PRESIDENT’S ADDRESS TO MANCHESTER MICRO. SOCIETY. 95 
which gave better correction with wide apertures; and it was soon 
afterwards discovered that the correction for spherical aberration 
depended largely upon the thickness of the front lens. The 
introduction of the principle of “homogeneous immersion” 
brought the microscope to its present high state of perfection. 
This short sketch will enable you to understand that, although 
lenses were used for the investigation of nature from a very early 
period, very little could have been known previous to the beginning 
of the seventeenth century about the minute structure of natural 
objects, and that at that time the introduction of the compound 
instrument gave an impetus to microscopical research, which was still 
carried on to a great extent by means of simple lenses of an improved 
character. We find that during that century Malpighi discovered 
the corpuscles in the blood, and witnessed some forms of capillary 
circulation. He discovered the Malpighian bodies in the kidneys 
and spleen. Swammerdam invented the process of injecting the 
blood vessels with a coloured solidifying fluid, and investigated 
the minute anatomy of the bee, the ‘‘ May-fly,” and some other 
insects with considerable success ; and then Leeuwenhoek came 
upon the scene as the pioneer of modern microscopical research. 
He confirmed the truth of Harvey’s discovery of the circulation of 
the blood, by witnessing its passage from the arteries to the veins 
through the capillaries of several animals. He traced the anatomy 
of the flea, and its mode of reproduction, and disproved the 
assertions of his predecessors that it was produced from sand or 
dirt, and that animals of high organisation could be “ produced 
spontaneously or bred from corruption.” He also traced the 
mode of reproduction of some other animals; and whilst he con- 
firmed the doctrine previously announced by Redi, the Italian 
naturalist, Ommne vivum ex vivo, he inculcated another, Ome 
vivum ex ovo. He appears to have known that yeast contained 
“ slobules,” but the imperfection of his lenses did not allow him 
to discover that these globules were living cells reproducing them- 
selves by gemmation and fission, and that the lowest animals, the 
Protozoa, had a similar mode of reproduction. He was the dis- 
coverer of the Rotifera (wheel animalcules), and their capability of 
resuscitation after the drying up of the water they inhabit. 
Of the anatomy and physiology of plants little was known 
previous to the discovery by Grew, in 1676, of the functions of 
the stamens and pistils. That plants had sexes was known from 
a remote period, for, according to Herodotus, the Babylonians 
recognised the difference between male and female date palms, 
but the organs of reproduction were unknown. ‘The function of 
pollen appears to have been first noticed by Samuel Morland in 
1703, and in 1736 Linnzus published his sexual system of 
botanical classification. He failed, however, to recognise the 
