PUTREFACTION AND FERMENTATION 487 



elapsed, a considerable fraction of a cubic inch of fresh air has entered every 

 night into the body of each flask to exert its influence upon the liquid. In the 

 case of the flasks with contorted neck, the air moving to and fro through the 

 tube soon dried the moisture which was at first deposited within it ; and any of 

 you may see, after lecture, that in the one before you the neck is dry as well 

 as open from end to end, so that it could present no obstacle to any gaseous 

 constituent of the atmosphere. Nevertheless, though thus freely exposed to the 

 action of the gases of the air for so long a period, including two unusually hot 

 summers, the urine still retains its original straw colour and perfect transparency, 

 presenting neither cloud, scum, nor sediment ; and the only change that I can 

 detect in it is, that of late, as a result, I presume, of the slow evaporation that 

 has been going on in consequence of the perpetual change of air, some very 

 minute shining crystals have been deposited upon the sides of the glass. Simi- 

 larly unaltered are the contents of the other two similar flasks which I have not 

 thought it needful to bring here. But very different is the appearance of the 

 urine in this other flask, whose neck, short and vertical, was calculated to admit 

 particles of dust as well as gaseous material. The transparent straw colour has 

 given place to a muddy brown, with abundant sediment, including the debris of 

 different fungi, which have long since ceased to grow, poisoned, no doubt, by the 

 acridity of the liquid, the pungently ammoniacal character of which may be 

 readily ascertained by placing the warm hand for a moment upon the body of 

 the flask, while one nostril is kept above the orifice. 



Soon after the commencement of the experiment, this short-necked flask had 

 a really beautiful appearance. Two different kinds of fungi presented them- 

 selves — one of exceedingly delicate structure growing rapidly from the bottom 

 of the vessel, so as to occupy in no long time the greater part of the bulk of the 

 liquid ; the other a dense blue mould floating at the surface, and extending 

 slowly in concentric rings. Meanwhile the fluid gradualh' assumed a deeper 

 and deeper amber tint, indicative of progressive change in its chemical com- 

 position. 



In the case of the flasks with bent necks I was not content with observing 

 the completely unchanged appearance of the contained urine. Half a year after 

 the experiment was begun I poured out about half an ounce of the clear contents 

 of one of them into a wine-glass for examination. Its odour was perfectly sweet, 

 and its reaction faintly acid ; and under the microscope a careful search with an 

 excellent glass of high power failed to detect vibrio, bacterium, or any other 

 organism. The lowest known forms of organic development and the slightest 

 approach to putrefactive change had been ahke prevented by simph' filtering, 

 the air of its floating molecules. 



