486 Analyses of Books. [August, 
This description agrees with that of one of the species of 
Vorticella, the “ two little horns ” being the optical expression of 
the cilia imperfectly seen. 
Then follow the observations of Sir E. King, 1693 ; John 
Harris and Stephen Gray, 1696 ; Henry Baker, 1742- — 1751 ; and 
M. F. Ledermuller and O. F. Muller, to whom we are indebted 
for the first attempt to classify these minute organisms. In the 
long interval between the publication of Muller’s “ Animalcula 
Infusoria,” and the appearance of Ehrenberg’s world-famed 
treatise, a considerable number of investigators occupied them- 
selves in the study of these minute organisms. In 1838 the 
result of fourteen years’ study, entitled “ Die Infusionsthierchen 
als Volkommene Organismen,” appeared, a work which even 
now ranks as classical. The imperfection of Ehrenberg’s optical 
appliances led him to attribute to these minute organisms a far 
more complex structure than they have since been found to 
possess. Their very simple organisation was first noted by 
Dujardin, in 1841, and from that period to the present time, 
owing to the successive improvements of the microscope, and 
the increased diligence of observers, one discovery has followed 
another in quick succession. 
The five succeeding chapters are devoted to introductory 
matter, the second containing an account of the sub-kingdom, 
Protozoa, and the next the Nature and Organisation of the 
Infusoria ; this chapter concludes with some valuable informa- 
tion as to the mode in which the microscopical observations are 
to be conducted. As must be expeCted, numerous difficulties are 
encountered in carrying on observations with the very high 
powers needed in examining some of the- more minute forms. 
Mr. Kent remarks that the thinnest cover glass made is incon- 
venient on account of its extreme brittleness and rigidity ? and 
hampers progress in a most provoking manner, and materially 
restricts the limits of clear vision. The author, as a substitute 
uses very thin films of talc, which for perfect evenness and 
transparency will compare favourably with the finest manufac- 
tured glass. With the employment of these talc-films the in- 
vestigation of Infusoria with the i-i6th, i-25th, or even the 
i-50th inch objectives becomes a comparatively easy task. The 
material in question possesses the further advantage of bending 
readily, and permitting the objeCt-glass to be brought closedown 
on the more remote objeCts in the microscopic field, while it may 
be cut with scissors to any required size or shape. 
A description and figure is given of the moist slide employed 
by Messrs. Dallinger and Drysdale in prolonged observations, 
and also the way of making use of it. 
It would hardly be supposed possible to preserve permanently 
so delicate an organism as an infusorial animalcule ; nevertheless, 
this has in many instances been successfully accomplished. 
Osmic acid is the reagent which has been found most effectual. 
