The type of sampling where the individual himself introduces the other subjects of surgery is called as:

Snowball sampling is a technique for developing a research sample, where existing study subjects recruit future subjects from among their acquaintances. It is a type of non-probability sampling. This sampling technique is often used in hidden populations which are difficult for researchers to access; example, drug users or commercial sex workers. Thus, the sample group appears to grow like a rolling snowball. Because sample members are not selected from a sampling frame, snowball samples are subjected to numerous biases.