[8] The sulphur bacteria are partially prototrophic for S; probably the iron bacteria also for Fe. Some few soil bacteria have been shown to be capable of utilizing free H, and it seems certain that the bacteria associated with the spontaneous heating of coal may oxidize free C. So far as known no elements other than these six are directly available to bacteria. [9] Only a few kinds of bacteria so far as known are proto-autotrophic. The nitrous and nitric organisms of Winogradsky which are so essential in the soil, and which might have been the first of all organisms so far as their food is concerned, and some of the sulphur bacteria are examples. [10] The term _pathogenic_ is also applied to certain non-parasitic saprophytic bacteria whose products cause disease conditions, as one of the organisms causing a type of food poisoning in man (_Clostridium botulinum_), which also probably causes “forage poisoning” in domestic animals. [11] The term “fermentation” was originally used to denote the process which goes on in fruit juices or grain extracts when alcohol and gas are formed. Later it was extended to apply to the decomposition of almost any organic substance. In recent years the attempt has been made to give a chemical definition to the word by restricting its use to those changes in which by virtue of a “wandering” or rearrangement of the carbon atoms “new substances are formed which are not constitutents of the original molecule.” It may be doubted whether this restriction is justified or necessary. A definition is at present scarcely possible except when the qualifying adjective is included as “alcoholic fermentation,” “ammoniacal fermentation,” “lactic acid fermentation,” etc. [12] See “Oil and Gas in Ohio,” Bownocker: Geological Survey of Ohio, Fourth Series, Bull. I, pp. 313-314. [13] It is probable that this is the way “Jack o’lanterns” or “Will o’ the wisps” are ignited. Marsh gas is produced as above outlined from the vegetable and animal matter decomposing in swampy places under anaërobic conditions and likewise phosphine. These escape into the air and the “spontaneous combustion” of the phosphine ignites the marsh gas. [14] Dr. H. H. Green, of Pretoria, South Africa, has isolated from “cattle dips” a bacterium that _reduces arsenates_ to _arsenites_. [15] Dr. Green (l. c.) has also isolated an organism which causes some deterioration of cattle dips by _oxidizing arsenites to arsenates_. [16] It will be noted that the names of enzymes (except some of those first discovered) terminate in _ase_ which is usually added to the _stem of the name of the substance acted on_, though sometimes to a word which indicates the substance formed by the action, as _lactacidase_, _alcoholase_. [17] Tetanus toxin is about 120 times as poisonous as strychnin, both of which act on the same kind of nerve cells.