64 
WATURE 
[May 25, 1871 

subject of importance in meteorological discussions. This 
is a very different thing from what is termed by Mohn 
“état hygrometrigue,? and denotes the chemical com- 
position of the air, as regards moisture, or the weight of 
vapour contained in a hundred parts by weight of air. 
Now, as long as the pressure remains the same, this 
hygrometric quality will be represented by the tension of 
vapour, and, since on the surface of the earth the 
variations of pressure are comparatively small, the vapour 
tension will approximately represent the hygrometric 
quality. If this be borne in mind, the physical significance 
of Mohn’s conclusions will become apparent ; his remark, 
that the charts of vapour tension present a continuity 
and simplicity of distribution of that element, will now 
mean that the distribution of zyfes or kinds of air is of 
avery simple nature. 
We should, in fact, endeavour to find the distribution 
of air of various qualities over the surface of the earth 
just as we should endeavour to trace on the surface of the 
ocean sections of different saltness. But, while on the 
earth’s surface vapour tension will approximately repre- 
sent hygrometric quality, the case will be altered if we 
study strata of different elevations, and therefore of 
different pressures. If for instance, we ascend a moun- 
tain or take a trip in a balloon, the tension of vapour will 
no longer approximately represent the hygrometric quality 
of the air ; but it will be the ratio between the pressure 
of aqueous vapour and that of air, which will truly represent 
the hygrometric quality in those regions. Theseconsidera- 
tions may, perhaps, throw some light upon the formation 
of clouds. If, for instance, air of the same quality 
extends a great way up, we shall have no cloud formed 
in the stratum as long as the rate of decrement of tem- 
perature does not exceed a certain limit ; but when this 
limit is exceeded, there will be a deposition of cloud 
through the lowering of temperature alone, even while 
there is no admixture with air of another quality. 
B. STEWART 



OUR BOOK SHELF 
Veber Entwickelung und Bau des Gehorlabyrinths, nach 
Untersuchungen an Saiigethieren. Von Dr. Arthur 
Boettcher, o. 6. Professor der allgemeinen Pathologie 
und pathologischen Anatomie, a. d. Universitat Dorpat. 
Erster Theil mit zw6lf Kupfer Tafeln. (Leipzig: Wilhelm 
Engelmann, 1871. London: Williams and Norgate.) 
THE successful investigation of the structure of the in- 
ternal ear must always be regarded as the crown and 
glory of histological research, for whilst the structures that 
compose the auditory organ are of extreme delicacy, they 
are enclosed in a bony capsule of such density as to appear 
to bid defiance to all attempts to exhibit them in their 
natura] state. Yet by careful decalcification with dilute 
acids and by immersion in various fluids, as those of Miiller 
Schultze’s solution of chloride of palladium, Cohnheim 
and Gerlach’s solution of chloride of gold, &c., the most 
delicate details have been followed out, and the structure 
of the ear is now almost as well known as that of the eye. 
M. Boettcher’s observations on the labyrinth of adult 
animals have been largely supplemented by his numerous 
examinations of the same part at various periods of foetal 
life, which have led to some interesting results. 
The very earliest rudiment of the labyrinth in the 
mammalian foetus is not yet accurately ascertained, but 
in the embryo of a sheep, of which a sagittal section of 




the head is only a millimetre in length, it appears as a sac 
with a small external opening formed by an inflection of 
the horny layer in close contact with this and oppo- 
site the second visceral arch. The wall of the sac 
is formed by cylindrical cells. In a somewhat more 
advanced stage the vesicle becomes elongated into a tube, 
the upper extremity of which is divided by a fold into an 
internal and smaller cavity—the recessus labyrinthi, 
and a larger, broader cavity, the aqueeductus vestibuli. 
The inferior extremity is pointed, and is in immediate re- 
lation with the rudiment of the cochlea. 
The semi-circular canals are formed by an inflection of 
the wall of the labyrinth vesicle opposite to the recessus 
labyrinthi, the horizontal canal being the last formed. In 
embryoes of 22 cm. long, the several parts above men- 
tioned are more fully formed, and a projection appears, 
the fundus of which is directed towards the brain, which 
is the rudiment of the sacculus rotundus, from which the 
utriculus or sacculus ellipticus soon becomes differentiated. 
The separation of a scala vestibuli from a scala tympani 
in the cochlea is only apparent in embryoes that have at- 
tained a length of 8°5 cm. M. Boettcher clearly shows 
that the recessus labyrinthi found at a very early period 
subsequently becomes the aquzeductus vestibuli, which re- 
mains permanently in connection with the sacculus ro- 
tundus and utriculus, and contains the same fluid (endo- 
lymph) asthey do. The aquzeductus cochleze, on the other 
hand, is a totally different formation, and is in no way 
connected with the interior of the labyrinth. It con- 
ducts a vein, and might more correctly be styled, as Wild- 
berg has suggested, the canalis venosus cochlez. 
In regard to the cochlea, he shows how the canalis 
cochlea, or scala media, is first developed, and how the 
two principal scale (scala tympani and vestibuli) are 
formed by the gradual breaking down of spongy cellular 
tissue on either side of the scala media, and he traces out 
in the most interesting manner the development, chiefly 
from epithelium, of the complicated organ of Corti, in-, 
cluding under this head the so-called habenula perforata, 
the rods, and arched fibres, &c. 
He describes a remarkable ganglionic mass, the gan- 
glion spirale, the section of which is seen in this section of 
the cochlea close to the attached border of the lamina spi- 
ralis. In thisthe cochlear nerve appears to terminate, whilst 
from it fresh fibres take origin, and then, having passed 
through the openings of the habenula perforata, join cer- 
tain cells, some of which are placed outside and some 
inside the arcuate fibres or rows of Corti. The former 
kind of auditory cells are, some of them, seated with a 
broad base on the membrana basilaris, whilst the attenuated 
extremity of the cell runs upwards. Others, however, are 
intercalated with these, which havea broad base attached 
to the membrana reticularis above, and then narrow apices 
interposed between the broad bases of the former. The 
cells that point downwards are Corti’s cells, and are ar- 
ranged in three rows. They possess a centrically directed 
process. The cells that point upwards are the so-called 
hair-cells, which receive this name on account of their 
terminating at both ends in a hair. The membrana basi- 
laris he describes as consisting of a hyaline lamella on 
which is a fibrous layer, both layers having a peculiar 
form of epithelial investment. Beneath its proximal at- 
tachment is a spiral vessel. The development of all these 
parts is carefully traced. A very full account is given of 
Corti’s membrane. He denies the existence of muscular 
elements in Todd and Bowman’s ligamentum spirale. The 
essay concludes with a description of the ultimate distri- 
bution of the auditory nerve. The drawings, which are 
upwards of sixty in number, and in some instances of 
large size, are very beautifully executed. On the whole, 
the work of Boettcher appears to be well worthy the atten- 
tion of microscopists and physiologists, and to contain 
many facts possessing both novelty and interest. 
EB. 
