The Presidents Address. 
no existence ; in fact_, the pTiytiform structure does not come 
from without; but is developed where it is found, and that, 
in essential nature, it is a perversion of a normal process^ a 
degradation of vitality of the cell- elements, and a transforma- 
tion of an animal structure into a lower form of organism^ 
into one which is usually regarded as a vegetable tissue. He 
further states that this morbid change occurs beneath the 
epidermis without breach of the latter, and in the substance 
of the rete mucosum, and that the morbid tissue moves to the 
surface only by progressive growth. Mr. Erasmus Wilson 
believes the perforation of the horny layer of the epidermis by 
a mucedeinous sporule impossible, and regards the cause of 
the development of the phytiform tissue, and consequently of 
the disease, as coming from within, dependent only upon the 
vitality and health of the individual, and independent of 
personal cleanliness and exterior conditions of every kind. 
A more intensely interesting field can scarcely be found 
for the labours of the micro-physiologist than that chosen by 
Mr. Hogg. 
The most important novelty of the year has been the suc- 
cessful application of the spectroscope to the microscope. In 
Mr. Sorby^s first experiments of this class (^Quarterly Journal 
of Science,^ 1865, p. 198) he used such an arrangement as 
could be made with a simple triangular prism. This was 
placed below the achromatic condenser, so that a minute 
spectrum of any transparent object could be examined, and 
the particular rays which it transmitted easily seen. Shortly 
after the publication of Mr. Sorby^s paper, Mr. Huggins sent 
a paper to this Society,^ in which he proposed to adapt a 
spectroscope to the eye-piece of the microscope, so as to enable 
us to view the spectra of opaque as well as transparent objects. 
After this meeting, Mr. Browning suggested to Mr. Slack 
and myself that a direct-vision spectroscope would be the 
most convenient form for this purpose ; and on the 14th 
June he read a paper in which he showed how a compound 
direct-vision prism could be applied to the microscope as an 
eye-piece. The exact form of prism finally adopted was 
determined after communication with, and experiments by^ 
Mr. Sorby. The slit may be either in the focus of the object- 
glass, or in that of the eye-piece or of one of its lenses. 
One of Mr. Sorby's arrangements was to have the slit in 
the focus of the object-glass, and the compound prism between 
them. In using a binocular microscope, this form enables us 
to see the spectrum with both eyes, and also to use a micro- 
meter to measure the position of any absorption bands. It is 
* ' Quart. Journ. Mic. Sci.,' July, 1865, p. 85, 
