In 1928, Van der Hoog was asked to travel to
Jeddah in the
Hejaz to lead a team of Egyptian and Syrian doctors. He quickly accepted the invitation, seeking to leave the routine of his Dutch life in favour of new adventures. He arrived in September, the
Ministry of Foreign Affairs not having discussed his employment with the Ministry of the Colonies. After the latter expressed its concern with Van der Hoog's temperament, "warning [Van der Meulen] of the adder [he] might be clasping to [his] breast", the consul spoke with the doctor and deemed him well-suited for the task. Van der Hoog was tasked with research and vaccine preparation at a Jeddah hospital. Often tasked with treating soldiers, policemen, and civil servants, van der Hoog later described the experience as miserable. He later recalled the streets being filled with oppressive black clouds of flies, swarms of stray cats eating amidst piles of feces, and having only a bowl and rusted medical instruments to practice. He became concerned with the prevalence of water-borne illnesses, especially given the limited access to water in the area. As he remained in the Hejaz, Van der Hoog became interested in
Mecca and the purported healing benefits of water from the
Zamzam Well. He was unable to obtain a sample personally, as the city was closed for non-Muslims, but samples obtained through an assistant showed lower microbial concentrations than water collected from the
canal of Zubaidah. He soon converted to Islam, which Van der Meulen attributed to his desire to learn about the well as well as to find material for publication in the Dutch press. This conversion was poorly received by both the Christian and Muslim residents of Jeddah, in part due to its perceived suddenness, and Van der Hoog was ostracized. The issue received coverage as far afield as the Dutch East Indies, where the
Soerabaijasch Handelsblad speculated that he had simply professed conversion to gain access to Mecca. Desiring nonetheless to travel to Mecca, Van der Hoog wrote to King
Ibn Saud to announce his conversion and request permission to enter the holy city. In his response, Ibn Saud congratulated Van der Hoog on his conversion, but required of him, "Accomplish your duty and be faithful in performing the prescribed five daily prayers in one of the mosques in Jedda. And when you have lived a year as a devout Muslim, then come and perform your duties as a pilgrim to the Holy Shrine in Mecca." ==Return to the Netherlands==