Reference for Yoma 167:10
לא למעוטי מקיזין דם לסרונכי ה"נ מסתברא דתניא שלשה דברים א"ר ישמעאל בר' יוסי ששמע משום רבי מתיא בן חרש מקיזין דם לסרונכי בשבת ומי שנשכו כלב שוטה מאכילין אותו מחצר כבד שלו והחושש בפיו מטילין לו סם בשבת
What is its symptom? - If he puts anything between his teeth, his gums will bleed. When R'Johanan suffered from scurvy, he applied this [remedy] on the Sabbath and was healed. How could R'Johanan do that?<span class="x" onmousemove="('comment',' Since that does not seem to be a dangerous disease, justifying the application of medicine on the Sabbath day. By Rabbinic ordinance that is forbidden, as a fence around the law (Aboth I, 1) to prevent its leading to the grinding of spices for medicinal purposes, grinding being one of the thirty-nine kinds of labour prohibited by Biblical law on the Sabbath.');"><sup>10</sup></span> - R'Nahman B'Isaac said: It is different with scurvy, because whereas it starts in the mouth, it ends in the intestines.