The Rosh certainly holds that we rely on doctors, for his entire primary difficulty is based on this reason. It also seems to me that the Sugya of the Gemara can be settled according to his words: that Rabbi Yitzchak bar Chanina did not ask about dry blood when she saw it, for in that case it certainly requires being dissolved, and therefore he did not say "one who sees dry blood, what is the law?" Rather, this is the explanation: that he asks regarding the Mishnah of "one who discharges a piece," if there is blood with it she is impure, and similarly in "one who discharges something like fish," see there, what is the law if the blood was found dry? And he did not inquire whether it requires being dissolved, for it certainly requires it; rather, on the contrary, perhaps even when dissolved she is pure, and it is not similar to "one who discharges shells and hairs" where if it is dissolved she is impure, for perhaps they themselves are not complete blood but inside them is complete liquid blood. And he resolves it for him from the Mishnah of "the blood of the Niddah," and one cannot say that from there there is no proof since it was previously liquid, and he resolves it for him from "one who discharges shells etc." for it is difficult: from where do we know that previously there was liquid inside them? Rather, it is certain that even that which is dry, when it is dissolved, she is impure. And it asks: "If so, even when it is not dissolved as well," meaning, according to your words that even that which was dry from its inception, when dissolved, is impure, if so, why do I need to place it in water so that it shall be dissolved? Even if it is not dissolved as well, for regarding that which was liquid and became dry, there is more reason for it to be called blood, as it says previously. And since even in that which was dry from its inception it is called blood when dissolved, if so, even if it is not dissolved as well it should have been called blood; for how is it possible that at the time of its exit it does not need to be liquid, which is then the primary seeing, and afterwards we should require it to be liquid? For it seems more logical to require it to be complete blood at the time of its exit than afterwards. And it answers that when it is not dissolved it is a distinct entity; meaning, that which we require it to be dissolved is in order to know if it is a type of blood at all, and had we known that it is a type of blood, we would not require it to be dissolved. And so too with all dry blood, when it cannot be smeared, we say that this is not a type of blood at all, as the Rosh wrote there. And regarding this it asks: "And is there such a case etc."
והרא"ש וודאי ס"ל דסמכינן ארופאים שהרי כל עיקר קושיתו מטעם זה וגם סוגית הש"ס נ"ל ליישב לדבריו דריב"ח לא שאל על דם יבש כשראתה, דבהא וודאי צריך נמוחו ולכן לא אמר הרואה דם יבש מהו אלא דה"פ ששואל על משנה דהמפלת חתיכה אם יש עמה דם טמאה וכן במפלת כמין דגים ע"ש איך הדין אם נמצא הדם יבש ולא איבעי ליה אי צריך נמוחו דוודאי צריך אלא אדרבא דאולי גם בנמוחו טהורה ולא דמי למפלת קליפות ושערות דנמוחו טמאה דשמא הם עצמם אינם דם גמור ובתוכם דם גמור לח ופשיט ליה ממשנה דדם הנדה וא"ל דמשם.אין ראיה כיון שהיה מקודם לח ופשיט ליה מהמפלת קליפות וכו' דקשה מנלן דמקודם היה בתוכן לח אלא וודאי דאפילו יבש בשנמוח טמאה ופריך אי הכי כי לא נמוח נמי כלומר לדבריך דגם יבש מעיקרו כי נמוח טמאה א"כ למה לי להטילו למים כדי שהא נמוח אפילו לא נמוח נמי דהא לח ונעשה יבש יש יותר סברא להקרא דם כמו שאומר מקודם וכיון דגם ביבש מעיקרו מקרי דם כי נמוח א"כ אפילו אם לא נמוח נמי היה לו להקרא דם דאיך אפשר דבשעת יציאתו א"צ להיות לח שאז הוא עיקר הראייה ואח"כ נצריכו שיהיה לח דיותר נראה להצריכו שיהא דם גמור בשעת יציאתו מאח"כ ומתרץ דכשלא נמוח הוה בריה בפ"ע כלומר דהא דמצ רכינן נמוח זהו כדי לידע אם הוא מין דם כלל ואלמלי היינו יודעים שהוא מין דם לא היינו מצריכים שיהא נמוח וכן בכל דם יבש כשאינו נמרח אמרינן שאין זה מין דם כלל כמ"ש הרא"ש שם ולזה פריך ומי איכא כה"ג וכו':