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POPULAR SCIENCE REVIEW. 
DiatomacecB consists in illuminating tlie object by means of oblique light, 
so arranged that the reflected bundle strikes it at an angle of 45°. This 
method he considers most unsatisfactory. Here then are three other ways 
of illuminating, say Navicula. The Jirst consists in passing solar light 
directly through the object, and protecting the retina by a blackened glass 
placed over the objective. This mode, he says, gives the striae very well. 
The second consists in employing the solar spectrum, reflecting from the 
mirror the light between orange-yellow and greenish-yellow. The third 
consists, whatever may be the magnification, in illuminating the Navicula 
directly, as opaque objects are illuminated, but by a somewhat different 
process : we place, says the author, an equilateral prism on the level of the 
stage, and then we direct a bundle of rays — either white or spectral — be- 
tween the preparation and the object, and we see the striae black upon a 
coloured ground. These processes do not require great experience for their 
satisfactory employment, but may readily be adopted by the amateur. These 
methods, says the author, have given me valuable assistance in the exami- 
nation of Diatomacece, and they are equally applicable to other substances. 
He suggests the following substitute for solar light : — A hemispherical con- 
denser is placed in front of a conical reflector, and a lamp is set between 
the two. This lamp should be a magnesium lamp, or a lamp in the centre 
of whose flame a cylinder of solid magnesia has been placed. 
The genus Cochliostema forms the subject of an interesting paper, recently 
published by Dr. Maxwell Masters in the Gardener s Chronicle (pp. 264, 
323). It would be impossible, in the brief space at our disposal, to do 
more than refer to Dr. Masters’ memoir, the anatomical details being too 
numerous and complex to enumerate them shortly and without figures. 
We may remark, however, that the author demonstrates very clearly, that 
there is more to be seen, on minute examination, than M. Lemaire’s descrip- 
tion would lead one to suppose. 
The Natural History of Blights. — A number of questions recently put by 
Dr. Gavin Milroy, an active member of the Epidemiological Society, have 
been replied to by the Rev. M. J. Berkeley. The answers are of the utmost 
importance, both to the botanist and the student of hygiene and epidemics, 
and are published in recent numbers of the Gardener’’ s Chronicle. In refer- 
ence to the theory of Hallier, viz. that cholera is produced by a species 
of fungus growing on diseased rice, the Rev. J. M. Berkeley remarks : — 
^‘I do not believe in Hallier’s views of the connection of cholera with 
parasites on rice. I am taking great pains to ascertain what are the rice 
parasites. I believe Hallier’s notions to be entirely theoretical. That some 
cutaneous disorders arise from fungi is pretty evident, but there is nothing 
to show that fever, or other infectious or contagious diseases, arise from the 
same cause. It was supposed that diphtheria depended on a fungus, but I 
have examined diphtheritic membranes in which there was no fungus.” In 
reference to the mode of entrance of the parasitic fungus, Mr. Berkeley 
writes : — In the bunt the whole process is traceable ; the parasite obtains 
admission from without, and the spawn traverses the young plant. In 
plants impregnated by myself I have seen the stem as well as the grain 
affected ; but I never saw this in the fields. The potato murrain, again, is 
distinctly traceable in affected tubers, the threads seeming to have a power 
