Galen opens his treatise on the natural faculties by asserting that the body possesses innate powers—attractive, retentive, and expulsive—that govern physiological processes. Rather than relying on abstract theory, he grounds his argument in observable phenomena: the way a drug draws a specific humor, or how the lodestone attracts iron. The translation by Arthur John Brock, a physician himself, preserves the combative tone of Galen's polemic against rival medical sects, especially the followers of Asclepiades, who denied such faculties.

The Polemical Structure

The text is structured as a sustained argument against Asclepiades and his school. Galen repeatedly accuses his opponents of betraying the evidence of the senses. In one passage, he writes that Asclepiades “bids us disbelieve our senses” when the observed facts contradict his hypotheses. This adversarial framing shapes the treatise: each chapter introduces a physiological claim, then defends it by attacking alternative explanations. Galen’s rhetoric is sharp, calling his opponents’ arguments “sophisms” and “idle talk.” The reader is drawn into a forensic debate where clinical observation serves as the ultimate witness.

Diction of Attraction and Resistance

Galen’s vocabulary centers on verbs of pulling, drawing, and expelling. Words like helkein (to draw) and kenoun (to empty) recur throughout. He describes drugs as “attracting their proper humor” and the body as “expelling waste.” This diction is not merely descriptive but carries theoretical weight: by insisting on active faculties, Galen counters the mechanistic view that all bodily motions result from passive particle collisions. The translator Brock notes in his preface that he has rendered such terms with care, often adding explanatory footnotes to clarify the Greek originals for modern medical readers.

Clinical Evidence as Rhetorical Weapon

Galen frequently appeals to everyday medical experience. He cites the seasonal variation in humors—more yellow bile in summer, more phlegm in winter—and the differing effects of purgatives on young versus old patients. In one example, he argues that if a drug merely generated a humor rather than attracting it, it would worsen the disease. He points to the visible success of treatments: “It is clearly seen to benefit many.” Such appeals are designed to shame his opponents into accepting the evidence of practice over abstract theory. The excerpts show Galen using concrete cases—like the treatment of jaundice with scammony—to ground his theoretical claims.

The Translator’s Role

Arthur John Brock’s translation, completed in 1916, reflects his own medical background. In the preface, he acknowledges help from classical scholars and biologists, aiming to bridge the “humanities” and modern biological science. His footnotes often draw parallels between Galenic terms and contemporary medical vocabulary. For instance, he highlights words that have survived into modern medical usage. Brock’s introduction and synopsis of chapters provide a roadmap for readers unfamiliar with ancient medicine. The translation itself is direct, preserving Galen’s periodic sentences and argumentative tone, while the facing Greek text allows comparison with the original.

Readers approaching this work should attend to the interplay between observation and theory. Galen’s arguments are rooted in clinical detail, but his conclusions are shaped by a teleological worldview. Brock’s edition, with its scholarly apparatus, offers a window into both ancient medical reasoning and early twentieth-century efforts to reconcile it with modern science. The treatise rewards careful reading of its examples, which reveal the empirical basis for Galen’s enduring influence.