Abstract This paper focuses on Edmund Parkes’ Manual of Practical Hygiene, Prepared Especially for Use in the Medical Service of the Army (1864), a text that would become the standard within British military medicine for decades to come. Within Parkes’ Manual, I argue, we can see the confluence of three streams of thinking – each beginning in the 1830s and 1840s – that led to a new orthodoxy on race-medicine in the Victorian period. The first flowed from an ‘avalanche of numbers’, to use Hacking’s phrase, concerning military medical statistics, a set of seemingly objective data that made race medically ‘real’ in a form that had not been evident before. The second was the solidification of fixist conceptions of race after the collapse of what George Stocking called the ‘Prichardian paradigm’ in British ethnology. The third involved what has become known, in the history of medicine, as the ‘doctrine of specific etiology’, the idea that the cause of certain diseases was the cause of each of those diseases alone. These three factors together led to a novel set of racial arguments, one that assumed the reality and permanence of race and that explained differences in susceptibility and immunity not, as was common earlier, in terms of climatic habituation, but rather in terms of the fixity and peculiarity of internal differences.