Для этой цели; 2) полный покой; 3) распространяется по коре головного мозга; 4) имеет большое защитное значение для; 5) глубокий спокойный сон; 6) жизнедеятельность.

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The nervous cells of the cortex are the most delicate of all the cells of the human body.

It is at the moment of tiredness of the cortical nervous cells that the process of inhibition begins to act. This process does not allow new stimuli to pass to the tired areas of the brain. To provide the smooth work of the brain the nervous cells must be well supplied with oxygen and feeding substances. And for this purpose any human being must have regular complete rest, i.e. sleep.

When the process of inhibition extends over a great number of cells, spreads widely over the cortex and even over the subcortical areas of the brain, one falls asleep.

When one sleeps the vital activity of the nervous system is restored. So, sleep is of a great protective significance to the human being.

The man sleeps about one third of his life. Numerous investigations and experiments have shown that sleep is more necessary for the human being than food. One can live longer without food than without sleep.

During a sound quiet sleep the whole activity of the human organism changes, the body metabolism decreases, the respiratory and pulse rates become slower, the body temperature drops. Though the stimuli continue to come into the brain, the inhibited cortical cells do not react to them.

CLASS ASSIGNMENTS

XIII. Choose the appropriate answer:

1. Why had the patient’s condition been complicated? (a) The patient’s condition has been complicated today because he feels pain in the heart area; (b) The patient’s condition had been complicated because he did not receive any treatment last month; (c) The patient’s condition will have been complicated if he does not receive any treatment by tomorrow. 2. What has been controlled? (a) The disease will have been controlled by the beginning of the next week; (b) The disease had been controlled before the patient was discharged from the hospital; (c) The disease has already been controlled and the patient is able to start his work again.

XIV. Read the pairs of sentences and answer the questions:

1. Patient Ivanov has already been operated on. Patient Smirnov must be operated on. Кого из них прооперировали?

2. The new book on the physiology respiration will have been published by the end of the year. The book The Anatomy of the Cardiac Blood Vessels by Prof. S. Samoilova has already been published in Moscow. Какая из книг будет издана?

XV. Translate the pairs of sentences. Define the infinitives:

The patient may be discharged soon. The patient may have been discharged by the 15th of the last month. 2. The process of inhibition in the cortex of experimental animals must be described in detail. The process of inhibition in the cortex of experimental animals must have been described after the observations.

XVI. Recall the usage of the word ‘one’. Translate the following sentences:

The brain is one of the most complicated mechanisms that has ever been constructed by nature. 2. In patients with tuberculosis the morning temperature is usually normal but the evening one is high. 3. In pneumonia one may observe considerable changes in the white blood cell count. 4. It is in infancy that one begins to develop first conditioned reflexes. 5. The right lung has three lobes and the left one only two.

XVII. Put the verbs given in brackets in the appropriate tense. Translate the sentences:

1. Important findings (to obtain) by the investigator before he finished his observations. 2. All the observations (to analyse) and (to summarize) by the physiologist by the end of his experimental work next month. 3. The patient (not to feed) since early morning because he will be operated on today.

XVIII. Supply participles instead of subordinate clauses:

The pleura is a special tissue which covers the lungs with a thin layer.