to permit oneself to be subjected to something

"Docile" is often used to talk about animals, but it can be said of humans too. "Submissive" is not said of animals, only people.In many, if not most, situations, you could probably use either word, but there are some nuances to think about to really get at what you are trying to say. I think of "docile" as being more passive than "submissive". When someone is docile, they are simply compliant, while submissive implies to me that they are actively choosing to obey or comply. "Docile" is a state of being, while "submissive" is a behavioral action or behavioral tendency; one can submit against one's better judgment, but to be docile implies that you don't even have such a judgment and just go along with whatever. Or maybe, "submissive" implies that one has an independent will that one is submitting to someone else's will, such as an authority figure, while "docile" implies that no such will exists.

@ John - Excellent explanation! :)

As far as I can tell, John`s answer  is good. Docile suggests more a character trait and submissive suggests more moment-specfic behaviors. It can be used with animals or people. A guard dog might be willing to tear the arm off an intruder, but at the same time be totally submissive to it´s owners. A kitten is a rather docile animal by contrast all the time. 

Docile means controlled

E. G. (His student were docile and eager to learn)

Submissive means obey some one

E. G ( submissive person)