698 THE POPULAR SCIENCE MONTHLY. 



whiting. To the present hour, the beef and mutton tubes remain as 

 limpid as distilled water. Just as in the case of living men and women 

 in Edinburgh, no amount of fetid gas had the power of profagating 

 the plague so long as the organisms which constitute the true con- 

 tagium did not gain access to the infusions. 



The universal prevalence of the germinal matter of bacteria in 

 water has been demonstrated with the utmost evidence by the experi- 

 ments of Dr. Burdon Sanderson. But the germs in water are in a very- 

 different condition, as regards readiness for development, from those 

 in air. In water they are thoroughly wetted, and ready, under the 

 l)ro2Der conditions, to pass rapidly into the finished organism. In air 

 they are more or less desiccated, and require a period of preparation 

 more or less long to bring them up to the stai'ting-point of the water- 

 germs. The rapidity of development, in an infusion infected by either 

 a speck of liquid containing bacteria or a drop of water, is extraor- 

 dinary. On January 4th, a thread of glass almost as fine as a bair was 

 dipped into a cloudy turnip-infusion, and the tip only of the glass fibre 

 was introduced into a large test-tube containing an infusion of red 

 mullet ; twelve hours subsequently, the perfectly pellucid liquid was 

 cloudy throughout and full of life. A second test-tube containing the 

 same 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 

 Avere made with herring with the same result. At this season of the 

 year several days' exposure to the air are needed to produce the same 

 effect. On December 31st, a strong turnip-infusion was prepared by 

 digesting in distilled water at a temperature of 120 Fahr. The infu- 

 sion was divided between four large test-tubes, in one of which it was 

 left unboiled, in another boiled for five minutes, and in the two remain- 

 ing ones boiled, and, after cooling, infected with one drop of beef- 

 infusion containing bacteria. In twenty-four hoiirs, the unboiled tube 

 and the two infected ones were cloudy ; the unboiled tube being the 

 most turbid of the three. The infusion here was peculiai'ly 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 have not sufficed to produce an effect approximately equal to this 

 in the boiled tube, which was uninfected but exposed to the common 

 laboratory air. 



There cannot, moreover, be a doubt that the germs in the air differ 

 widely among themselves 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. This remark applies to and explains the 

 different degrees of rapidity with which epidemic disease acts upon 



