While the rich of the latter half of the 19th century could afford wet nurses, the doctors strongly encouraged ladies to breast feed their own children. However, the growing middle class & poor needed other ways to feed babies. They had to work.
Fortunately, the invention of vulcanized rubber provided a soft and flexible artificial teat that could withstand the heat of sterilization.
Various shaped glass bottles were created, all with a narrow glass mouth filled with a stopper. A length of Indian rubber tubing was inserted into the stopper, it's other end fitted with a bone mouth shield and a rubber teat.
You could buy them at your local chemist, who put them together as he thought best, resulting in a great variety of shapes and designs. However, there was one consistency among the bottles. All were impossible to keep clean and a serious health risk to babies.
The medical profession openly condemned the use of them, but this general design continued to sell well into the 1920's. For the first time, the baby could be left unattended to feed, freeing up the hardworking mother to do other tasks.
Infant mortality remained very high, with nearly 20% dying in their first year. Don't marry that percentage, because the stats of mortality in the 19th century are highly contested by today's statisticians. But everyone agrees they were high.
However, I can say sanitary conditions were dismal, bacterial infections a major cause of death and antibiotics had yet to be discovered. Mothers were strongly advised to breastfeed their own children, preferable to hiring a wet nurse, and strongly preferable to feeding with a baby bottle.
A change in baby bottle design occurred in 1894, claiming to be easier to clean.
Note the right end of the bottle is an open mouth. That's so you can pour in the milk. A metal cap fitted over it once it was filled. I expect it leaked but this model claimed to be far more sanitary than the prior bottles and it quickly became a best seller.
Now all you had to worry about was the milk you put inside it. Yes, that was a problem as well. The milk sold back then was often tainted.
End result: The doctors were absolutely correct. Bottle feeding added serious risks to your baby's health.
In book 5 of the X & V books, Vic rescues a baby who is drinking from a bottle of sour milk. She convinces the uncaring mother to give up the child and let her find it a good home. Vic gives it to her sister along with a healthy wet nurse.