The science of life : fully illustrated in tone and line and including many diagrams

BOOK 1

solutions in the plasma that the great majority of transported substances are carried by the blood.

It will be interesting to survey this curious miscellany of plasma-ingredients very briefly, because by so doing one gains an insight into the number and variety of the functions performed by this essential fluid.

In the first place blood fetches and carries for all other tissues. It brings them supplies of oxygen and of various kinds of food they require, and it takes away and eliminates various unwanted products of their activity. The red cells are solely responsible for the transport of oxygen and they play the chief part in carrying carbon dioxide ; the remaining duties are undertaken by the plasma. Dissolved in the plasma are all the many and complex food supplies that cells need, and the waste products are simply shed by the cells into it. These two duties alone necessitate the carrying of a great number of different compounds—some in considerable amount, others only in minute traces.

But besides the bringing and taking away of substances which participate directly in the chemical processes of the cell-machines the plasma carries other matters, not actually consumed by cells, but necessary constituents nevertheless of the fluid which bathes them. A cell needs not only fuel and oxygen to work, but its delicate mechanism is acutely susceptible to the presence or absence of certain mineral salts in the surrounding fluid. Its activities respond to the slightest changes in their proportions. A minute trace of calcium must, for example, be present if our muscle-cells are to obey our will. Withdraw that and they will begin a rhythmic twitching. There is a whole range of such accessory substances in the blood needed for the proper working of the body.

Here, then, we have the primary functions of the blood, fetching and carrying for the tissue cells, for multifarious citizens of our body, and ensuring them the comfort necessary to their activity. These functions alone mean a very great complexity. But superimposed upon them are others, still more intricate and extraordinary. Day by day, and as a general rule quite outside the realm of our consciousness, there is a continual fight against certain evil forces that seek perpetually to disturb our serenity. Generally this conflict troubles us as little as the criminal activities of Pimlico and Shoreditch disturb the mental peace of the Prime Minister in Downing Street. But sometimes the criminal onslaught gets sufficiently out of hand to disturb the central

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THE SCIENCE OF LIFE

CUEVASR TER:

to

government. Swarming in the air we breathe, lurking on the solid objects we touch, and even on the surface of our own skin, are the spores of minute bacteria, many of them ruthless parasites, waiting for a chance to work us mischief. Constantly, through a scratch in our skin, through the tender lining of our lungs, through the injured tissues of a sore throat, swarms of bacteria invade the blood-stream

‘itself, and finding themselves in a medium

specially adapted for bathing and nourishing living cells, they rejoice and multiply exceedingly. ‘The very efficiency with which blood performs its normal ministering function makes it the most attractive and stimulating environment for these parasites. Many of them are extremely troublesome and ungracious guests. They produce their own often very disagreeable by-products, and make mischievous changes in the composition of the blood. They invade and attack the tissues. Unless they are defeated and repelled they produce the colds, influenzas, fevers, epidemic diseases, typhoid, small-pox, and so forth that disturb and may overthrow the central government altogether. The resistance, once skin or membrane is pierced, goes on almost wholly in the blood.

The chief antagonists of the bacteria themselves are the white blood corpuscles. These actually fight the bacteria. That war goes on interminably. It is only in the more serious engagements that painful congestions and inflammations make Mr. Everyman aware of the mischief afoot. In addition, in a manner too complex to explain at this stage, the chemical poisons which the invaders pour into the plasma are neutralized by specially manufactured antidotes. These chemical invaders, these poisons and antidotes, formed only in minute traces but nevertheless physiologically potent, constitute another class of ingredients in that complex fluid, the plasma, and provide another type of event in the swarming highways of the living cell-community which we call a man.

The composition of blood is further complicated by a second kind of protective arrangement—not in this case against living invaders, but against a more direct result of mechanical injury to the animal body. This is the provision for forming clots. When the surface of the body is cut or scratched and the injury involves bloodvessels, the escaping blood, as we know, clots into a solid mass and so seals the wound. Were it not for this fact, there would be nothing to prevent blood flowing away