308 
NATURE 
[DECEMBER 21, 1916 
exposition of the problem and his gallant attempt 
to solve it will, we hope, stimulate other biologists 
to follow in his footsteps and carry on the work 
to which his life was devoted, i.e. experimental 
embryology. E. W. M. 
OUR BOOKSHELF. 
The Heat Treatment of Tool Steel. By H. 
Brearley. Second edition. Pp. .xv+223. 
(London: Longmans, Green and Co., 1916.) 
Price ros. 6d. net. 
Tue fact that a demand has arisen for a second 
edition of this book within four years from its first 
appearance is the strongest evidence of its 
practical value. The author states in the preface 
that he is now less restrained than formerly, and 
is free to describe in greater detail the different 
methods of treating steel, and this has enabled 
him to deal with the subject much more com- 
pletely than in the first edition. 
For some time past, and especially during the 
stress of the last two years, it has been more 
fully realised than ever that the life of a tool will 
depend as much on the manner in which it is 
worked into the finished shape and on the heat 
treatment it receives as on the material from 
which it is made, and a record of the practical 
experience of the author will be of great. value to 
all directly interested in procuring the best work- 
ing results from the various steels used in the 
manufacture of tools. 
For efficient handling, the subject demands an 
adequate knowledge of the science bearing on it, 
and familiarity with the results of recent research, 
together with a wide experience in workshop 
practice. The author possesses these qualifica- 
tions to a high degree, and although the book 
deals more particularly with the practical than 
with the scientific aspect, it can be strongly re- 
commended to all interested in this important 
subject either from the practical or from the more 
purely scientific point of view. 
Alloy steels, and high-speed steels in particular, 
are more fully dealt with than was the case in the 
first edition, and the chapter on case-hardening 
has been omitted, as it has been made the subject 
of a separate volume. 
The whole subject is well handled, and the book 
can be strongly recommended as a clear and com- 
prehensive treatise on this important branch of 
technology. F. W. Harzorp. 
Laboratory Manual in General Microbiology. 
Pp. xvi+ 418. (New York: John Wiley and 
Sons, Inc.; London: Chapman and Hall, Ltd., 
1916.) Price ros. 6d. net. 
Tuis book is planned to serve as a manual of 
instruction in practical microbiology. To a large 
extent it represents the course given in this sub- 
ject at the Michigan Agricultural College, and it 
therefore “deals mostly with agricultural. micro- 
biology, and the disease-producing organisms, 
with two. or three exceptions, are omitted. 
The course is divided into 126 lessons or exer- 
NO. 2460, VoL. 98] 
cises, of which 53 are devoted to general labora- 
tory methods and to the general morphology of 
micro-organisms, 33 to the physiology of micro- 
organisms, 15 to air, water, sewage, and soil, 
11 to dairy and plant microbiology, and 14 to 
animal diseases and immunity. ov 
Each lesson is detailed under a definite plan— 
the apparatus required, the cultures necessary, 
and the method of carrying out the exercise. At 
the end of each lesson questions are asked regard- 
ing the particular results that may be obtained 
and their significance. 
The details given for each lesson are sufficiently 
full to enable the student to work independently of 
a teacher, and anyone who were to follow them 
out would possess a good practical knowledge of 
the subjects dealt with. 
Formule for stains and special culture media, 
tables of the coliform organisms, metric and other 
tables, and a list of works of reference are given 
in an appendix, and the text is illustrated with a 
number of plates and figures. : 
The work should be of considerable value as a 
laboratory handbook to both teacher and student, 
and we can cordially recommend it for this pur- 
pose. R. T. Hewretr. ¢ 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. ~ Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications.] 
Pre-Columbian Use of the Money-Cowrie in America. 
Tue letter entitled ‘Pre-Columbian Use of the 
Money-Cowrie in America,” by Mr. J. Wilfrid Jackson 
(NaturE, September 21, p. 48), offers a discouraging 
instance pf superficial reading of carefully observed 
and recorded data. 
In 1915 Mr., Clarence B. Moore unearthed, in the 
Roden Mound in northern Alabama, five cowries 
(Cypraea moneta). These shells, which came from a 
burial in the body of the mound, had been pierced for 
stringing, and showed evidence of considerable age. 
They were the only evidence found at this site of con- 
tact with the Old World (C. B. Moore, ‘ Aboriginal 
Sites on Tennessee River,’ in Journ. Acad. Nat. Sci., 
Philadelphia, second series, xvi., p. 293). In all Mr. 
Moore’s more than twenty years of most careful and 
painstaking exploration of mounds, cemeteries, and 
dwelling sites of the southern United States, from the 
Atlantic coast to Texas, and from the Ohio River to 
the Gulf of Mexico, no previous instance of the finding 
of C. moneta had been noted by him, nor has it ever 
been recorded as occurring with American pre-Colum- 
bian remains. 
of this negative evidence is that the Roden Mounds 
were, in part, early post-Columbian, and that any 
other evidence of contact they may have contained was 
of a perishable nature. To-assume, on the basis of 
this string of shells, the pre-Columbian use of the 
cowrie in America is no more justified than to claim 
for iron working a pre-Columbian age in the western 
hemisphere on the evidence of the iron celts found 
by the same Tennessee River expedition in Citico 
Mound, where absolutely nothing else Save four glass 
beads from a ‘superficial burial suggested the white 
trader and his wares. In each instance’ the presence 
The logical conclusion from the mass’ 
