**Core Concept**
The Oakley-Fulthorpe procedure is a laboratory technique used to detect and isolate the causative agent of a bacterial infection, specifically in the context of blood culture and serological testing. This technique involves the principle of diffusion and its application in microbiological investigations.

**Why the Correct Answer is Right**
The Oakley-Fulthorpe procedure is a method of double diffusion in one dimension, where a sample of serum or other biological fluid is placed on a solid medium, such as an agar plate, and allowed to diffuse. This process allows for the detection of specific antigens or antibodies in the sample, which can then be identified and isolated using various microbiological techniques. The double diffusion aspect of the procedure involves the simultaneous diffusion of two or more substances, such as antigens and antibodies, towards each other, resulting in the formation of a visible precipitin line or ring.

**Why Each Wrong Option is Incorrect**
**Option A:** Single diffusion in one dimension is incorrect because the Oakley-Fulthorpe procedure involves the simultaneous diffusion of two or more substances, not just a single substance. This makes option A a fundamental misunderstanding of the procedure.
**Option C:** Single diffusion in two dimensions is incorrect because the Oakley-Fulthorpe procedure is specifically designed to detect and isolate substances in a one-dimensional diffusion pattern, not in two dimensions.
**Option D:** Double diffusion in two dimensions is incorrect because the Oakley-Fulthorpe procedure is a one-dimensional technique, not a two-dimensional one.

**Clinical Pearl / High-Yield Fact**
The Oakley-Fulthorpe procedure is a classic example of a serological test used to detect specific antibodies or antigens in biological fluids. This technique remains an essential tool in microbiological investigations, particularly in the diagnosis of bacterial infections.

**✓ Correct Answer: B. Double diffusion in one dimension**