454 



Dr. W. Roberts on the Influence of 



[Dec. 21, 



III. Note on the Influence of Liquor Potassae and an Elevated 

 Temperature on the Origin and Growth of Microphytes.^-' 

 By Wm. Roberts, M.D. Communicated by Prof. Tyndall, 

 F.R.S. Received December 18, 1876. 



In a recent communication to the Royal Society, Dr. Rastian * brought 

 forv^'ard some experiments to show that while an acid urine usually 

 remains barren after being boiled a few minutes, the same urine becomes 

 fertile when similarly treated if previously neutralized or rendered 

 alkaline by liquor potassse, especially if it be afterwards maintained at a 

 temperatiu^e of 115° F. or 122° P* In this respect urine only conforms 

 to the general rule observed by myself and formulated in my previous 

 communication to the Society t — that " shghtly alkaline liquids were 

 always more dijfficult to sterihze (by heat) than shghtly acid hquids." 



This difference came out strongest in my own experiments in the case 

 of hay-infusion — the acid infusion invariably remaining barren after a 

 few minutes boiling, and the neutrahzed infusion invariably becoming 

 fertile after a similar boiling. Accordingly I utilized hay-infusion to 

 determine the cause of the difference in question. It could evidently 

 only be due to one of two things — either (1) the change of reaction 

 enabled germs preexisting in the mf usion to survive the ebullition, or 

 (2) the addition of the alkali exercised a positive influence in exciting a 

 de novo generation of organisms. To decide which of these two inter- 

 pretations was the true one, an experiment was contrived in v hich the 

 Hq. potassae could be added to the infusion not before, but after it had 

 been boiled, and thereby rendered permanently sterile. "WHien added in 

 this way, I found that liquor potassae had not any power to excite germina- 

 tion. The infusions invariably remained barren when the alkali was 

 added to them after they had been sterilized. I therefore concluded 

 that the effect of the change of reaction consisted simply in enabling 

 preexistmg germs to survive a brief ebullition. Dr. Bastian, in repeat- 

 ing this experiment in the case of urine, arrived at an opposite con- 

 clusion : he found that whether the alkali was added before or after 

 ebullition he obtained the same result — the urine in both cases became 

 fertile ; and he concluded that the alkali had a positive power of pro- 

 moting the origin of organisms in the urine. 



This experiment, if properly performed, is obviously a crucial one, 

 and it is recognized as such by Dr. Bastian. But two conditions are 

 essential to the vahdity of the experiment. In the first place, it must 

 be ascertained beyond doubt that the boiled acid fluid has been really 

 deprived of its germs — in other words, that the ebullition has been 

 sufficiently prolonged to render it permanently barren; and secondly, 



* " Eesearches illustrative of the Phvsico-Ohemical Theory of Fermentation," &c. 

 See ante, p. 149. 



t " Studies on Biogenesis," Phil. Trans, vol. clxiv. p. 457. 



