Pm | 
NATURE 
673 
AucusT 29, 1912| 
causing larvae of the human Agchylostoma to live for | convenient or more accurate methods of effecting 
a time in puppies. 
He has set himself the task of writing a life-history 
of Agchylostoma duodenale from a scientific point of 
view, and traces the development of the parasite out- 
side the body, while he also conceives it to be his 
duty to censure many previous authors for their errors. 
He finds that nematodes may be kept unchanged for 
years in undiluted glycerine, and that their eggs and 
larvee can be best preserved by using hot alcohol. 
In order to prevent the decomposition of faeces used 
as a culture medium, he recommends the addition of 
an equal part of powdered animal charcoal, for this 
mixture prevents harmful effects to the eggs and 
larvee. 
He disagrees with other observers who state that 
the mature embryo breaks the eggshell by knocking 
against it with its head and tail, for he finds that the 
shell bursts of itself, and in so doing throws out the 
embryo passively. The faces of natives of warm 
climates present a more favourable medium for the 
development of larvz than the excreta of those who 
live entirely on meat or on vegetables. Oxygen, a 
constant temperature which may, however, be as low 
as 50° F., or as high as 105° F., and moderate mois- 
ture are the factors necessary for the development of 
young larve, while the proper element for mature 
larvee is water, which they eagerly enter as soon as 
they can, and in water they can live for months be- 
cause they no longer require any food. Prof. Looss 
’ finds that sunlight alone does not act injuriously upon 
the eggs, provided the temperature is not also raised. 
While studying the migratory instincts of larvee in 
his laboratory in Cairo, the author, by a not unhappy 
accident, found himself infected by a drop of culture . 
fluid containing some hundreds of lively larvae, which 
fell upon his hand. Experiments patiently conducted 
on himself, on volunteers, and on young puppies 
eventually solved the mystery of how mature larve 
enter the skin, either by the hair foliicies or by the 
horizontal fissures between the scales of the epidermis, 
and how they then migrate to the duodenum of the 
host. The time which elapses between infection by the 
mouth and the earliest date when eggs are found in 
the victim’s faeces is thirty days, whereas in infection 
by the skin it varies from forty-five to seventy-four 
days. His great discovery of infection by the skin 
has of late years been amply confirmed by many 
observers. Among the most important we may men- 
tion Schaudinn, Lambinet of Belgium, and in 
America, Claude Smith, Stiles and Ashford and King. 
Passages on which the author desires to lay 
emphasis appear, as in German literature, in large 
spaced print. 
The plates from Prof Looss’s masterly drawings 
have been faithfully reproduced in Frankfurt, and add 
considerably to the value of the book 
THE MICROSCOPIC DETERMINATION 
OF MINERALS. 
HE identification of a mineral fragment by 
means of the microscope, to be beyond 
doubt, must be based upon some quantitative test, 
such as a measurement of the refractive indices, or, 
in the case of doubly refractive substances, the 
amount of double refraction and the relation of the 
extinction directions to the crystalline form, or, in 
that of biaxial substances, a measurement of the 
angle between the optic axes. Recent years have 
witnessed great progress in the discovery of more 
1 *The Methods of Petrographic-microscopic Res-arch, their Relative 
Accuracy and Range of Application.” By Fred. Eugene Wright. Pp. 204+ 
1 plates+118 figs. (Washington, D.C.: Carnegie Institution of Wash- 
ington, rorr.) 
NO. 2235, vot. 8al 
| considerably, as 
such measurements, and almost equal progress in the 
design of the instruments and accessory apparatus. 
So rapid has been the advance that it has outpaced 
the text-books. Petrologists and all who may have 
occasion to identify minerals from chance fragments 
will therefore feel grateful to Dr. F. E. Wright tor 
the admirable treatise in which he describes in detail 
and discusses with critical acumen the various 
methods and devices available. Dr. Wright is him- 
self responsible for no mean share in the progress 
that has been made, and it is an excellent feature of 
the volume that he is in a position to write of almost 
every method or piece of apparatus from first-hand 
experience in the Geophysical Laboratory; the pages, 
in fact, teem with those practical hints and sugges- 
tions which prove so useful to the worker. 
The scope of the work is satisfactorily complete. 
A lengthy introduction includes an adequate dis- 
cussion of the principles of microscopic vision so far 
as they apply to the particular case of the petrological 
instrument; the various aberrations and their correc- 
tions are explained, and descriptions are given of 
some recent instruments. It is pleasant to find that 
full credit is given to Mr. A. B. Dick for his inven- 
tion of the system of simultaneous rotation of the 
polarising and analysing Nicols which has been 
adopted in all the best forms of petrological micro- 
scope; Continental writers have overlooked his in- 
contestable claims to priority. Dr. Wright prefers 
an adaptation of Mr. Dick’s first suggestion, viz. a 
vertical bar rigidly attached to the circles carrying 
the Nicols, instead of the system of gear-wheels in 
general use, fearing that the backlash in the latter 
might introduce appreciable error in delicate work. 
The first chapter deals with the physical characters 
which do not entail measurement, such as colour, 
crystal habit, dispersion of the optic axes, &c. The 
fact that there is still no recognised standard for 
gauging colour is dwelt upon, and a description is 
given of the Ives calorimeter, which consists of three 
filters rotated by means of an electromotor, the depth 
of each tint being varied at will by means of movable 
shutters. Mention might have been made of the 
Lovibond tintometer, which is based on the same 
fundamental principle, and, though not so accurate, 
is a much simpler piece of apparatus. The difficulty 
of describing a tint is one that affects us all in our 
everyday affairs, and it would be an inestimable boon 
if precision could be given to the colour terms in 
popular use. In the second chapter we pass to the 
measurement of refractive indices. Thanks to Prof. 
Becke’s discovery of the phenomenon known as the 
bright-line effect, it is possible to obtain a value 
which with care may be as accurate as two units in 
the third place of decimals; Dr. Wright adds the 
useful warning that the phenomenon may be masked 
if the dispe-sion of the mineral and the liquid differ 
not infrequently happens. The 
announcement of the discovery of a new, highly re- 
fractive liquid, ranging from 1-790 to -1-960, will 
arouse great interest; it is a mixture of methylene 
iodide, antimony iodide, arsenic sulphide, antimony 
sulphide, and sulphur, but complete details are 
promised in a paper yet to be published. 
In the third chapter the determination of double 
refraction by means of wedges, various forms of 
which are described, is discussed, and it is pointed 
out that the most serious source of error lies in the 
measurement of the thickness,of the fragment under 
observation. In the fourth chapter the methods of 
determining extinction angles are discussed with a 
wealth of mathematical detail, which is of great help 
in understanding the phenomena presented. Atten- 
