Detailed Instructions: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Q: Passage: Before, during and after his mayoralty, Sharpe played a major role in promoting sanitary reform, often meeting considerable opposition and needing to use his oratorical, political and persuasive skills to the full. A campaign to deal with the problems had been initiated in 1847 by two Lancaster doctors, Thomas Howitt and Edward Denis de Vitre.  Sharpe joined them, drawing extensively on his experience of having accompanied Professor Richard Owen (born and educated in Lancaster) on his tour of inspection of the town in 1844. In 1848 Robert Rawlinson, also from Lancaster, was appointed as local surveyor, and published a further report that recommended new sewers and drains and the construction of a waterworks. Although Sharpe agreed in principle with the report, he was not satisfied with its details. Later that year, which was during his mayoralty, he travelled to London with the town clerk and a former mayor to meet representatives of the General Board of Health, including its chairman, Lord Morpeth, and its secretary Edwin Chadwick.  As a result of this meeting, the Board of Health appointed James Smith from Scotland as an inspector, and commissioned him to produce a further report on Lancaster's problems. Smith's investigation took place in January 1849, and his report was received in July. In his conclusions, Smith noted that Lancaster was favourably situated to provide a healthy environment for its inhabitants, and that this could be achieved by "a complete and constant supply of pure and soft water, and ... a thorough system of drainage and sewerage". Subsequently, an Act of Parliament gave approval for these measures to be carried out, and in 1852 royal assent was given for the waterworks to be constructed. Delays, disputes and controversies continued, until the waterworks was eventually opened in 1855, when work on the drainage and sewage systems was already under way.  This enabled underground pipes for the two systems to be laid simultaneously. Sharpe had played a significant part in arranging Queen Victoria's visit to Lancaster in October 1851, and with Paley designed four triumphal arches for the occasion.  He also took part in the proceedings on the day, escorting the Queen, Prince Albert, and the Prince of Wales (the future King Edward VII) to the top of the castle tower.In 1859 Sharpe was appointed as a Justice of the Peace for Lancashire and for Denbighshire. Shortly after his return to Lancaster in 1866 he again became involved in local politics.  In 1867 the constituency of Lancaster was disfranchised because of corruption, and so lost its two members of parliament. Sharpe wrote a long letter to Benjamin Disraeli (Chancellor of the Exchequer, and responsible for the Reform Act of that year), arguing the case for reinstating Lancaster as a parliamentary constituency, and putting forward his own proposals for electoral reform.  His letter received no reply, and Lancaster remained without parliamentary representation for the next 20 years.
A:
What was the last names of the two Lancaster doctors who initiated a campaign to deal with the problems?