A General Index to the Philosophical Transactions, from the first to the end of the seventieth volume
full text facsimile available for free download at Google Books
In the late 1700's, Paul Henry Maty, a secretary of the Society, created a general index to Philosophical Transactions, seventy volumes to that point. Maty lists all of Leeuwenhoek's contributions, by volume, and the index is available complete from Google Books.
Maty, Paul Henry. A general index to the Philosophical transactions, from the first to the end of the seventieth volume. Royal Society, London, 1787.
Dobell says (p. 389) that Maty has indexed "more or less accurately". Ten times, Maty breaks articles that are listed once in the journal's table of contents into multiple articles, one for each topic.
For example, this entry in the table of contents:
Extract of a Letter Written to the Publisher by Mr. Leewenhoeck from Delft, April 21. 1676; Concerning the Texture of Trees, and Some Remarkable Discovery in Wine; together with Some Notes Thereon
is two items on Maty's list, but both listed as starting on the same page, 653:
On the texture of trees, with notes thereon
A remarkable discovery in wine, which notes thereon
Thus, Maty has about ten more entries for Leeuwenhoek, 122, than the journal's actual tables of contents, which has 111 (and is missing the famous Berkelse Meer letter of September 7, 1674). Nevertheless, Maty's Index remains the best available.