He was admitted to McLean Hospital in April 1959, staying through May of the same year. There, he was diagnosed with paranoid schizophrenia . According to the Diagnostic and Statistical Manual of Mental Disorders , or DSM, a person suffering from the disorder is typically dominated by relatively stable, often paranoid, fixed beliefs that are either false, over-imaginative or unrealistic, and usually accompanied by experiences of seemingly real perception of something not actually present. Further signs are marked particularly by auditory and perceptional disturbances, a lack of motivation for life, and mild clinical depression .  
Thoreau ’s work develops many of the romantic themes towards nature. Especially in Walden , he is concerned with the degrading influence of too much society, commerce and industry and with the salutary effects of nature’s company. He was a frequent canoe traveler and mountaineer, and developed a daily habit of extensive hiking. Both Walden and his travel writings argue for the existence of deeper meanings and higher uses in nature than as mere material for the human economy. He found the aesthetic value of nature to be spiritually and morally important, and woefully underappreciated. But he also spoke of a broader point view, which sees the weeds as food for the birds and the squirrels as planters of the forest. Recognizing that nature, often in the very places it is widely despised, has hidden and indirect values, he anticipates the contemporary economic idea of ecosystem services.