Answer: One of two reasons: Either they are found to be dead ends and are abandoned, or (and this is more likely): They are proven to the scientists satisfaction - which immediately, as any scientist will tell you, begs three more new questions. In the scientific method, answering a question always leads to new questions, which eventually become theories to prove or disprove.
Answer: A lot of information is pretty specific to a particular aim being rationalized in the paper. Hence, it does represent a very esoteric viewpoint that may not hold true for all systems in general. Right now, there are many papers which seem to portray "good" information through experiments in the not the "best in-vitro setups". The best information can be obtained via clinical trials only. If you see in-vitro or mouse models, you can be rest assured that although the methodolgy works, there is a very long way to go before one can optimize the system for clinical trials. another name for thigh bone is femur
Answer: In ballet it would be called "standing on the ball of the foot." this is all the toes and the pad of the foot still in contact with the floor.However if you were to stand right on the end of your toes, this is with only the ends of your toes suporting your weight this would be called "en pointe" (on point) of course you are not advised to do this unless you have the correct training and special shoes.