Biological problem 2 How plasmodium gets into the blood of man?
Observation
Biologists were having following observation".
- Malaria is associated with marshes
- Drinking water of marshes does not cause malaria
From these observation it can be concluded that plasmodium was not in the marsh water. But it must be carried by something that comes to marsh water.
In 1883,a physician A.F.A. King listed twenty observations. Some important observations ofA.F.A. King were:
- People who slept outdoors were more likely to get malaria than those who slept indoors;
- People who slept under fine nets were less likely to get malaria than those who did not use such nets'and
- Individuals who slept near a smokey fire usually did not get malaria.
Hypothesis
On the basis of these observations king suggested a hypothesis:
"Mosquitoes transmit plasmodium and so are involved in the spread of malaria"
Deductions
Following deductions were made considering the hypothesis as true:
"If mosquitoes are involved in the spread of malaria than,plasmodium should be present in mosquitoes."
"A mosquito can get plasmodium by biting a malaria patient"
Experimentation
In order to test the above deductions ronald ross, a british army physician working in india in 1880's, performed important experiments.
He allowed a female anopheles mosquito to bite a malarial patient.HE killed the mosquito some days later and found plasmodium multiplying mosquito's stomach.
The next logical experiment was to allow an infected mosquito (having plasmodium) to bite a healthy person.If the hypothesis was true, the healthy person would have got malaria,but scientists avoid using human beings for experiments when the results can be so serious.
Ross used sparrows and redesigned his experiments. He allowed a female Culex mosquito to bite on the sparrows suffering from malaria.Some of the mosquito were killd and studied at various times. Ross found that plasmodium multiplied in the wall of the mosquito's stomach and then moved into the mosquito's salivary glands.He kept some mosquitoes alive blood of mammals or birds for the maturation of their eggs. Ross found that the saliva of the infected mosquito contained plasmodium and these entered the sparrow's blood. When he examined the blood of these previously healthy sparrows, he found many plasmodium in it
In the end, the hypothasis was tested by direct experimentation on human beings. In 1898 italian biologists allowed an Anopheles mosquito to bite a malarial patient.The mosquito was kept for a few days and then it was allowed to bite a healthy man. This person later became ill with malaria.In this way, it was confirmed that mosquitoes transmit plasmodium and spread malaria.
Transmission of plasmodium
When a female mosquito pierces the skin with her mouthparts,she injects a small amount of saliva into the wound before drawing blood.The saliva prevents the blood from clotting in her food canal.
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