The paper extends the analysis of western medicine further in the realm of actual practices involving diagnostic techniques, tools and testing. This would help us understand their role in the practice of modern medicine and its professionalisation. This being the realm where modern medicine and technology came directly into contact with the wider population (beyond the realm of the academic), the paper would bring out the popular perceptions of the power of modern medicine as mediated by these various diagnostic tools and clinical practices in the Madras Presidency. Specifically, the paper will trace the introduction and diffusion of X-ray machines in the Madras Presidency, from early 1900s to early 1930s, through the various policy initiatives made by the colonial government in enhancing the diagnostic capabilities of physicians and surgeons. Also, the paper will examine the reception of this technology by the medical professionals, their hopes and fears of its potential utility and harmfulness in the practices of medicine. The period 1920s and 30s witnessed strong reactions from Indigenous medical practitioners to colonial government’s efforts to reduce their scientific status, and a slow but lukewarm response from the colonial government in according them professional recognition that will license them to practice their medicine. Modern technological tools such as x-ray helped in forcing a resolution over such debates across schools of medicines, and eventually in establishing the supremacy and hegemony of the western medicine over other systems of medicines in India.