The name Micrococcus Guignardi has been applied to more or less spherical bodies 2·2µ in diameter, also met with in silicified plants.
A portion of one of Renault’s figures is reproduced in Fig. 28 A. The faint and broken lines mark the position of the middle lamellae of parenchymatous cells from the pith of a Calamite. The tissue has been almost completely destroyed, but the more resistant middle lamellae have been partially preserved. The short and broad rods represent what Renault terms Bacillus Tieghemi; the small circle in the middle of some of these being referred to as a spore, and in one specimen shown in the figure, the second rod at right angles to the first is described as a small daughter-Bacillus formed by the germination of the central spore.
The isolated circles in the figure are referred to Micrococcus.
FOSSIL BACTERIA.
It is unnecessary to give an account of the numerous examples of Micrococci and Bacilli described by Renault from Devonian, Carboniferous, Permian and Jurassic rocks. We may, however, in a few words consider the general question of the existence and possible determination of fossil Bacteria.
In 1877 Prof. Van Tieghem[218] of Paris drew attention to the method of operation and plan of attack of Bacillus amylobacter as a destructive agent in the decay of plant débris in water. He was able to follow the gradual disorganisation of the tissues and the various steps in the ‘butyric fermentation’ effected by this Bacterium. Similarly the same author[219] was able to detect the action of an allied organism in some silicified tissues from the Carboniferous nodules of Grand-Croix, a well-known locality for petrified plants near Saint-Étienne. He recognised also the traces of the Bacillus itself in the partially destroyed plant tissues. The Palaeozoic Bacteria made use of some cellulose-dissolving ferment of which the action is clearly demonstrated in sections of silicified tissues. Many of the phenomena described by Renault and Bertrand as due to similar Bacterial action, afford additional evidence that the gradual disorganisation of vegetable tissues was effected in precisely the same manner as at the present day.
In some cases we have I believe trustworthy examples of the Bacteria themselves, both in coprolites and plant-tissues, but it is more than probable that some of the recorded examples are not of any scientific value. The examination of petrified tissues under the higher powers of a microscope often reveals the existence of numerous spherical particles and rod-like bodies which agree in shape with Micrococci or Bacilli. Minute crystals of mineral substances may occur in the siliceous or calcareous matrix of a petrified plant which simulate minute organic forms. Vogelsang[220] in his important work die Krystalliten has thrown considerable light on the ontogeny of crystals, and the minute globulites and other forms of incipient crystallisation might well be mistaken for Bacterial cells. Granting, however, that we have satisfactory evidence, both direct and indirect, that some forms of Bacteria lived in the decaying tissues of Palaeozoic plants, and in the intestines of reptiles and other animals, we cannot safely proceed to specific diagnoses and determinations[221].
Renault has pointed out that fossil Bacteria may often be more readily detected than living forms owing to the presence of a brown ulmic substance which results from the carbonisation of the protoplasm. He is forced to admit, however, that such diagnostic characters as are obtained by Bacteriologists by means of cultures cannot be utilised when we are dealing with fossil examples! We are told that “Partout où nous avons cherché des Bacteriaceés, nous en avons rencontré.”[222] This indeed is the danger; an extended examination of fossil sections under an immersion-lens must almost inevitably lead to the discovery of minute bodies of a more or less spherical form which might be Micrococci. To measure, and name such bodies as definite species of Micrococci is, I believe, but wasted energy and an attempt to compass the impossible.
Specialists tell us that the accurate determination of species of recent Bacteria is practically hopeless: may we not reasonably conclude that the attempt to specifically diagnose fossil forms is absolutely hopeless? “The imagination of man is naturally sublime, delighted with whatever is remote and extraordinary—”, but it is to be deplored if the fascination of fossil bacteriology is allowed to warp sound scientific sense.