In Ch.9 Elizabeth out of concern for Jane's health requests Bingley to send for Mrs. Bennet so that she could decide whether Jane should be taken back to Longbourn or not; and soon "Mrs.Bennet accompanied by her two youngest girls, reached Netherfield soon after the family breakfast." Mrs.Bennet quickly realizes that Jane's condition is not serious and decides against her "being carried home." Bingley and Caroline Bingley assure her that Jane will be taken good care of while at Netherfield.
Although Bingley is genuinely concerned and sincerely wishes that Jane stay at Netherfield, his sister merely pretends to be concerned. This is evident from the expression, "cold civility" to describe Caroline's assurances to Mrs.Bennet that Jane will be taken good care of while at Netherfield.
Mrs.Bennet embarrasses and annoys both Darcy and Bingley by foolishly insisting that the English countryside has more attractions to offer than London city itself!
"I assure you there is quite as much of that going on in the country as in town."
The reaction of all the others is one of shock and surprise:
" Everybody was surprised and Darcy after looking at her for a moment, turned silently away."
Darcy snubs Mrs.Bennet by refusing to respond to her silly remark. But this only forces her to be rude to Darcy by making a pointed reference to him:
"But that gentleman," looking at Darcy, "seemed to think the country was nothing at all."
Caroline Bingley meanwhile looks suggestively and smiles knowingly to Darcy, hinting that if he were to marry Elizabeth he'd have to care for a foolish mother in law like Mrs.Bennet!
To make matters worse, Mrs.Bennet reveals that Jane when she was only fifteen years old was courted by a man, but that nothing much came out of it. Darcy on hearing this "only smiled."
Finally, Lydia the youngest and most spirited girl virtually pesters Bingley to agree to give a ball at Netherfield. Bingley sportingly agrees saying that once Jane has recovered he will give the ball.
Darcy who has been silently observing Mrs.Bennet's and Lydia's behaviour has quietly formed a very poor impression of them both and is convinced that it would not be wise for his friend Bingley to marry into such an ill mannered family. However, his attraction for Elizabeth has not undergone any change. This is evident in last line of Ch.9 where he refuses "to join in their censure of her [Elizabeth] in spit of all Miss Bingley's witticisms on fine eyes."