* Early Observations: While bacterial capsules were likely observed by early microscopists, they couldn't be definitively identified or understood due to the limitations of technology.

* Gradual Understanding: The concept of a capsule surrounding bacteria developed gradually through the 19th and 20th centuries.

* Key Discoveries:

* 1880s: Louis Pasteur and others observed "haloes" around bacteria, suggesting a surrounding layer.

* 1902: Richard Pfeiffer described a "capsule" around _Haemophilus influenzae_, but its composition remained unclear.

* 1930s: Techniques like capsule staining and electron microscopy provided more detailed observations and evidence of the capsule's existence.

* 1940s-1950s: The chemical nature of capsules started to be understood, revealing their polysaccharide composition in many cases.

Therefore, instead of a single date, the understanding of bacterial capsules arose through a series of observations and advancements in microscopy and biochemical techniques.