Curd and worms
I added a spoonful of curd to a cup of milk and left it for a week, after which some small white worms were noticed in the curd. How did the worms come into the curd vessel, which was kept closed?
B.V. Satyanarayana
Visakhapatnam, Andhra Pradesh
When we add the spoonful of curd to the milk, we aren't just adding curd — we are also adding hundreds of living things! This spoonful of curd is full of microorganisms that are too small for us to see with our naked eyes.
Major bacteria present in the curd are lactic acid bacteria (Lactobacillus sp.). They feed on the sugar (lactose) in milk, producing lactic acid as a byproduct.
As the bacteria reproduce using lactose as a source of carbon, it produces lactic acid as waste.
This lactic acid makes the milk taste sour. It also causes the milk proteins to become denatured and coagulated because of its acidic nature.
When this process is allowed for single day, we get a cup of curd. If it is prolonged for a week, the curd will get spoilt because of microorganisms.
Eggs of maggots are always present in the air if it is not filtered, so that when you had added the spoonful of curd to the milk, the eggs present in the air might have fallen in the milk.
The fly life cycle is composed of four stages: egg, larva (commonly known as a maggot), pupa, adult.
The eggs are laid in decaying flesh, animal dung, manure, or pools of stagnant water — whatever has ample food for the larva, generally in a moist area.
It can easily suspend in the air like fungal spores. After 8-20 hours, the egg hatches and the fly enters the maggot stage.
The maggot gorges itself on food until it is ready to enter the pupal stage, and adult worm develops.
That is why we find small white worms in the curd when kept for a long time.
The `original' experiment refuting `spontaneous generation' was done using common houseflies and maggots.
When raw meat at room temperature was covered with a cloth tent so that the flies could not land on the meat, no maggots hatched. The uncovered meat produced maggots because the flies were able to lay their eggs in the meat hence producing the maggots (Francesco Redi, 1668).
In 1768 Lazzaro Spallanzani proved that microbes came from the air, and could be killed by boiling.
Yet it was not until 1862 that Louis Pasteur performed a series of careful experiments, which conclusively proved that a truly sterile medium would remain sterile.
R. SEKAR
Department of Microbiology
Dr.ALM Post Graduate Institute of
Basic Medical Sciences
University of Madras, Chennai
Printer friendly
page
Send this article to Friends by
E-Mail
Sci Tech
