302 



NATURE 



{Feb. I, 1877 



cules rebounding from it with a greater velocity than that 

 at which they struck it. The molecular pressure, there- 

 fore, in this case streams from the inner surface of the 

 warm spot of glass on which the heat rays have fallen, 

 and repels whatever happens to be in front of it, quite 

 irrespective of the colour of its surface. 



William Crookes 



THE SPONTANEOUS GENERATION 

 QUESTION 



'T*WO contributions have recently been made to this subject 

 •*■ through the Royal Society by Dr. W. Roberts and Prof. 

 Tyndall. Dr. Roberts's communication is as follows^ : — 



In a recent communication to the Royal Society, Dr. Bastian ^ 

 brought forward 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 pre- 

 viously neutralised or rendered alkaline by liquor potassoe, 

 especially if it be afterwards maintained at a temperature of 

 115° F. or 122° F. In this respect urine only conforms to the 

 general rule observed by myself and formulated in my previous 

 communication to the Society ^ — that " slightly alkaline liquids 

 were always more difficult to sterilise (by heat) than slightly 

 acid liquids." 



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 neutralised infusion 

 invariably becoming fertile after a similar boiling. Accordingly 

 I utilised hay-infusion to determine the cause of the difference in 

 question. It could evidently only be due to one of two things — . 

 either (l) the change of reaction enabled germs pre-existing in 

 the infusion to survive the ebullition ; or (2) the addition of the 

 alkali exercised a positive influence in exciting a de novo genera- 

 tion of organisms. To decide which of these two interpretations 

 was the true one, an experiment was contrived in which the 

 liquor potassse could be added to the infusion, not before, but 

 after it had been boiled, and thereby rendered permanently sterile. 

 When added in this way, I found that liquor potassse had not 

 any power to excite germination. The infusions invariably re- 

 mained barren when the alkali was added to them after they had 

 been sterilised. I therefore concluded that the effect of the 

 change of reaction consisted simply in enabling pre-existing 

 germs to survive a brief ebullition. Dr. Bastian, in repeating 

 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 promoting the origin of organisms in the urine. 



This experiment, if properly performed, is obviously a crucial 

 one, and it is recognised as such by Dr. Bastian. But two con- 

 ditions are essential to the validity 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, that in adding the liquor 

 potassse due care is taken that no new germs are introduced at 

 the same time. In repeating my experiment, Dr. Bastian ap- 

 pears to have departed from my procedure in two points, and he 

 has thus possibly laid himself open to the two sources of fallacy 

 just mentioned. In my own experiments, the acid infusion, after 

 it had been boiled, was set aside in a warm place for a fortnight 

 in order to test its sterility ; and the liquor potassse was not 

 added to it until the lapse of time had satisfied me that it had 

 been rendered permanently barren. In Dr. Bastian's experi- 

 ments the liquor potassse was added as soon as the vessels had 

 cooled, so that he had no certainty that their contents would not 

 have germinated without the addition of the alkali.* In the 

 second place, instead of heating the tubes containing the liquor 

 potassse (as I had done) to 150° F., and thus ensuring the de- 

 struction of all germs contained in the air imprisoned therein 



' " Note on the Influence of Liquor Potasss and an Elevated Temperature 

 on the Origin and Growth of Microphytes," by W. Roberts, M.D. Com- 

 municated by Prof. Tyndall, F.R.S., December 21, 1876. 



"Researches Illustrative of the Physico-Chemical Theory ot Fermenta- 

 tion," &c., read before the Royal Society, June 15, 1876. 

 3 Studies on Biogenesis. Phil. Trans, vol. Ixiv. p. 457. 

 i'i^ '*°' sufficient to rely in such a case on a central flask or retort. 

 Each flask or retort should have its own individual sterility tested, because 

 It IS practically impossible to apply the heat exactly in the same degree in 

 any two casos. 



with the alkali, he contented himself with subjecting them for 

 an inconsiderable period to the heat of boiling water. 



Seeing these two possible sources of fallacy, I determined to 

 repeat Dr. Bastian's experiments with urine, but taking care to 

 avoid these defects. I proceeded as follows : — 



A flask with a longish neck was charged with an ounce of 

 normal acid urine. The due quantity of liquor potasste requisite 

 to exactly neutralise this (as ascertained by previous trials) was 

 inclosed in a sealed glass tube drawn to a capillary portion at 

 one end. The tube was then heated in oil up to 280° F., and 

 maintained at that temperature for fifteen minutes. The tube 

 was then introduced into the body of the flisk. The neck of the 

 flask was next drawn to a narrow orifice ; then the urine was 

 boiled for five minutes, and the orifice sealed in ebullition. Ten 

 such flasks were charged and treated in the same manner. They 

 were then set aside in a warm place (from 70° F. to 80° F.) for a 

 fortnight. At the end of this time the contents of the flasks were 

 found perfectly transparent ; the urine was therefore assumed to 

 be permanently sterilised. The liquor potassse was then libe- 

 rated by shaking the tubes against the sides of the flasks and thus 

 breaking their capillary points. The previously acid and barren 

 urine was thus neutralised. The flasks were then placed in an 

 incubator and maintained at a constant temperature of 115" F. 

 At the end of two days it was found that the urine in each flask 

 had deposited a sediment of earthy phosphates, but the super- 

 natant liquor was perfectly transparent. The flasks were again 

 placed in the incubitor and maintained at a constant tempe -ature 

 of 122° F. for three days. At the end of this period they were 

 withdrawn and opened for examination. Not one of them 

 showed the slightest evidence of living organisms ; the super- 

 natant liquor was perfectly transparent, and no Microphytes 

 could be detected under the microscope. The precipitalel phos- 

 phate in some of the flasks presented a granular appearance, 

 which might, by the unwary, be mistaken for Micrococci, but 

 any such illusion was at once dissipated by adding a drop of 

 hydrochloric acid, which instantly dissolved the phosphate and 

 restored the perfect transparency of the urine. This acid has no 

 effect on the turbidity caused by Microphytes. 



These experiments therefore negative the conclusion that liquor 

 potassse, or a temperature of 115° F. to 122° F., or both con- 

 ditions combined, have the power of exciting the generation of 

 organisms in sterilised urine. 



The effect of elevated tem.perature was also tested in another 

 way. I had by me twenty-nine preparations of fermentible 

 liquids which had remained over from my previous experiments 

 in 1873-74. These consisted of 



15 alkalised hay-infusons, 

 5 pieces of boiled egg-albumen in water, 



1 piece of turnip in water, 



2 diluted ascitic fluid, 

 I blood with water, 



I albuminous urine, 



4 pieces of meat or fish in water. 



These had all been sterilised by the heat of boiling water two 

 or three years ago, and were contained in large bulbs with long 

 necks. Ten of the hay-infusions were hermetically sealed ; the 

 rest were all open to the air, under the protection of a plug of 

 cotton-wool. All possessed perfectly transparent supernatant 

 liquors, and showed no signs of containing organisms, nor of 

 having undergone any fermentive or putrefactive changes. 



These twenty-nine preparations were introduced into the incu- 

 bator, and maintained at a constant temperature of 115° F. for 

 two days, and then at a temperature of 122° F. for three days. 

 At the end of this period not one of them showed any signs of 

 fertility. The supernatant liquid in each bulb was quite trans- 

 parent, and some of them, which were opened for microscopic 

 examination, showed no traces of living organisms. 



I can, however, fully confirm the statement of Dr. Bastian, 

 that Bacteria, or certain kinds of them, grow and multiply freely 

 in (unsterilised) urine, both acid and neutralised, when exposed 

 to a temperature of 115° F. to 122° F. 



The following is Prof. Tyndall's paper 1 : — 



The communication " On the Influence of Liquor Potassa; and 

 an Elevated Temperature on the Origin and Growth of Micro- 

 phytes," which, at Dr. Roberts's request, I have had the pleasure 

 of presenting to the Royal Society, causes me to say earlier than 

 I should otherwise have done, that the subject which has occu- 



^ "Note on the Deportment of Alkalized Urine," by Prof Tyndall, 

 F.R. S, Communicated December 21, 1876. 



