with the
minute size and elusive evolutions of these organisms, and with the
limited appliances at Cohn's command. Nevertheless his account of the
life-histories of _Protococcus_ (1850), _Stephanosphaera_ (1852),
_Volvox_ (1856 and 1875), _Hydrodictyon_ (1861), and _Sphaeroplea_
(1855-1857) among the Algae have never been put aside. The first is a
model of what a study in development should be; the last shares with G.
Thuret's studies on _Fucus_ and Pringsheim's on _Vaucheria_ the merit of
establishing the existence of a sexual process in Algae. Among the Fungi
Cohn contributed important researches on _Pilobolus_ (1851), _Empusa_
(1855), _Tarichium_ (1869), as well as valuable work on the nature of
parasitism of Algae and Fungi.

It is as the founder of bacteriology that Cohn's most striking claims to
recognition will be established. He seems to have been always attracted
particularly by curious problems of fermentation and coloration due to
the most minute forms of life, as evinced by his papers on _Monas
prodigiosa_ (1850) and "Uber blutahnliche Farbungen" (1850), on
infusoria (1851 and 1852), on organisms in drinking-water (1853), "Die
Wunder des Blutes" (1854), and had already published several works on
insect epidemics (1869-1870) and on plant diseases, when his first
specially bacteriological memoir (_Crenothrix_) appeared in the
journal, _Beitrage zur Biologie_, which he then started (1870-1871), and
which has since become so renowned. Investigations on other branches of
bacteriology soon followed, among which "Organismen der Pockenlymphe"
(1872) and "Untersuchungen uber Bacterien" (1872-1875) are most
important, and laid the foundations of the new department of science
which has now its own laboratories, literature and workers specially
devoted to its extension in all directions. When it is remembered that
Cohn brought out and helped R. Koch in publishing his celebrated paper
on _Anthrax_ (1876), the first clearly worked out case of a bacterial
disease, the significance of his influence on bacteriology becomes
apparent.

Among his most striking discoveries during his studies of the forms and
movements of the Bacteria may be mentioned the nature of Zoogloea, the
formation and germination of true spores--which he observed for the
first time, and which he himself discovered in _Bacillus subtilis_--and
their resistance to high temperatures, and the bearing of this on the
fallacious experiments supposed to support