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458 of these, and the development of bacteria is inevitable. The inference is that the motes are germs. The above experiments show that, in closely allied septic organisms, the germs of which have been demonstrated and their developments watched, if the dry débris of a maceration in which these forms are found be scattered in the air around a prepared fluid, and demonstrated by similar optical means, the said organisms develop; but if the minute dust from the débris be optically proved to be absent, none of the monad-forms appear. Here we do not hypothecate a germ, but we know that it exists; and its deportment in similar conditions is identical with that of the assumed bacterial germ. Do we need more irresistible evidence that the bacteria develop, not de novo, but from genetic products?

Evidently Dr. Bastian thinks we do. He tells us in effect that, if Dr. Tyndall has not succeeded, others have, in seeing bacteria reappear in infusions that have been exposed to a boiling-heat for five minutes. This is true; but not to the extent nor with the meaning Dr. Bastian claims. He furnishes a list in Nature, for example, of those who are supposed to have secured the results he insists on. But this list is, perhaps hastily, but in effect, most unjustly framed. It is not surprising to see strong protests from the investigators concerned. The citing of Roberts, for example, or Lankester and Pode, or Pasteur or Schwann, is simply a meaningless exercitation to all but the ignorant. Stripped of all disguise, the number of cases of the appearance of bacteria in sealed infusion after five or ten minutes' boiling is few and doubtful indeed. But still there are cases, and in one instance at least admirably attested; but they are confessedly exceptional in a high degree. Dr. Bastian, however, prefers to interpret Nature from the exceptional flasks, and infer "spontaneous generation" rather than be guided by the cumulative and overwhelming evidence of the existence of bacterial germs, as the medium of their normal reproduction. This must mean either that he believes that these organisms originate de novo as well as by germs, which is a direct petitio principii; or else that he is incapable of seeing the force of the facts which render the existence of germs inevitable. From the conflicting evidence of his own writing it would almost appear that he endeavored to maintain both these views. He has recently said, "Prof. Tyndall's results, admirable as they may be in themselves, are altogether collateral, and do not bear upon the main point at issue" Surely the "main point at issue" is the mode of origin of bacteria, and we cannot get much nearer the origin of an organic form than by tracing it to a genetic product—a spore! This was originally Dr. Bastian's question did bacteria originate de novo, or from parents? It is not so now. He says, "The question is, not