856 GENERATION. 



Now, what degree of temperature is required, what is the duration of exposure to heat 

 necessary to destroy germs, and how are the limits of these conditions to be ascertained? 

 The only answer to this question lies in the experimental test. When infusoria make 

 their appearance in solutions that have been exposed to heat and protected from the 

 entrance of germs, it is said that the heat has not been sufficiently high or the exposure 

 has been of too short duration. When infusoria do not appear, the conditions are 

 assumed to have been fulfilled. This mode of reasoning assumes the fact, from the begin- 

 ning, that there is no such thing as spontaneous generation. Suppose, now, we start 

 with the contrary assumption, that there may be spontaneous generation in an organic 

 infusion. We admit to such an infusion, air, carefully purified from germs, which is 

 logically an essential experimental condition ; we have previously exposed the infusion 

 to a high temperature for a certain period. Under these conditions, no infusoria appear. 

 It may then be assumed that the heat has destroyed the properties of the organic mole- 

 cules, so that they cannot come together and generate new beings. 



Under these circumstances, all that we can do is to argue logically from such facts as 

 have been positively established, and to take the most reasonable view of other points, 

 that are not as yet capable of satisfactory and definite explanation. 



We shall assume that it has been demonstrated, beyond a reasonable doubt, that, in 

 organic infusions, subjected to a temperature somewhat above that of boiling water, and 

 supplied with air that has been effectually deprived of organic matter, ova, spores, or 

 whatever it may be, no living organisms make their appearance so long as these experi- 

 mental conditions are maintained. We also assume that simple boiling, at 212 Fahr., 

 does not necessarily destroy all germs, which excludes experiments made in this way. 

 This reduces the question to a single, simple point : In infusions in which the organic 

 matter has not been destroyed by heat, do the living organisms come from a spontaneous 

 aggregation of organic molecules, or are they the result of the development of ova? 



In the case of the very lowest organisms making their appearance under these con- 

 ditions, they are themselves so small, that it would be reasonable to suppose that we 

 might be unable to see the ova, assuming that they exist. The organic particles that are 

 supposed to come together spontaneously are also invisible, even under the highest mag- 

 nifying powers at our command. If we come to an exact definition of the term spon- 

 taneous, we may say that it means an action " arising or existing from natural inclination, 

 disposition, or tendency, or without external cause " (Worcester). With this definition, 

 the statement that a living organism is generated spontaneously can only mean that there 

 is no cause that can be assigned for its production. In point of fact, we simply acknowl- 

 edge that the mode and cause of generation of certain infusoria are unknown, and the 

 history of our knowledge of generation shows that the term spontaneous generation has 

 always been applied to the production of beings in a manner that is incapable of satis- 

 factory explanation. What we actually know of the mode of generation of animal organ- 

 isms teaches us that all beings are produced and multiplied by ova, or by processes of 

 segmentation or budding of preexisting organisms ; and our knowledge of these processes 

 now extends to all except the most minute infusoria, which have no apparent structure. 

 We know, also, that such organisms may develop in pure water from particles floating in 

 the atmosphere ; and that particles in the air, singly invisible, may be developed into 

 infusoria that are quite highly organized. If we reason that the products of so-called 

 spontaneous generation are formed by the fortuitous aggregation of organic molecules, 

 we assume a fact of which we have no other example in Nature; and we assume, also, 

 that such an aggregation of particles produces beings of a definite and uniform character. 

 For such a supposition, we have no basis in analogy. If, on the other hand, we regard 

 these low orders of beings as produced by the development of invisible germs, which 

 have found favorable conditions of heat and moisture, we rest upon a basis of reasonable 

 analogy, and we merely confess that this is a form of generation, the processes of which 

 are not as yet capable of demonstration. 



