What did Mr. Ages say Timothy had?
In the second chapter of Robert O'Brien's Mrs. Frisby and the Rats of NIMH, the title character Mrs. Frisby ventures out to see a white mouse whom she knows named Mr. Ages; she hopes Mr. Ages can help with Timothy's illness because he knows a great deal about making "draughts and powders that could sometimes save the sick from dying."
Mr. Ages asks her questions about Timothy's symptoms, and Mrs. Frisby relays that his fever is so high he is delirious, perspiring, and shivering. Also, his tongue looks purple; his pulse is so fast you "cannot tell one heartbeat from the next"; and, he is breathing rapidly but has no cough.
Based on those symptoms, Mr. Ages determines Timothy has pneumonia and gives her some medication to give to him. He gives her three packages of medication and directions for administering the doses. However, he warns that Timothy will be in danger of getting the pneumonia again, even worse than now, should he breath in any cold air; he will be unstable and in danger for about a month.