The browning of cut apples is known to be due to the action of an oxydase, that is, an oxygen carrying ferment, and the same is claimed for the deep colouring of certain lacs obtained from the juice of plants, such as Anacardiaceæ, which are pale and transparent when fresh drawn, but which gradually darken in colour on exposure to the air. Oxydases have been isolated from beets, dahlia, potato-tubers, and several other plants. This fact explains a phenomenon known to botanists, and partly explained by Schönbein as far back as 1868, that if certain fungi (e.g., Boletus beridies) are broken or bruised, the yellow or white flesh at once turns blue; this action is now traced to the presence in the cell sap of an oxydase.
It is the diastatic activity of Aspergillus which is utilised in the making of saké from rice, and in the preparation of soy from the soja bean in Japan. Katz has recently tested the diastatic activity of Aspergillus, of Penicillium, and of Bacterium megatherium, in the presence of large and small quantities of sugar, and found all are able to produce not only diastase, but also other enzymes; as the sugar accumulates the diastase formed diminishes, whereas the accumulation of other carbo-hydrates produces no such effect. Harting’s investigation on the destruction of timber by fungi derives new interest from the discovery of an emulsion-like enzyme in many such wood-destroying forms, which splits up glucosides, amygdalin, and other substances into sugar, and that hyphæ feed on other carbo-hydrates. The fact, also, that Aspergillus can form inverts of the sucrase and maltase types, as well as emulsin, inulate, and diastase, according to circumstances of nutrition, will explain why this fungus can grow on almost any organic substance it may happen to alight upon. The secretion of special enzymes by fungi has a further interest just now, for recent investigations promise to bring us much nearer to an understanding of the phenomena of parasitism than it was possible when I was at work upon them some forty or fifty years ago.
It was De Bary who impelled botanists to abandon older methods, and he who laid the foundation of modern mycology. Later on he pointed out that when the infecting germinal tube of a fungus enters a plant-cell, two phenomena must be taken into account, the penetration of the cell-walls and tissues, and the attraction which causes the tips of the growing hypha to face and penetrate these obstacles, instead of gliding over them in the lines of apparent least resistance. The further development of these two factors shows that in the successful attack of a parasitic plant on its victim or host these fungi can excrete cellulose-dissolving enzymes, and that they have the power of destroying lignine. Zopf has also furnished examples of fungi which can consume fats. There is, however, one other connection in which these observations on enzymes in the plant-cell promise to be of considerable importance, viz., the remarkable action of certain rays of the solar light on bacteria. It has been known for some time past that if bacteria in a nutrient liquid are exposed to sunlight they quickly die. The further researches of Professor Marshall Ward and other workers in the same direction have brought out the fact that it is really the light rays, and not high temperatures, that it is especially the blue-violet and ultra-violet rays, which exert the most effective bactericidal action. This proof depended upon the production of actual photographs in bacteria of the spectrum itself. Apart from this, the Professor demonstrated that just such spores as those of anthrax, at the same time pathogenic and highly resistant to heat, succumb soonest to the action of these cold light-rays, and that under conditions which preclude their being poisoned by a liquid bath. It is in all probability the action of these rays of light upon the enzymes, which abound in the bacterial cells, that bring about their death.
The sun, then, is seen to be our most powerful scavenger, and this apparently receives confirmation in connection with Martinaud’s observations, that the yeasts necessary for wine-making are deficient in numbers and power on grapes exposed to intense light, and to this is due that better results are obtained in central France as contrasted with those in the south. “When we reflect, then, that the nature of parasitic fungi, the actual demonstration of infection by a fungus spore, the transmission of germs by water and air, the meaning and significance of polymorphism, heteræcism, symbiosis, had already been rendered clear in the case of fungi, and that it was by these studies in fermentation, and in the life-history of the fungus Saccharomyces, that the way was prepared for the ætiology of bacterial diseases in animals, there should be no doubt as to the mutual bearings of these matters.”
Industrial uses of Fungi and Saccharomycetes.
There are many industrial processes which are more or less dependent for success on bacterial fermentations. The subject is young, but the results already obtained are seen to be of immense importance from a scientific point of view, and to open up vistas of practical application already being taken advantage of in commerce, while problems are continually being raised by the forester, the agriculturist, the gardener, the dairyman, the brewer, dyer, tanner, and with regard to various industries, which will eventually confer great advantages in their economic application.
The remarkable discovery made by Alvarez of the bacillus, which converts a sterilised decoction of the indigo plant into indigo sugar and indigo white, the latter then oxidising to form the valuable blue dye, whereas the sterile decoction itself, even in presence of oxygen, forms no indigo, plainly proves how these minute organisms may be turned to a good account. There are, however, important points to be determined as to the action of the fermentation brought about by these enzymes, and the appearance of certain mysterious diseases in the indigo vats. Again, certain stages in the preparation of tea and tobacco leaves are found to depend upon very carefully regulated fermentations, which must be stopped at the right moment, or the product will be spoilt. Regarding the possible rôle of bacteria, the West Indian tobacco has a special bacterium, which has been isolated and found to play a very important part in its flavour. Every botanist knows that flax and hemp are the best fibres of Linum and Cannabis respectively, separated by steeping in water until the middle lamella is destroyed and the fibres isolated; but it is not so well known that not every water is suitable for this “retting” or steeping process; and for a long time this was as much a mystery as why some waters are so much better than others for brewing. Quite recently Fribes has succeeded in isolating the bacillus upon which the dissolution of the middle lamella depends. This investigation brought out other interesting details as to the reaction produced by living micro-organisms, and which can be utilised in deciding questions of plant chemistry too subtile for testing with ordinary re-agents. One other important fact connected with these researches is that botanists have now discarded the view that the middle lamella of the plants referred to is composed of cellulose, and know that it consists of pectin compounds. Fribes’ anærobic bacillus is found to dissolve and destroy pectins and pectinates, but does not touch cellulose or gum. It is well known that the steeping of skins in water in preparation for tanning involves bacterial action, owing to which the hair and epidermal coverings are removed, but it also appears that in the process of swelling the limed skins, the gases evolved in the substance of the tissues, and the evolution of which causes the swelling and loosens the fibre so that the tanning solutions may penetrate, are due to a particular fermentation caused by a bacterium, which, according to some investigators, is identical with a lactic ferment introduced by the pine bark, and which is responsible for the advantageous acidification of the tanning solutions.
Hay is made in different ways, and in those where a “spontaneous” heating process is resorted to the fermentation is no doubt dependent upon the presence of thermogenic bacteria. But probably no other subject has attained to so much importance as the bacteriology of the dairy: the study of the bacteria found in milk, butter, and cheese in their various forms.
Of milk, especially, much has been written and said as a disease-transmitting medium, and with every good reason, and, if the statement of a Continental authority may be accepted that each time we eat a slice of bread and butter we devour a number of bacteria equal to the population of Europe, we have sure grounds for seeking for further information as to what these bacteria are and what they are doing. And similarly so with cheese, which teems with millions of these minute organisms.
“Some few years ago it was found that the peculiar aroma of butter was due to a bacterium. There are two species of bacteria, one of which develops an exquisite flavour and aroma, but the butter keeps badly, while the other develops less aroma, but the butter keeps better. In America, however, they have isolated and distributed pure cultures of a particular butter bacillus which develops the famous ‘June’ flavour, hitherto only met with in the butter made in a certain district during a short season of the year. This fine-flavoured butter is now constantly manufactured in a hundred American dairies; and the manufacture of pure butter with a constant flavour has become a matter of certainty.