112 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



lished any subsequent investigators should have 

 abandoned it in favor of a less exact mode of ex- 

 perimentation. 



No maintainer of the theory of spontaneous 

 generation would deserve a hearing if he refused 

 to subject his experiments to the conclusive test 

 afforded by a method which, with ordinary care, 

 is known to be infallible ; and germ - theorists 

 would be fairly justified in rejecting all adverse 

 experiments performed with no better safeguards 

 than bent tubes or plugs of cotton-wool. The 

 stranjre thins; is that the severe condition of her- 

 metically sealing has been self-imposed by Bastian 

 and most other supporters of the de novo origin 

 of life, while Pasteur, the great champion of the 

 germ-theory, and many of his disciples (Tyndall 

 among the rest), have generally been content to 

 use less stringent methods. The consequences 

 which have flowed from the extraordinary indul- 

 gence thus extended by these savants to their 

 adversaries will be seen when we review a few 

 of the most important scries of experiments relied 

 on upon either side. But for the present it is 

 enough to note that neither of tile first two funda- 

 mental conditions of the crucial experiment is be- 

 yond the resources of science. By applying suf- 

 ficient heat dead matter may be obtained. By 

 hermetically sealing the glass vessel which con- 

 tains it the condition of perfect isolation may be 

 secured. 



The remaining steps in the investigation are 

 comparatively free from difficulty. If the experi- 

 ment is performed on suitable materials we know 

 empirically under what conditions of temperature, 

 concentration, and the like, life is most wont to 

 appear, though absolute uniformity of result can- 

 not always be predicted. Under some conditions 

 it is found that life is invariably developed. Un- 

 der other conditions it will frequently show itself. 

 With yet other conditions its manifestation is ex- 

 tremely rare ; while in others, again, its non-ap- 

 pearance maybe almost certainly predicted. For 

 the purpose of fully investigating the laws of life- 

 evolution such limited knowledge as this would 

 be far short of what is needed. But in order to 

 solve the simpler question, whether life can, under 

 any circumstances, arise without the presence of 

 previously-living germs, it is amply sufficient. The 

 last step of all in the inquiry was once supposed 

 to present difficulties of the most serious kind. 

 When one observer declared that he had found 

 living things in a fluid which he had examined, it 

 was quite a matter of course for his critics to 

 suggest that what he had seen consisted of noth- 

 ing but dead matter. It was not always easy to 



answer such objections, for the ordinary test of 

 life is motion, and in the field of the microscope 

 dead particles may simulate to some extent the 

 movements of life. It is true that no observer of 

 any experience could fail to discriminate between 

 these Brownian movements, as they are called, 

 and the active, darting motions of lively bacteria 

 or monads ; but still the doubt was so easy for 

 an outside caviler to suggest, and it was so hard 

 for a solitary worker to prove that he had not 

 misinterpreted what he saw, that a haze of uncer- 

 tainty was apt to rest on experiments dependent 

 on such observations. Fortunately, this source 

 of skepticism has been dried up. A much better 

 test of life than motion is now almost always relied 

 on — the power of multiplication. In all the experi- 

 ments made with a view to try the truth of the 

 rival theories we are considering, the particular 

 form of life which is developed is that which ac- 

 companies ordinary putrefaction or fermentation, 

 and it is now quite established that where putre- 

 faction or fermentation is going on, life, in the 

 shape of swarms of rapidly-multiplying bacteria, 

 torulae, or analogous organisms, may be assumed 

 to be present. The question, in fact, has passed 

 out of the range of the microscope. If a trans- 

 lucent organic fluid is seen to gradually grow tur- 

 bid and putrefy, there is no need of a microscope 

 to prove that the opalescent or turbid cloud is 

 composed of a teeming mass of microscopic organ- 

 isms. In doubtful cases of scarcely perceptible 

 turbidity the microscope is often appealed to with 

 success, and may always be used for confirmation. 

 But in the great majority of cases the unassisted 

 senses suffice to determine the presence or ab- 

 sence of life. 



Enough has been said to demonstrate the 

 feasibility of experiments decisive of the great 

 issue raised in the cause of Spontaneous Genera- 

 tion vs. Germ Theory. It remains to consider 

 how the balance of evidence inclines at present. 

 Within the compass allotted to an article in these 

 pages it would be impossible to discuss or even 

 refer to a tithe of the experiments which have 

 been performed with a view to elucidate the sub* 

 ject under consideration. A rather severely-re- 

 stricted selection becomes a necessity, and it \3 

 very important that the selection should be gov- 

 erned by some fair and just principle. And the 

 first consideration clearly ought to be given to 

 the experiments which, from the conditions under 

 which they were performed, are entitled to the 

 greatest weight. The great bulk of scientific work 

 is almost of necessity conducted in solitude or in 

 the presence only of subordinate assistants, and 



