To solve this puzzle you will have to get all the red vials to the left and the blue to the right. When you release a vial, the weight will cause each lever below to fall down depending on which side the opening is on. If the lever is up-right, it will fall down-left. If it is up-left, it will go down-right. The first section is easy, just plan out in your head which way each will fall and put the correct vial in.

During the second phase, the vials will sometimes get stuck as the lever will now require the weight of two vials to fall. When this happens, ignore that vial for now and continue to do the same thing you did during the first section. You will have to put an opposite vial in to the other side so it gets injected, then come back and put another vial of the same color down on top of the stuck one so it can then fall and two will get injected at once.

~Int