Thus, in accordance with this latter view, living ferments are not needed--mere dead, organic or nitrogenous matter suffices to initiate the processes in question.[11] Those who hold this opinion may or may not believe that organisms are capable of arising _de novo_;[12] though there can be little doubt that a belief in the truth of such a doctrine does, almost inevitably, entail a belief in the _de novo_ origination of living things. No one who has looked into the evidence, doubts the fact of the association between some of these processes and the presence of organisms; the only question is, as to the relation in which they stand to one another. If organisms are not the causes of those fermentative changes with which they are invariably associated, then they are, in all probability, the results of such changes; and they must certainly have been produced _de novo_ if it can be shown that fermentation or putrefaction may take place under the influence of conditions which make it certain that pre-existing living organisms could have had nothing to do with the process. [11] Those who hold this opinion do not of course deny that living ferments can initiate fermentations. Every-day experience convinces them of the truth of this. They merely affirm that the intervention of vital action is not essential: they look upon fermentation as a purely chemical process, and believe that even in those cases where fermentation is initiated by living organisms (such as beer-yeast), these--although living--act chemically upon the matter which undergoes fermentation. [12] They may not believe this, because they may be unaware of the fact of the invariable association of some organisms with some kinds of fermentations, and may consequently have never concerned themselves with the evidence bearing upon this part of the question. (See Gerhardt, _loc. cit._)