The microscopic organisms commonly called bacteria are also known in the popular mind as germs, microbes, micro-organisms, bacilli, and micro-cocci, while a New York magazine recently called them bugs. In the middle of the 19th century they were known only to a few experts and were looked upon as curiosities of the micro-scope, chiefly interesting for their large numbers, minuteness and activity. No one dreamed of them being of importance to man. Now we have entire laboratories solely for their study and large libraries devoted to this one subject.
For our purpose it is not necessary to go further than to classify the great number of bacteria of importance to the life and health of man into two simple groups: the coccus (plural cocci) of a round, ovoid form; the bacillus (plural bacilli, Latin diminutive for rod), generally of a rod-shaped or elongated form, varying much in shape and size. Thus the twisted rods are called spirilla. They divide transversely and may be found in threads or chains. These cocci and bacilli (cocci and ‘cilli for short) are embraced under the name bacteria which is the general term used when speaking of micro-organisms.
Bacteria, usually thought of by the layman as living microscopic animal organisms, are in fact classed as plants. Kendall says, however, they exhibit several prominent characteristics which suggest relationship with the lowest animals. The most important of these is the absence of chlorophyl (the green coloring matter of plants). This indicates very clearly their dependence on preformed food and implies an analytical or destructive function. One of the achievements of the Great War is a noteworthy advance in the science of bacteriology. This is manifested not only in marked improvements in methods of investigation and in modifications of pre-existing views in the important fields of infection and disease prevention, but also in a complete revision of some of the more important groups of bacteria.
Bacteria are structurally the simplest known organisms which maintain an independent existence. All their vital functions are exhibited in a single asexual (non-sexual) cell, devoid of a definite nucleus (central point). Re-production is by division. Successive generations may appear at intervals as frequent as every fifteen minutes. Many bacteria may, however, require hours or even days to arrive at maturity. Many living on dead or decaying organic matter form spores (corresponding to seeds in plants) for the continued vegetative growth of the organism. Spores have been dried and kept in a cool place for more than twenty years and yet when placed in a favorable environment developed anew with their usual luxuriousness. Practically, the average duration of life of bacteria is comparatively brief, from a few hours for gonococcus (the specific organism of gonorrhea, a sexual disease) to two or three months for the bacillus of tuberculosis. They may be frozen solid and kept in that condition for weeks without killing all the individuals. At the end of four weeks 95 per cent of frozen typhoid bacilli have succumbed. From four to six months’ continuous freezing is required to kill all of them. Many bacteria which are killed by an exposure of from one to two hours of direct sunlight in summer require an exposure of from two to three hours in winter. A single red human blood corpuscle weighs about 0.00008 of a milligram, (8-100,000 of the smallest measure of weight in the metric system) which is fifty thousand times the weight of a single colon bacillus .
Many kinds of bacteria may theoretically find conditions well adapted to their rapid development (in the intestine) and it is not surprising to find that bacterial proliferation (development by offshoots) is greater in both nature and extent in the intestinal tract than in any other known medium. It has been estimated that the aver-age daily fecal excretion of bacteria from a healthy adult on a normal diet is expressed by the truly enormous number of 33 x 1012 (multiply 10 by itself 12 times and that by 33). The upper level of the intestinal tract, particularly the duodenum (the upper section of the small intestine) , is relatively free from them during interdigestive periods. They increase rapidly as food enters the duodenum and decrease when the food passes to lower levels. The number increases very greatly where stasis (delay) of food becomes more marked and in the cecum and large intestine they are continually present in enormous numbers. The majority of these organisms, however, particularly the coccal forms, are to be regarded as opportunists they do not initiate disease as a rule. They are to be regarded as Theobald Smith has called them “organisms of the diseased state,” because of their invasion of the body secondary to other diseases. Even the tubercle bacillus and the diphtheria bacillus, particularly the latter, have been found in the mouths of men who apparently have had neither tuberculosis nor diphtheria, yet these organisms appear to be virulent when tested in the usual manner, and presumably might be able to incite disease whenever conditions favor their entrance to the tissues of the body that are, owing to debility or other causes, in a proper state of receptivity .
The idea that prevails in many quarters that bacteria are an evil that must be endured is erroneous. They are not only generally regarded as belonging to the vegetable order but their function throughout nature is very generally beneficent and essential to life. In the human organism, for instance, the meats and other proteid foods are broken down by them (catalysis) and by such decomposition the food is made available for the usees of the body. Each kind of food reacts to its own variety among these organisms.
Putrefaction and fermentation are physiologically two important and interesting words, intimately associated with digestion and constipation, that are frequently misused. Putrefaction represents a form of bacterial activity (decomposition) related to protein material (food de-rived in the main from animal sources) ; fermentation, to starches, sugars and closely-related compounds (carbohydrates). A most interesting fact, says Howell, is that each food element has its own digestive ferment (enzyme). The enzymes that act on carbohydrates are not capable of affecting the proteins and fats and vice versa. So in the fermentation of closely related bodies such as maltose (sugar derived from starch by the action of diastase or malt), sugar of milk (lactose) and common cane sugar, each requires seemingly its own specific digestive ferment, or enzyme. Each ferment seems adapted to act upon or become attached to the smallest quantity or unit of a substance that can exist separately with a certain definite structure (molecule) and is fixed to it, in fact, as a key to its lock.
This word enzyme was first applied to phenomena indicated .by bubbles of gas, as in alcoholic fermentation, in which alcohol is formed from sugar; the acid fermentations, as in the. souring of milk; and the putrefactive fermentations by which animal substances are disintegrated. The brilliant work of Pasteur established the fact that fermentations in the old sense are due to living organisms, which led to the present day classification, the grouping of ferments into two great groups: the living or organized ferments, such as yeast cells, bacteria, etc.; and the non-living or unorganized ferments such as pepsin, trypsin, etc. These latter came to be generally designated as enzymes. Later discoveries, how-ever, clearly indicate that there is no essential difference between living and non-living ferments? The underlying physical causes of fermentation, like many other mysteries of Nature, are not yet worked out and may never be.