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Bacteria

time, spores, organism, bacilli, mikros, bacillus, sometimes, mass and organisms

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BACTERIA.

The name infusoria was applied to the organ isms discovered by Leenwenhoeck, but the much more minute living things rendered visible by more powerful lenses were up to a late period all classified under the term Bac teria, which is a Greek word (baherion) mean ing a little staff.

Their excessive smallness is beyond one's power to imagine. Under the highest power of improved microscopes, which magnify about 4000 times, they appear like the periods and commas of ordinary type. If a man could be magnified by the same amount he would appear as huge as Mont Blanc or Chimborasso. Inn comparison to the size of an ordinary man a bacterion is as a grain of sand to Mont Blanc.

Workers with the microscope were not long in discovering that even among these smallest forms of life there was as great variety as among higher and larger forms. Indeed differ ences which they manifested were too great to permit them to be placed all together as mem bers of the same class or order. Various classi fications have been proposed for them, which it is unnecessary to state here. It is desirable, however, to note and remember several of the chief types. The differences which exist be tween them are largely in size and form, to some extent in mode of multiplication. In one thing they all agree. They all consist of a kind of protoplasm, a jelly-like substance, which is clear and transparent, without any indication whatever of separation into organs, but ex hibits sometimes fine granules. The proto plasm is inclosed by a membrane, which may be very dense and impenetrable, and capable of resisting the action of acids and alkalies and of heat and cold.

All the various kinds are grouped together as micro-organisms (Greek, mikros, microzymes (mikros, and ;Time, yeast), or microphytes (mikros, and phuton, a plant), Bacteria is also a general name for the special group which we are considering.

That group of micro - organisms — the Bac teria—consists of three chief types: 1. The micrococcus, or round organism; 2. The bacillus, or rod-shaped organism ; and 3. The spirillum, or spiral organism.

The Micrococcus (mikros, and kokkos, a berry) is round, and sometimes no larger than the 32,000th of an inch in diameter. It grows after a fashion common to the other forms. The body becomes narrowed in the middle, as if by a band tied round it. The constriction increases until the single round body is almost divided into two. In a brief time the connect ing thread is severed and the organism is completely split into two, each of which now has an independent existence. In a short time each one of the two divides, so that from the original one there are now produced four. This process of multiplication is called fission. Different kinds tend to divide in different directions. One kind dividing only in one direction forms chains --streptococci; another growing by division in several directions forms grape - like clusters— staphylococci; another dividing regularly in three directions forms masses like bales of cotton tied lengthways and across — sarcinae; and sometimes they develop in pairs—diplococci. Sometimes they

form masses, held together and embedded in a jelly-like substance—zooglcea mass.

The Bacillus ( Latin, bacillum, a little rod ) is rod-shaped, about of an inch long, and a third less in breadth, and it has rounded ends in some species and blunt ends in others. Some of them are provided with fine tail-like processes, one or more at each end, by the lashing movement of which they may move from place to place in fluids. It multiplies like the micrococcus by dividing. The process is shown in Fig. 198, c. When the division of one into two is almost complete, only a long thread connects the two halves. This finally breaks in the middle, and each half moves away as an independent being. Dallinger has shown that, besides growing in numbers in this way, they may multiply in another fashion. He has watched two organisms meet and be come fused together into one mass, losing their tails and becoming motionless. After a time the mass looks very granular. Filially it bursts, and there pours out a cloud of exceedingly fine particles. After watching the cloud of par ticles for some time Dallinger saw fully-formed organisms issuing from it. In fact the particles were spores or seeds, which, in a sufficient time, with the aid of heat, moisture, and nourishment, developed into the adult forms. This is multi plication by spore formation. In two ways, therefore, bacilli multiply. Bacilli are particu larly apt to form long chains or threads, being strung on end to end as they increase in num bers. Fig. 199, A 1, shows three bacilli. At 2 is seen a chain. In the body of each bacillus is seen a bright oval dot. This represents a seed or spore. It increases in size at the expense of the jelly-like material forming the substance of the organism, till it bulges out the inclosing membrane. At last the membrane bursts, and the spore is discharged. If it is surrounded by nourishing material it will develop into the full-grown bacillus. If not so favourably placed it may still retain its vitality. In fact spores may be exposed to all kinds of unfavourable con ditions—to cold or to heat ; they may become dry and be dispersed as dust. But let this ap parently lifeless dust be brought into favourable conditions of moisture and warmth, with nour ishment at hand, and forthwith the spores will grow, and adult forms will be produced from them in abundance. Fig. 199, n, shows bacilli with spores, and a mass of spores.

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