1) It is necessary to carry out an experiment that would test the hypothesis of two ways of regulation.
2) In order to prove the existence of nervous regulation, it is necessary to irritate the nerves that innervate that part of the gland that secretes digestive juice. If secretion increases, then nervous regulation exists.
3) In order to prove the existence of humoral regulation, it is necessary to stimulate the secretion of digestive juice by food, but in the absence of nervous regulation. To do this, you can cut certain nerves. And if, when food enters the duodenum, juice secretion increases, we can talk about humoral regulation.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.