第41次打卡（12月23日）

Let's have a quick look at ......history.The discovery ......to ......boost body immune system by making it insensitive to particular disease called bacterial was made by 19 century English doctor called ......He noticed the survive of small ......a common but extremely dangerous disease never contracted the disease a second time.In other words,they were immune.He studied the similar disease ......called ......and realized ......contracting with the infected...... became ill with......resembling small ......However,this was quite mile by comparison and those who cobtracts ......immune to small......He conducted next experiment by injecting child with a small amount of ......taken from the cow......The child subsequently became ill but soon recovered.Later,he injected the child with ......and the child didn't get sick.He developed ......to the more dangerous diseases.The anti body produced ......had been able to find small......bacterial.