1885.] on the Mechanical Production of Cold, &c. 311 



ing substances are sealed up in a comparatively small space contain- 

 ing air, the processes are arrested when all the oxygen has been used 

 up, and the products of putrefaction may undergo no further altera- 

 tion. In these circumstances, in such experiments as ours, the 

 apparent arrest of putrefaction in sealed vessels might have been 

 attributed to the action on the organisms of the low temperature to 

 which they had been exposed, instead of to the real cause — the 

 removal of all the oxygen from the confined air. To meet this 

 difficulty the importance was seen of testing the effect of cold on 

 putrescible substances placed in test tubes and flasks firmly plugged 

 with cotton-wool, through which there might be a free play between 

 the gases in the tube or flask and the surrounding atmosphere. Nor 

 was it necessary in such experiments to sterilise the cotton- wool by' 

 heat, as must be done in all researches on the effects of high 

 temperatures, because if a low temperature were fatal to micro- 

 organisms, it would kill those in the cotton-wool as well as those 

 in the putrescible substances. Many experiments were made with 

 tubes and flasks stopped with cotton-wool plugs instead of being 

 hermetically sealed, but there was no difference in the general 

 result. 



6. Six flasks were filled with fresh urine, and plugged with 

 cotton- wool, on the 10th of December. The first one plugged with 

 wool was exposed to the temperature of the engineering shop where 

 the experiments were carried on (about 50^ F.), and on the 13th the 

 urine was muddy ; on the 18th it was found to be swarming with 

 bacteria and vibrios. The second was exposed for eight hours to 

 zero F. ; on the 13th it showed slight muddiness, and on the 18th it 

 was swarming with bacteria. The third was exposed to a tempera- 

 ture of — 10^ F. for eight hours, and on the 18th it was also 

 swarming with bacteria. The fourth was exposed to — 20° F. with 

 the same result. The fifth was exposed to — 30° F. with a like 

 result. The sixth was exposed to — 80° F., and it did not become 

 muddy until the 22nd, that is, twelve days after the beginning of 

 the experiment. These results showed that freezing at very low 

 temperatures delayed the appearance of the alkaline fermentation 

 due to organisms, but a temperature of — 80° for eight hours did 

 not sterilise the urine. 



7. Samples of fresh milk, exposed to temperatures of from zero to 

 — 80° F. for eight hours, curdled, and showed the well-known 

 bacterium lactis, and, so far as could be observed, freezing did not 

 delay the process after the flasks were kept at a temperature of about 

 50° F. 



8. Samples of Prestonpans beer (containing about 2 per cent, of 

 alcohol) were similarly treated. Exposed to the air of the shop, a 

 scum of torulae made its appearance in three days- Freezing un- 

 doubtedly delayed the appearance of these in flasks plugged with 

 cotton-wool, and the delay corresponded to the fall of temperature, 

 so that the sample exposed to — 80° F. did not show the scum for 



