(b) no half- monthly payment shall in any case exceed the amount, if any, by which half the amount of the monthly wages of the workman before the accident exceeds half the amount of such wages which he is earning after the accident. Explanation.-- Any payment or allowance which the workman has received from the employer towards his medical treatment shall not be deemed to be a payment or allowance received by him by way of compensation within the meaning of clause (a) of the proviso.