Wrote Letter L-544 of 1716-11-05 to Herman Boerhaave about the size of sperm from rams, cod, and ling, little animals from rain water and soil, and blood in arteries and veins

November 5, 1716
Standard reference information
Leeuwenhoek's number: 
Collected Letters volume: 

Text of the letter in the original Dutch and in English translation in Alle de Brieven / The Collected Letters is not yet available at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript is lost.

Continuing his research disproving spontaneous generation, Leeuwenhoek investigated the size of sperm and their occurrence in the epididymis of a ram as well as the number of spermatozoa in the soft roe of a cod and a ling. To learn more about how the sperm could generate so quickly, Leeuwenhoek turned to microbes from rain water and soil and their multiplication. Responding to another researcher, Leeuwenhoek affirmed that arteries and veins have an opening only near the heart. There is no blood outside of blood vessels.

He begins by responding to Boerhaave's question from a previous letter.

Your Honour asks me whether I have seen a difference in the size of the little animals in the male seed  of animals.