By the courtesy of Sir Patrick Manson, K.C.M.G., I am permitted to show you specimens of (1) the trypanosoma from the human subject, an European, which is the first instance of such a discovery; (2) in monkey got by injecting human trypanosomes, the specimen being one, I believe, of Dr. Castellani's own preparation; and (3) the Tryp. Lewisi from the sewer rat. I make no apology for drawing attention to the possible cause of a disease—sleeping sickness—which is so nearly allied in its clinical symptoms to the condition of katatonia or hebephrenia, two of the varieties of dementia præcox which, in increasing numbers, many of us are called upon to treat. Recently my colleagues and myself have made an unsuccessful attempt at lumbar puncture in order to have examined the cerebro-spinal fluid of a case of katatonia. Let us briefly contrast the trypanosoma with the malaria parasite.