PUTEEFACTION AND INFECTION. 107 



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 themselves as regards 'pre- 

 jparedness 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 develope 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 

 essay, and others not here mentioned, about 100 ex- 

 posed tubes or flasks had been distributed irregularly in 

 the rooms where the inquiry is conducted. They ex- 

 panded 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 Eoyal Institu- 

 tion —on the roof of the house outside, in my bedroom, 

 in an upper kitchen, in my study, in the upper and 

 lower libraries, in the theatre, model-room, reading-room, 

 managers' room, and in the kitchen at the bottom of 

 the house below the level of Albemarle Street. All 

 were smitten, with putrefaction, and with its invariable 



' The medical student of the future will probably connect these 

 remarks with the following statement of Dr. Murchison : — ' In 

 that protean disease typhoid fever, I have repeatedly had occasion 

 to observe a remarkable similarity in the com-se, and even in the 

 complications, according to the source of the poison.' — Trans. Path. 

 Soc. vol. xxvi. p. 315. 



