Need help deciphering the meaning behind a phrase spoken in 1893

While trying to find a word that describes someone as having a fondness/interest in microbes, I stumbled across this Nature news article in 1893 that utilized the word, "bacillophil" seen below:

A WELL-KNOWN English writer a short time ago informed the public that
Prof. von Pettenkofer, the distinguished veteran in sanitary science
in Munich, expressed the opinion that "the atmospheric envelope of
this globe is at present in a bacillophil humour." Expressions such
as these have been repeatedly used in one form or another, some more,
some less witty; the intention being, of course, to convey an
exagerated impression of the frame of mind of over-zealous
enthusiasts. By such expressions more or less distinguished speakers
and writers have been enabled to exhibit the smartness of their
phraseology.

The issue I have is not being able to clearly understand the humor Pettenkofer expressed in the quoted sentence.

Could a linguist help me understand what the sentence mean in an 1893-context?

Thanks!

side note, it seems that there actually isn’t a definitive English word that describes someone as having a significant fondness in microbes–at least not in any dictionaries that I’ve looked through so far.

Reference:

Bacteria, their Nature and Function. Nature 48, 82–87 (1893). https://doi.org/10.1038/048082b0