Hudson. — On Spontaneous Generation. 183 



belief in spontaneous generation is pretty general ; when organisms appear 

 in situations where they are nOt expected, and under ciruumstances which, 

 to a superficial observer, would appear calculated to exclude them, the 

 easiest mode of accounting for their presence is to assume that " they came 

 of themselves "; and, by way of parenthesis, I will say here that, when we 

 wish to account for or explain observed facts, we are always right to take 

 the simplest theory, provided such theory does not clash with any other 

 known facts. 



The possibility of organisms having a spontaneous origin has been 

 narrowed and narrowed by successive observers, until it is only the Bacteria 

 which at the present day are presumed, under certain conditions, to arise 

 spontaneously. These Bacteria are exceedingly minute rods and spheres 

 that invariably appear wherever decomposition of animal or vegetable 

 matter is going on. For instance, suppose we take any organic infusion 

 such as can easily be made by soaking a piece of meat, or hay, or turnip in 

 water for an hour or so ; we strain off the clear liquid and set it on one side. 

 If we examine it after a few days (a week or ten days in winter, a couple of 

 days in summer), we shall find that the clear liquid has become turbid, 

 and that it begins to smell offensive, — in common parlance it has turned 

 bad, or decomposed ! Why has it decomposed ? Modern science tells us 

 that organic matter cannot decompose without the presence and help of 

 Bacteria of some kind or other ; that a complex organic infusion, provided 

 we rigidly exclude germs, will remain as stable as a solution of sulphate of 

 copper. We have a practical application of the principle in the various 

 tinned meats. The germs in or on the meats or fish are first killed by 

 exposure to a high temperature, and then the tins are hermetically sealed so 

 as to exclude air, or rather germs ; for it is not the air that does the harm. 

 How can we prove this ? 



I have here three glass tubes, which I will call Nos. 1, 2, and 3. Some 

 months ago I put into each of these tubes some chopped hay and water. 

 No. 1 I left untouched in a sheltered place but exposed to air and light ; 

 No. 2 I boiled ; into No. 3 I inserted a cotton wool cork, quite permeable to 

 air, but which has been found to act as a sieve to Bacteria and their germs, 

 and then I boiled it for about five minutes. The steam issued freely from 

 the cotton wool, demonstrating its perfect permeability to vapour and air. 

 After four days I looked at the tubes. No. 1 appeared clear, No. 2 distinctly 

 turbid, No. 3 clear. A drop of No. 2 placed under the microscope showed 

 numerous rod-like Bacteria. The earlier appearance of turbidity in No. 2 

 is easily explained by the boiling having made the infusion quicker (and so 

 prepared the fluid for the reception and growth of germs) than the cold 

 water did. At the end of a week I examined the tubes a second time. Nos, 



