医者と懇意な彼は先刻診察所へ這入った時、物珍しさに、それを覗かせてもらったのである。

He, who is close with doctor, entre consulting room some time ago, and looking that because curiosity.

添削

He, who is close with a doctor, entered the examination room some time ago, and out of curiosity, asked to take a peek inside.

He, who is on familiar terms with a doctor, had entered the clinic a while ago and, out of curiosity, asked to take a peek inside.

その時八百五十倍の鏡の底に映ったものは、まるで図に撮影ったように鮮やかに見える着色の葡萄状の細菌であった。

Then, it was seen the mirror bottom in eight hundred fifty times, alike a bacteria of a grape shape with vivid color like take picture.

添削

The image seen at the bottom of the 850x magnification mirror was that of a grape-shaped bacterium, with vibrant coloring that looked as if it had been vividly captured in a photograph.

What was reflected on the bottom of the 850x magnification mirror at that time was a grape-shaped bacterium with vivid coloring that looked as if it had been photographed with remarkable clarity.