169 
At the end of five vears he found the willow weighed a little over 
169 Ibs. (169 & circiter uncias tres’’). He did not compute the 
weight of the leaves that fell off, each of the four autumns. The 
soil and vessel weighed the same as at the beginning, therefore, 
the wood, bark, and roots had gained 164 Ibs. van Helmont 
concludes from this that carbon is made only of water. It is this 
experiment that Singer says was “pirated” from Nicholas of 
Cusay (dav, NowZ1 js 
In this chapter van Helmont records that this same gas 1s a 
product of the fermentation of wine. It is the first description 
of carbon dioxide. 
42. Hooke, ROBERT. 
Micrographia: or Some physiological descriptions of minute 
bodies made by magnifying glasses . . . 1665. 
This famous work is the earliest landmark in the history of 
microscopy. The illustrations, as accurate as they are beautiful, 
have been credited to Sir Christopher Wren. Hooke was the first 
user of the word “cell” to refer to the units of anatomical 
structure. 
43. LEEUWENHOEK, ANTONY VAN. 
Ontledingen en ontdekkingen van de cinnaber naturalis, en bis- 
poeder, 1686. 
Includes: Vervolg der brieven, 1688; Send-brieven ... 1718. 
In addition to a vast amount of work on animalculae and plant 
histology, van Leeuwenhoek made many discoveries of importance 
to medicine. He was the first to describe the spermatozoa, to see 
protozoa, ete. 
44. LEEUWENHOEK, ANTONY VAN. 
Opera omnia. 1695-1719. 4 vols. 
Vol. 1. Arcana naturae. 
First edition in Latin. 
Leeuwenhoek constructed his own microscope and found new 
marvels in all nature. He gave the first complete account of the 
red blood corpuscles, found microdrganisms in the teeth, and dis- 
covered the existence of bacteria. 
