48 Compare the theories of spontaneous generation and biogenesis

he biogenesis theory claims that all living things arise from living things. This theory of biogenesis is completely opposite from the spontaneous generation theory. But before we go into the details of theory of biogenesis, let us understand the spontaneous theory of generation.

Spontaneous Theory of Generation

Long before 1900's, people believed that organisms could evolve from non living things. One of the early thinkers who believed that non-living things could spontaneously give rise to living things was Aristotle. For example, it was a common belief that logs gave rise to crocodiles, dirty sewers gave rise to rats, maggots came from dead bodies, wet soil lead to creation of toads, etc. This spontaneous theory of generation had a strong 'belief system' among people over many centuries.

Louis Pasteur and Theory of Biogenesis

Louis Pasteur was one of the most intelligent scientist of his time. He was the first to be able to prove this theory. He proposed that the organisms that are not visible to the naked eye are present in air. However, he emphasized on the fact that air did not give rise to living things. He carried out an experiment that would dissolve the spontaneous theory of generation and prove the theory of biogenesis.

In his experiment, Pasteur heated a number of short necked flasks that contained beef broth. After heating the flasks, he immediately sealed the mouths of some flasks and left a few unsealed. Then after a few days, microorganisms were observed in beef broth that was in flasks that were unsealed. The sealed flasks had no microorganisms present in the broth. This proved that the microorganisms were present in the air and could contaminate the beef broth without the seal.

Now, to prove that air did not give rise to organisms, he demonstrated another experiment. He filled long-necked flasks with beef broth and the flasks were bent into S-shaped curves. These flasks were heated to kill any presence of life in the beef broth. Then he left the flasks as they were for a few days without sealing them. This way the air could reach the broth as it was not blocked. After a few days, Pasteur observed the beef broth and found no microorganisms in it. This showed that the air can access the broth, but the organisms are trapped in the S-shaped neck of the flask and thus are not able to reach it.

This simple and ingenious experiment was enough to break an age-old theory of spontaneous generation. The world could now understand the relevancy and that only a living thing can give rise to a living thing. Thus, the mystical belief of non living things giving rise to living things was shattered by a simple experiment by Louis Pasteur. To summarize it, the theory states that all living things will be created only from living things and no other process

54 Calcve volumeulate your inspiratory reser

1Set up the spirometer. You will need either a new disposable mouthpiece to attach to the machine or you must clean the attached mouthpiece. Be sure that the spirometer is properly calibrated and has no leaks before using it to test lung volume. Read through and follow the specific directions for your machine.

2Explain the spirometer and the tests. Tell the person being tested how the spirometer works and what you will be testing. You can show him how it works by demonstrating with it or you can give a breathing lesson. Since the test can be affected by factors like nervousness, misuse or improper breathing, an explanation is necessary.

3Ask the person being tested to breathe normally for several minutes before testing. A spirometer can look intimidating or frightening, especially to someone who has never used one. Get the client calm and comfortable breathing before doing any specific tests.

4Test for tidal volume before inspiratory capacity. Explain the procedure first. The client will take a normal inhalation then exhale into the spirometer. The measurement will be this person's tidal volume.

5Explain how inspiratory capacity is tested. Tell your subject that she will need to breathe in deeply and fully, filling her lungs as much as possible. Then she will blow out the air inhaled into the spirometer for measurement. Explain that the exhalation into the machine is not forceful but complete. Then have the subject perform the actual inspiratory capacity test.

6Calculate inspiratory reserve (IRV = IC -- TV). To do so, take the measurement for inspiratory capacity (IC) and subtract the individual's tidal volume (TV) from this amount. The result is the individual's inspiratory reserve (IRV).