Where do they occur?

2) Найдите и переведите: а) условные придаточные предложения, кото­рые выражают маловероятные предположения; б) предложения с много­тачными глаголами shall, will, should, would.

Text В What are Bacteria?

Bacteria rule the world. Man is dependent upon them from the day of his birth until the hour of his death. They are man's most useful servants and his most destructive masters. One is prone to ask: What are bacte­ria? Where do they occur? What are their functions?

Bacteria are minute single-celled living beings devoid of roots, leaves and stems. They are so small that they can be seen only with the aid of a powerful microscope; They are often spoken of as microorganisms. This term includes not only bacteria but all forms of life so small that you should require the microscope in their study. They are often re­ferred to as germs or microbes. The early investigators considered them animals and would refer to them as «animalcules».

If we examined the bacteria we should find that they have many of the characteristics of animals. Some have the power of independent motion. All are devoid of green colouring matter, chlorophyll; most of (hem are compelled to live upon complex foods as do the animals. Their general structure, their methods of growth, their formation of threads and spores, and their simplicity in some of the lower forms of plant life, have caused the biologist to class them as plants. However, it is impos-

166 ♦ Learning to Understand a Medical Text

sible to make a clear-cut¹ distinction between some microscopical plants and some microscopical animals.^he important thing to remember is that.bacteria are the simplest forms of life, and partake of the character­istics of both plants and animals. For this reason, and for convenience, scientists agree to consider the bacteria with the plants.

Where do bacteria occur? Bacteria are widely distributed, occurring nearly everywhere. They are found in all natural soils, the number vary­ing with the kind of soil, quantity of plant and animal debris present, moisture and treatment. They decrease in number with depth. Although they occur in air, it is not their natural home as under ordinary condi­tions they cannot grow and multiply in it. The number and variety found in air vary. The atmosphere of some high mountains and the air over the ocean far from shore may be free from bacteria. City and country air also differ from each other in the number and kind of bac­teria which they contain. There is a great variation in the air of build­ings. Bacteria are especially numerous where dust is plentiful.

Most natural waters contain many bacteria. In sewage and polluted
waters² they are especially numerous. If measures against pollution and
contamination of water were not taken in time there would be much
danger to people's health. They occur only in small numbers or not at
all in deep wells³ and springs.⁴ A turbid stream, which contains the
drainage of many cities, has a great variety and number of bacteria in
opposition to the clear, rapid flowing water of uninhabited mountainous
regions. *

The intestines, owing to their alkaline reaction and the partly digested condition of their contents, are a great reservoir of bacteria. In the upper part there are few, but in the descending colon billions of bacteria are present. Sometimes they constitute one third of the total dry contents of the intestine. The health of the individual is determined by the number and kind of bacteria.

The normal tissues and the blood of animals are usually free from bacte­ria. If ordinary saprophytic bacteria entered the animal's body they would be ingested and destroyed by leukocytes. Microorganisms are rarely found on certain healthy mucous membranes, such as those of the kidneys, blad­der and lungs. Occasionally they pass through the skin or the mucous membranes of the digestive tract after which they may be found for a short time in the blood. In certain diseased conditions the blood and tissues of man and lower animals become filled with bacteria.

Functions of Bacteria. The real significance of bacteria comes in the fact that we are living in a world filled with them. They cannot be kept out of the

Lesson 14 ♦ 167

ilimentary tract. Considerable attention should be given to the favouring of i he beneficial bacteria in man. The great Russian bacteriologist Mechnikov i laimed that the rate with which man ages would be determined not by the \ cars he has lived, but by the bacteria, which inhabit his digestive system.

Notes

1. clear-cut четкий

2. sewage waters сточные воды

3. well колодец

4. spring источник

Упражнение 4. Найдите в тексте предложения, более полно выражающие мысль данных суждений.

1. Man is dependent upon bacteria. 2. Bacteria are very small. 3. Bacte­ria are often spoken of as microorganisms. 4. They have many characteris-lics of animals. 5. Some characteristics of bacteria have caused the biologist to class them as plants. 6. We are living in a world filled with bacteria.