Sentence:  Serum potassium at this time was 3.8 mEq. per liter , and the hemoglobin was 13.9 gm. By <WSD>Dec.</WSD> 1 , 1958 , the weakness in the pelvic and quadriceps muscle groups was appreciably worse , and it became difficult for the patient to rise unaided from a sitting or reclining position . 
Meaning of the word marked with <WSD> tags:  the last (12th) month of the year