ATMOSPHERE IN RELATION TO PUTREFACTION AND INFECTION. 
61 
infusion was infected with a single drop of the distilled water furnished by Messrs. 
Hopkin and Williams ; twelve hours also sufficed to cloud the infusion thus treated. 
Precisely the same experiments were made with herring with the same result. In 
the winter season several days’ exposure to warmed air are needed to produce this effect. 
On the 31st of December a strong turnip-infusion was prepared by digesting in distilled 
water at a temperature of 120° Fahr. It was divided between four large test-tubes, in 
one of which the infusion was left unboiled, in another boiled for five minutes, and in 
the two remaining ones boiled, and after cooling infected with one drop of beef-infusion 
containing Bacteria. In twenty-four hours the unboiled tube and the two infected 
ones were cloudy, the unboiled tube being the most turbid of the three. The infusion 
in the unboiled tube was peculiarly limpid after digestion; for turnip it was quite 
exceptional, and no amount of searching with the microscope could reveal in it at first 
the trace of a living Bacterium ; still germs were there which, suitably nourished, passed 
in a single day into Bacterial swarms without number. Five days failed to produce an 
effect approximately equal to this in the uninfected boiled tube, which was exposed to 
the common laboratory air. 
There cannot, I think, be a doubt that the germs in the air differ widely among them- 
selves as regards preparedness for development. Some are fresh, others old ; some are 
dry, others moist. Infected by such germs the same infusion would require different 
lengths of time to develop Bacterial life. And this remark, I doubt not, applies to 
the different degrees of rapidity with which epidemic disease affects different people. In 
some the hatching-period, if I may call it such, is long, in some short, the differences 
depending upon the different degrees of preparedness of the contagium *. 
§ 25. Diffusion of Germs in the Air. 
During the earlier observations recorded in this paper, and others not here men- 
tioned, about 100 exposed tubes or flasks had been distributed irregularly in the rooms 
where the inquiry is conducted. They expanded to nearly 1000 in the end : not one 
of them escaped infection. A few days always sufficed to cloud the exposed 
infusions, and fill them with Bacterial life. I placed tubes at various points in the 
Royal Institution — on the roof of the house outside, in my bed-room, in an upper 
kitchen, in my study, in the upper and lower libraries, in the theatre, model-room, 
reading-room, manager’s room, and in a kitchen at the bottom of the house below the 
level of Albemarle Street. All were smitten with putrefaction, and with its invariable 
associate, Bacteria. In the rooms without fires the action was slower than in the warmer 
rooms ; but all the infusions gave way in the end. 
Considering the assertions which had been made regarding the scantiness of Bacteria- 
* The medical student of the future -will probably connect these remarks with the following statement of 
Dr. Muechison : — “ In that protean disease typhoid fever, I have repeatedly had occasion to observe a remark- 
able similarity in the course, and even in the complications, according to the source of the poison.” — Trans. 
Path. Soc. vol. xxvi. p. 315. 
