Poisoned by Oxygen
There was a good reason for the scientists’ interest in oxygen poisoning. The problem was how to facilitate the work of divers. A man can survive in an atmosphere of pure oxygen for about twenty-four hours. If he breathes oxygen for longer than that, pneumonia ensues and, strange as it may seem, death due to asphyxia, which is a shortage of oxygen in the most important organs and tissues. A man can endure a pressure of two to three atmospheres not longer than one and a half to two hours. Then he becomes intoxicated with oxygen, loses coordination of movement, and suffers from mental distraction and loss of memory. If the oxygen pressure exceeds three atmospheres, convulsions will soon follow causing death.
Oxygen proves even more poisonous for animals which live where there is a critical lack of oxygen. This is how ascarides living in human intestines are combated. Oxygen is fed into the intestines, causing no danger to the man himself, but surely killing the parasites.
An excess of oxygen is not only detrimental to animals, but also to plants. It is interesting that, although plants saturate the atmosphere of our planet with oxygen, the Earth’s atmosphere is not good for them. They are rather short of carbon dioxide and, strange as it may seem, there is too much oxygen for them. According to recent investigations not only the usual concentration of oxygen but even as little as two per cent, that is one-tenth of what is to be found in the atmosphere, considerably retards photosynthesis. This means that plants have created an atmosphere quite unsuitable for themselves. Had there been less oxygen they would have grown and developed more rapidly.
Filed under oxygen | Tags: breathing, carbon dioxide, excess of oxygen, lack of oxygen, oxygen, oxygen poisoning, oxygen shortage | Comment (0)Combatting Oxygen Shortages
Animal kingdom emerged on our planet when the atmosphere was still very poor in oxygen. It is no wonder that living organisms had to adapt themselves to an environment where oxygen was in short supply. However, we usually fail to notice another much more puzzling phenomenon, namely, that animals living in the presence of excessive oxygen have managed to restrain the intensity of the oxidation processes taking place in their bodies as if they were always ready to extinguish a constantly threatening fire.
The amount of environmental oxygen is constant, and, if it does alter, it decreases. This explains why animals have different means of combatting oxygen shortages, but no means of protection against excess oxygen.
Paul Bert was the first to discover that breathing pure oxygen can be poisonous around a hundred years ago. This was such an unexpected discovery that scientists did not believe him and a suspicion arose that the oxygen used by Bert contained various poisonous admixtures. The experiments were repeated many times, but no matter how thoroughly the oxygen was purified, the animals which breathed it for prolonged periods inevitably perished.
Filed under oxygen | Tags: animals, breathing, oxidation, oxygen, oxygen shortage | Comment (0)Oxygen, Energy and Wastefulness
The question arises why living organisms use atmospheric oxygen if energy can be obtained by mere fermentation. There are many important reasons for this. Fermentation never results in the complete oxidation of a substance and, therefore, little energy is released. If one gram-molecule of glucose is completely oxidized to carbon dioxide and water, 673 large calories will be obtained. But with fermentation, which results in the formation of ethyl alcohol and carbon dioxide, only as little as 25 large calories will be released, i. e. almost 27 times less. This means that anaerobes have to use 27 times as much glucose as aerobes to obtain the same amount of energy. The difference is, of course, appreciable and nature cannot tolerate such wastefulness.
Another important reason is that substances such as ethyl and butyl alcohol, lactic and butyric acid, acetone, etc., which are bad for the organism, are formed as a result of fermentation. It is not easy to dispose of these harmful substances.
Respiration frequently produces combustible gases. Microorganisms often release hydrogen. This is how microbes living in the intestine of termites breathe. Of the multicellular creatures, the larvae of some flies, in particular, release a great deal of hydrogen. Some organisms liberate not only hydrogen, but also methane and other gases, some of which are still not known, including spontaneously inflammable gases. It is a particularly beautiful sight when the gases, which have collected in the silt at the bottom of a pool, rise to the surface of the water and burn with a mysterious bluish flame.
How then have animals managed to change their way of breathing to such an extent and adapt themselves to an absence of oxygen? This did not prove difficult. At the dawn of life on the Earth there was little free oxygen and the earliest living creatures had to become anaerobes. It was not until the atmosphere became rich in oxygen that animals learned to burn energy-forming products completely. At the same time, the anaerobic method of breathing did not disappear but was passed on and finally came down to us.
As has been mentioned at the beginning, in all animals without exception the first stages of energy release proceed without oxygen. When aerobic animals felt like returning to the places where no oxygen could be obtained, they again had to restrict themselves to partial utilization of the energy contained in nutrient substances. To do this they had to remember how to render partially oxidized products harmless.
Filed under oxygen | Tags: aerobes, anaerobes, breathing, carbon dioxide, hydrogen, oxidation, oxygen | Comment (1)How Anaerobes Breathe
Still more primitive animals, primarily bacteria, have no haemoglobin and are therefore unable to actively extract oxygen from their surroundings. However, they are often doomed to environments where there is little or no oxygen at all. Nevertheless, these creatures are quite happy to reconcile themselves to an absence of oxygen. This led to their being named anaerobes, which means ‘one who lives without air’.
How do anaerobes manage to live without air? Not so long ago this has seemed to be a puzzle that could not be solved. Now we know that they do need oxygen all the same. Instead of extracting oxygen from the atmosphere the anaerobes simply take it from organic substances. Some bacteria even extract oxygen from inorganic substances, using nitrites and sulphites for the purpose.
Anaerobes breathe by oxidizing the products of metabolism without using additional oxygen and are quite content with the amount already present in the substance being oxidized. For, when a substance is oxidized, it makes no difference whatsoever whether oxygen is added to, or hydrogen removed from it.
Filed under oxygen | Tags: anaerobes, bacteria, breathing, extract oxygen, haemoglobin, oxygen | Comment (0)Striving For a Breath
Tiny oxygen bubbles can often be observed on plants. The macroplea, beetles pick up these bubbles with their tiny legs and carry them to their antennae. After some time, the bubble disappears which makes us think that the beetles breathe with their antennae. If there are no gas bubbles of oxygen, the beetles cut the plant and wait for air to escape from its air channels. The same method is used by water weevils.
The larvae of macroplea and donicia beetles make incisions in plants and attach their spiracles to them. Other insects stick their stylets into the plants and suck oxygen out from the intercellular space. These oxygen-rich intercellular spaces are places favoured for pupation.
However, the caterpillars of the Brazilian paraponyx are even more ingenious. They build themselves a house from bits of green plants and, when these wither away, replace them. Consequently, during the hours of daylight, there is always plenty of oxygen in their nests, but at night, so as not to be choked by the carbon dioxide liberated by the plants, the caterpillars have to climb outside.
The amount of oxygen found in the stomachs and intestine of vertebrates is negligible. But certain living organisms which could find no place under the sun learned how to obtain oxygen. Not the least among them is the bot (the larva of the botfly) which lives in the alimentary tract of horses. Like all other insects, the bot has a tracheal system for respiration which is stronger and more ramified than that of larva living in the open. It also has red organs which are a conjugate formation consisting of many large red cells. A tracheal stem enters each cell and then branches out into numerous tracheoles in its protoplasm.
Filed under oxygen | Tags: breathing, carbon dioxide, intercellular, oxygen, plants | Comment (0)Shortage of Oxygen
Our atmosphere contains a great deal of oxygen and its loss is constantly made good by green plants. It seemed that man would never have to face a shortage of oxygen. However, it must be acknowledged with great distress that this hope is fading.
A few years ago the Japanese were forced to make reserves of oxygen available in ordinary, everyday conditions. The streets of Tokyo and other large cities in Japan are always packed with cars whose fumes poison the air with carbon dioxide and carbon monoxide. Such air is unsuitable for breathing, although it still contains sufficient oxygen.
The traffic wardens who are working for many hours in the streets are unable to last out a whole shift. To avoid excessive poisoning, they have to be supplied with oxygen. It is now a long-standing practice to provide police stations with cylinders of compressed air so that the policemen can take a breath of good air from time to time. Now they have started to install oxygen machines in the streets of Tokyo for passers-by, too, similar to the aerated water machines that are to be found in many cities the world over. This means that everybody can put a coin in the machine and refresh his lungs with oxygen.
Filed under oxygen | Tags: atmosphere, breathing, carbon dioxide, lungs, oxygen | Comments (2)Haemoglobin & Reserves of Oxygen
Our planet is very rich in oxygen, and this evidently explains why animals did not learn to store it in large amounts. Only very few Earth-dwellers are able to provide themselves with large reserves of oxygen, although many frequently stock it in small amounts.
Although it takes the blood only two seconds to pass through the capillaries of the alveoli, this is sufficient for an oxygen balance to be set up between the air in the alveoli and the blood. However, the amount of oxygen which can dissolve in the blood during this period is infinitesimal (0.003 cubic centimetre per cubic centimetre of blood plasma). For an animal to obtain sufficient oxygen using this method the volume of the lungs and the amount of blood running through them would have to be increased almost a hundredfold. This would obviously be very difficult to do.
Nature has chosen another method, by supplying the blood with a substance which can easily react with oxygen and thus retain it in much larger amounts than would be possible in a simple solution. For the tissues to be able to make use of the stored oxygen this substance must readily release the oxygen when necessary. This substance is haemoglobin. It possesses two properties which are indispensable for breathing. When the blood is in the lungs, where there is a great deal of oxygen, the haemoglobin immediately makes contact with the oxygen. Owing to this, one cubic centimetre of blood carries with it 0.2 cubic centimetre of oxygen, i. e. 20 per cent of the blood volume, and then gives it up to the body tissues.
Filed under oxygen | Tags: alveoli, blood, breathing, haemoglobin, lungs, oxygen | Comments (3)