In the early days of germ theory, contagious diseases were thought to be caused only by fungi or bacteria. In the 1890s, Dmitri Ivanovski filtered extracts from diseased tobacco plants and discovered that the disease could be transmitted to new plants through the filtrate. He hypothesized that something smaller than bacteria or fungi was responsible for the transmission of the disease. Which best explains how Ivanovski's work led to a change in the germ theory? He tried to promote his hypothesis as a law. He used a new experimental method to test his hypothesis. He used a more powerful bacterial strain than other scientists had. He obtained results that confirmed what other scientists were thinking.

Dmitri Ivanovski, a Russian microbiologist who was born in the year 1864 and died in 1920. He was the scientist who initiated the discovery of viruses as a pathogenic microorganism. He worked to discover the cause of mosaic disease in tobacco plant and he hypothesized that that something smaller than bacteria or fungi, as early believed, was responsible for the transmission of the disease.

In order to test his hypothesis, he passed a solution containing the causative agent of the disease, which he prepared from the infected plant leaves, through a filter known as Chamberland filter. He was able to discover that the filtrate still contained microbial pathogens that can infect more tobacco plants, confirming his hypothesis that something smaller than fungi or bacteria is responsible for the tobacco mosaic infection.

Hence, to test out his hypothesis, Ivanovski in the 1890's used a new experimental method i.e. CHAMBERLAND FILTER method.