a period in a paragraph? kill it!

Just pulled down "Guys & Dolls", my book of Damon Runyon stores to read to mother and child during feedings and was struck, as they say, on the third page of the first story when, out of the blue and with no warning, the author used a period to end a sentence before we got to the end of the paragraph, and I says to myself "what kind of a Philistine would do such a thing", and finding no answer scratched out the offending article and kept going.