Who Studied bacteria & how blood flowed through blood vessels?

Immigrants arriving in the united states during the late 1800s experienced many difficulties. which of the following was a problem which large numbers of immigrants faced?

Black death spread because of what problem in medieval europe? which one is it i need the answer quick . a- overcrowded cities b-too many farm animals c-not enough qualified doctors d-all of the above

Social darwinism applies what theory to human society