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altering, to some extent at least, the end result of the chain. In other words, we shall hope to achieve thereby an amelioration of the symptoms.
We are thus led to a further question: "Which is the most important link in the chain of causes responsible for mental and nervous disorder?" There is no one answer to this question, because "mental and nervous disorder " includes a number of very different conditions, and the relative importance of the constituent links varies greatly as we pass from one to another. This will be made clear by a brief consideration of a few of the principal types of disorder which are encountered in our patients.
In one type the constitutional element is vastly the most important, and the condition of the patient is determined in the main by the original structure of his brain and nervous system. The chain here will be represented by the following figure, where the relative importance of the various links is indicated roughly by the size of the corresponding circle[1]:—
This is the type to which "mental deficiency" belongs. The patient has a cramped and undeveloped mind because he has been born with a
- ↑ In this and in the succeeding diagrams an unnamed circle has been inserted in order to indicate that the chain of causes shown is not complete, and that additional factors of all sorts and kinds play a part in determining that end result which we call the "symptoms."
