1) PERMISSION FOR A DOCTOR TO HEAL
QUESTION: The Gemara derives from the extra phrase of "Rapo Yerapei" (Shemos 21:19) that a doctor is permitted to heal sick people.
Why would one have thought that a doctor is not permitted to heal a sick person, had the Torah not included the extra word "Yerapei"? The verse refers to a situation in which one person causes bodily damage to another, and the victim needs to pay a doctor to heal him. It is obvious from the verse, even without the extra word, that a person who is harmed does not have to passively accept the fate of being wounded by the other person, but that he may go to a doctor to be healed.
ANSWERS:
(a) RASHI and TOSFOS seem to understand that the Gemara learns from the extra word that even when a person becomes sick or bruised without human intervention, but rather as a Divine decree, a doctor still is permitted to heal him. One might have thought that this is a matter of faith in Hash-m and that a person should trust that just as Hash-m brought the illness upon him, Hash-m will take it away. The verse teaches that it is not considered a lack of faith to turn to a doctor for healing (as long as he recognizes that it is ultimately Hash-m who enables the doctor to heal him; TESHUVOS HA'RASHBA 1:413).
The RAMBAN (Vayikra 26:11) indeed writes that a person with a high level of trust in Hash-m will not turn to a doctor but will ask Hash-m to heal him directly. (See Insights to Berachos 60:2.)
The Rashba adds that this verse teaches that one is even permitted to use methods that are poorly understood and apparently superstitious in order to heal the sick, as long as they have been proven to be effective. As Abaye and Rava teach in Shabbos (67a; see Insights there), anything done in order to heal is not a transgression of "Darchei Emori" (following the idolatrous ways of the Emorites). Accordingly, the verse teaches that healing in such a manner does not resemble idolatry in any way. (See Insights to Berachos 10:2, where we explain that this might have been the reason why the Chachamim praised Chizkiyah for hiding the Sefer Refu'os.)
(b) The MOSHAV ZEKENIM (Shemos 21:19) explains that this Derashah is similar to the Derashah of "Shale'ach Teshalach" (Devarim 22:7; see Bava Metzia 31a and Chulin 141a), which teaches that one must send away the mother bird "even 100 times." Here, too, the verse teaches that a doctor may attempt to heal many times if previous efforts failed. One might have thought that if previous efforts failed, that is a Divine sign that Hash-m wants the person to remain ill or maimed. The verse teaches that the failed efforts should not be construed as such, and the doctor may repeatedly attempt to cure the person.
(c) RABEINU CHANANEL (cited by the Moshav Zekenim) explains that one might have thought that a doctor is prohibited to heal with strong medications, because the medications might adversely or mortally affect the person being treated. The verse teaches that the doctor may practice medicine to the best of his ability, as long as he genuinely intends to help the person. This is also the approach of the RAMBAN (in TORAS HA'ADAM, p. 41).
(d) TOSFOS HA'ROSH in Berachos (60a) cites RABEINU YAKOV of Orleans who explains that the verse permits a doctor to receive wages for his services. Normally, one is not permitted to take money for a Mitzvah, such as for returning a lost object (see Nedarim 38b). A doctor, however, is permitted to take wages for his services.
(e) The TUR (beginning of YD 336) explains that the Gemara is not teaching that a doctor is permitted to heal, but that it is a Mitzvah for him to heal. He should not refrain from healing out of fear that he might accidentally harm the person he is trying to help. Rather, he should view it as a Mitzvah and he should offer his services wherever possible.
The Ramban (in Toras ha'Adam) takes this further and says that it is an obligation for a doctor to heal because of "Piku'ach Nefesh," the obligation to save a person's life. (The obligation is the doctor's when the patient wants his services. However, the patient can act with Midas Chasidus and choose not to turn to doctors for help; see Insights to Berachos 60:1-2.)

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2) UNEMPLOYMENT COMPENSATION
QUESTION: The Mishnah states that the Mazik must pay the Nizak "Sheves" by compensating him for the time that he was unable to work as a result of the wound. The amount of the compensation of "Sheves" is based on the wages that the injured person could have earned as "Shomer Kishu'im" (a gourd-guard).
The Gemara asks why he should receive only the wages of a Shomer Kishu'im if -- when he is healed -- he is able to earn higher wages? He can earn higher wages by drawing water (if his leg broke) or by delivering mail (if his arm broke; Rashi). The Gemara answers that since the payment for the loss of the person's limb was included already in the payment of Nezek, it is appropriate for the Nizak to receive as Sheves only the wages of a Shomer Kishu'im.
Why is it appropriate that the victim should receive only the low wages of a Shomer Kishu'im simply because he received the payment of Nezek? The Nezek takes into account the fact that after he broke his arm he no longer could work at his regular vocation, such as cutting diamonds. However, he still could earn more than a Shomer Kishu'im by delivering mail (if his arm broke, or by drawing water if his leg broke). Therefore, since the illness prevents him from earning the wages of a water-drawer, the Mazik should have to pay him the wages of a water-drawer for the days that he is sick.
ANSWERS:
(a) TOSFOS (DH d'Chi Mitpach) explains that when the Gemara says that when the person is healthy he can work as a water-drawer (or a messenger to deliver mail), it means that before he was injured he was fit to do such work. Consequently, the Mazik should be required to pay the Nizak for the loss of wages that the Nizak incurred by not being able to work at his original vocation.
The Gemara answers that the payment of Nezek already takes into account that the Nizak no longer can work at his original vocation, and that all he is fit now to do is guard gourds. Therefore, the additional payment of Sheves covers only the loss of the Nizak which he incurs by not being able to guard gourds during the time that he was recovering from the wound. This is also the way that the RAV ABA'D (the father-in-law of the RA'AVAD) explains the Gemara, as cited by the BA'AL HA'ME'OR. This seems to be the intention of RABEINU CHANANEL as well.
The RASHBA asks that according to this explanation, why does the Gemara give water-drawing and mail-delivering as two examples of vocations of a person who was not injured? A person who has full use of all his limbs can be a diamond-cutter or work at any other high-income profession!
The Rashba answers that the Gemara gives examples of common vocations. According to Tosfos, when a person loses his hand, he is not fit even to deliver mail since mail-carriers use their hands as well.
(b) The Rashba cites the RA'AVAD who explains that even after the person recuperates, he is fit to draw water or to deliver messages, as the simple reading of the Gemara implies. Nevertheless, he is paid Sheves as a Shomer Kishu'im since, normally, a person who is maimed takes a lowly job such as that of a Shomer Kishu'im. The Ra'avad apparently means that if the Nizak -- after he recuperates -- chooses to deliver messages, Beis Din does not assume that this reveals retroactively that he could have delivered messages from the moment he was maimed had he not been bedridden due to his wounds (and therefore the Mazik must pay, as Sheves, the wages of a mail-deliverer). Rather, Beis Din assumes that at the moment he was maimed he probably would have become a Shomer Kishu'im, and his "promotion" to the job of delivering messages is viewed as an increase in salary. Therefore, the Sheves is assessed only as the wages of a Shomer Kishu'im, since Beis Din assumes that this is what the Nizak would have been doing had he been well and not ill.
This may also be the intention of RASHI (DH Azil, and DH Midas ha'Din, as the printed version of Rashi reads, without the emendations of the Maharshal and the Bach), as the MAHARSHA implies.
(c) The BA'AL HA'ME'OR explains that the Mazik does not have to pay Sheves for any vocation other than for the wages the Nizak was earning until the time of the injury. Even if the Nizak can work as a water-drawer after the injury, this is not a vocation that he chose for himself before the injury, and therefore the Mazik does not have to pay for the losses incurred by the Nizak by not being able to draw water while he is ill. The Mazik must pay only for the losses incurred by the Nizak's inability to cut diamonds (if he was a diamond cutter), but this was included in the payment of Nezek (which takes into account the fact that the Nizak can no longer cut diamonds). Why, then, does the Mazik pay Sheves even for the wages of a Shomer Kishu'im if the Nizak did not have that vocation before he was injured?
The Ba'al ha'Me'or answers that in theory it was possible for the Nizak to have been a Shomer Kishu'im at the same time he was a diamond cutter. Therefore, that job is viewed as a possible source of income of the Nizak until he was injured. In order to make up for that lost source of income, the Mazik pays Sheves, since the wages the Nizak could have earned by watching gourds is not included in the payment of Nezek.
The logic of the Ba'al ha'Me'or seems to be as follows. The loss of income suffered by the Nizak because he could have drawn water had he not been bedridden is considered an indirect effect of the damage, since the Nizak was not a water-drawer at the time at which the Mazik caused him to become sick. The only loss which the Mazik directly caused the Nizak is that he stopped he from earning money as a diamond cutter (or from whatever vocation he had before the injury). If the Torah teaches that an extra payment of Sheves is collected for the Nizak, that Chidush at least should be limited to an occupation which the Mazik directly stopped the Nizak from doing. Therefore, Beis Din looks for the type of occupation which the Nizak could have done (at least potentially), together with his normal work, before he was injured. This is what the Mazik directly caused the Nizak to lose, aside from the compensation of Nezek that he must pay. (Of course, if the Nizak -- after he recovers from his injury -- cannot even be a Shomer Kishu'im (for example, he was blinded), the Mazik does not have to pay him the Sheves of a Shomer Kishu'im but rather the Sheves for work that a blind person could do, which a healthy person can do at the same time as his normal work, as Rava says later on the Daf.)
(d) TOSFOS RABEINU PERETZ writes that the main payment of the Mazik is Nezek, and the other payments are only "extra penalties." Therefore, it is enough to make the Mazik pay Sheves as if the Nizak was a Shomer Kishu'im; he does not have to pay according to what the Nizak is actually able to do after he recovers.
The logic of Tosfos Rabeinu Peretz is similar to that of the Ba'al ha'Me'or. The only "true" payment the Nizak deserves is Nezek (and Boshes), just as a person receives only Nezek when he is damaged by someone's animal. With regard to all of the other payments, to a certain degree the Mazik is considered only an indirect cause of loss to the Nizak. Nevertheless, the Torah requires that when a person causes bodily damage to another, he must pay all of the five payments as added penalties. Since those payments are only added penalties, Beis Din is lenient with the payment of Sheves and requires only that the Mazik pay the Nizak as a Shomer Kishu'im.