The observations of Bienstock and numerous other bacteriologists have shown that the character of bacteria may be modified to an astonishing degree by a change of food or culture media ; that is, a change of the soil in which the bacterial plant grows, produces remarkable and characteristic changes in the character of the plant and of its products. One of the most notable facts is that most bacteria refuse to grow in the presence of acids. This is particularly true of disease-producing bacteria.
A few bacteria are able to resist acids. These are the organisms that give rise to fermentations, such as the souring of milk and the fermentation of solutions of sugar in the formation of vine-gar. The products of bacterial work are always poisonous to the organism by which they are produced. This fact limits the degree of acidity that can be produced by any particular organism.
The B. Bulgaricus is remarkable in possessing greater resistance to acids than any other micro-organism known. It will endure a concentration of acids as high as four per cent, whereas few other organisms can resist a concentration much greater than one per cent. This organism will continue to grow in a solution that contains thirty times the amount of acid which will stop the growth of Welch’s bacillus, an organism which produces foul gases in the intestine. It is chiefly because of its acid-forming activity that the B. Bulgaricus is able to render special service in efforts to change the intestinal flora, as will be shown later.
Sugar Loving Bacteria
Certain bacteria, like the nitrogen-fixing bacteria of the soil, require a large amount of carbohydrate. Malt sugar, milk sugar, dextrose and even cane and other sugars, are greedily seized upon by the sugar loving organisms, many of which are recognized by bacteriologists through the fondness which they show for particular forms of sugar. Sugars of various kinds furnish food par excellence for the bacteria that produce acid fermentation. Most of the colon bacteria are sugar loving organisms, a fact of great significance.
Protein Loving Bacteria
On the other hand, many bacteria thrive best when supplied with a culture media containing an abundance of nitrogenous substances in some form.
These organisms in turn give rise to a destructive change that in organic substances is commonly known as putrefaction. Instead of acids this class of bacteria produce ammonia, ptomains, skatol, indol, phenol, or carbolic acid, and other highly poisonous substances, among which are tox-albumins, which closely resemble and sometimes exceed in virulence the venoms of the most poisonous reptiles.
Some of these nitrogen loving organisms are able to decompose native or raw protein, while others are only able to successfully attack protein that has been partially broken down by the digestive process.
Animal Protein Most Readily Undergoes Putrefaction
Several years ago Doctor Tissier of the Pasteur Institute conducted a research for the purpose of determining The relative activity of these putrefactive bacteria upon animal and vegetable proteins. In a letter to the writer Tissier stated that in general proteins of animal origin are attacked twice as readily by putrefactive organ-isms as are proteins of vegetable origin. This fact is of great importance and agrees with the observation made by Combe many years ago, that brenzcatechin, a highly poisonous pigment that causes pigmentation of the skinso-called “liver spots”is produced only by the action of bacteria upon animal protein.
The Process of Decomposition
The decomposition of organic matter is not a simple process. There are two classes of sub-stances, those which ferment, carbohydrates, and those which decay, proteins. The two classes of bacteria, those that feed on sugar, causing fermentation, and those that decompose protein, causing decay, work together; but the fermentation process starts first because this class of organisms grows most rapidly. Even in meat there is sufficient sugar to start the fermentation process, and so the first symptom of decay in meat is souring. After the sugar is used up the acids are destroyed by germs that feed on them. At the same time, the process of putrefaction is slowly starting through the growth of the bacteria that feed on protein. Soon the acids disappear, ammonia takes their place, and the odors of putrefaction appear.