case it vanished. Three days of quiet sufficed to cause 

 all the floating matter to be deposited on the sides and bottom, 

 where it was retained by a coating of glycerine, with which the 

 interior surface of the case had been purposely varnished. The 

 test-tubes were then filled through the pipette, boiled for five 

 minutes in a bath of brine or oil, and abandoned to the action of 

 the raoteless air. During ebullition aqueous vapor rose from the 

 liquid into the chamber, where it was for the most part condensed, 

 the uncondensed portion escaping, at a low temperature through 

 the bent tubes at the top. Before the brine was removed little 

 stoppers of cotton-wool were inserted in the bent tubes, lest the 

 entrance of the air into the cooling chamber should at first be for- 

 cible enough to carry motes along with it. As soon, however, as 

 the ambient temperature was assumed by the air within the case, 

 the cotton-wool stoppers were removed. 



We have here the oxygen, nitrogen, carbonic acid, ammonia, 

 aqueous vapor, and all the other gaseous matters which mingle 

 more or less with the air of a great city. We have them, more- 

 over, " untortured" by calcination and unchanged even by filtra- 

 tion or manipulation 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 putrefaction ? To 

 this question both the animal and vegetable worlds return a 

 decided negative. 



Among vegetables, experiments have been made with hay, tur- 

 nips, tea, coiFee, hops, repeated in various ways with both acid 

 and alkaline intusions. Among animal substances are to be men- 

 tioned many experiments with urine ; while beef, mutton, hare, 

 rabbit, kidney, liver, fowl, pheasant, grouse, haddock, solo, sal- 

 mon, cod, turbot, mullet, herring, whiting, eel, oyster have beiii 

 all subjected to experiment. fe' ' ^ 



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 infu- 

 sions were placed, they were infallibly smitten. The number of the 

 tubes containing the infusions was multiplied till it reached six 

 hundred, but not one of them escaped infection. 



On the other hand, in no single instance did the air, which had 

 been proved raoteless bv the searching beam, show itself to possess 

 the least power of producing Bacterial 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 uidissolubly united. 



. ^^® sole condition necessary to cause these long-dormant infu- 

 sions to swarm with active life is the access of the floating matter 

 of the air. After having remained for four months as pellucid as 



