In 1951 J.D. Salinger published his book The Catcher in the Rye, a book about the value of innocence and protecting it. In this book Holden Caulfield, the book's main character, shows many symptoms of various mental illnesses, mainly depression. Symptoms of depression are anxiety, loss of interest, insomnia, sadness, excessive crying and lack of concentration. Holden shows most of these symptoms.
Holden has many reasons to feel depressed, he is constantly being kicked out of schools and people around him have a tendency to drop dead. At one of his schools his classmate, James Castle, was confronted and promptly jumped out of a window as a result. Holden, who was showering at the time heard the thud and goes to investigate. When he arrives at the scene he is met with the unsightly body that was James Castle, his teeth and blood everywhere in Holden's sweatshirt. This comes after his brother, Allie, died of tuberculosis.
Holden shows many symptoms of depression a few being excessive crying, as seen in his interactions with the prostitute he ordered. His loss of interest shown by his constant expulsions from various schools. His anxiety that more people he knows will die with him around and insomnia. Based on this information I would say he suffers from depression as he lands himself in a mental hospital at the end of the book.
In conclusion Holden suffers from depression caused by the deaths of both Allie and James Castle that happened around him. The signs he shows are insomnia, anxiety, loss of interest, and excessive crying. All of these point to Holden suffering depression.