696 
in future editions. The statement that the action of 
these hormones is catalytic is unjustified and means 
nothing. We cannot speak of catalysis—i.e. a hastening 
of a chemical action—unless we have some definite 
chemical action in mind. In the case of these hormones, 
as in the case of drugs such as alkaloids, we have not 
the remotest idea how they work. It may be that their 
action is by catalysis of one or other of the reactions 
which occur in the series making up the life of the cell, 
but there is no evidence for or against such a statement, 
and there is a distinct danger that, by putting the 
action of drugs or hormones into such a category, we may 
forget our ignorance and refrain from further attempts 
at an analysis of the manner in which they work. 
The author seems unaware of the fact so clearly 
brought out by Pézard, that the plumage of the cock is 
that of the neutral animal, desexualisation of the hen 
bringing about the production of the cock’s plumage, 
which is left unaffected in the male by removal of the 
testes. It is not correct to speak of enterokinase as a 
hormone ; it is a ferment which has a definite action 
on the trypsinogen secreted by the pancreas, converting 
this into trypsin. Two statements are a little surpris- 
ing. In explanation of the term “ thyroidectomy ” it is 
mentioned that “‘ dectomy ” equals excision. Later on 
in the book the word “ secretin ”’ is stated to be derived 
from the Greek “‘ to excite.” These,.however, are minor 
flaws and do not interfere with the value of the book as 
a whole, which can be recommended as an interesting 
and well-balanced account of the present condition of 
our knowledge on the subject of internal secretions. 
It is couched in such language that it will be intelligible 
to any educated reader with the veriest smattering of 
scientific knowledge. FE, (ES .3: 

Modern Processes of Ore-Dressing. 
A Text-Book of Ore-Dressing. By Prof. S. J. Truscott. 
Pp. xi+680. (London: Macmillan and Co., Ltd., 
1923.) 40s. net. 
N his preface Prof. Truscott states that his work is | 
written primarily for the service ofhis ownstudents 
at the Royal School of Mines, and correctly observes 
that such a book is needed owing to the important 
development of flotation processes in recent years. 
From the dedication—“ To Almighty God, the father 
of our Lord Jesus Christ”—one must infer that the 
author has put forth his best efforts into the work, 
and it certainly does bear evidence throughout of pains- 
taking care. The matter is arranged methodically ; the 
drawings and diagrams are abundant and excellent, 
and their selection leaves little to be desired. The 
many non-essential details which are often found in 
NATURE 


[May 26, 1923 
the space is well employed to give the student a correct 
and easy understanding of the subjects described. 
The book deals first with washing and sorting 
methods and appliances, then with the various types of 
machines for breaking, crushing} and grinding of ores. 
Next are considered the problems and appliances for 
sizing by screens and by water, after which water con- 
centration is described. The latter half of the book — 
deals mainly with flotation concentration, magnetic, 
electrostatic, pneumatic, and centrifugal separations. 
The space devoted to flotation (one-fifth of the total 
text) is indicative of the rapid growth and extreme 
practical importance of this method of concentration, 
which in less than twenty years has revolutionised the 
treatment of low-grade ores. 
On the whole, the author is to be congratulated upon . 
his presentation of a concise view of flotation technics 
to the general student, since the subject matter is 
extensive and in some aspects recondite. Under these 
conditions his treatment of the practical section must 
be considered satisfactory, but the chapter devoted to 
the more theoretical aspects of the subject is somewhat 
involved. This is scarcely to be wondered at, since a 
comprehensive theory of flotation (which at almost 
every point involves problems in regions of molecular 
physics only partially explored) has yet to gain general 
acceptance, and is still the battle-ground of two schools 
of thought—those on one hand who adopt the doctrines 
of the later school of ccllcid chemists, seeking explana- 
tions for causation based mainly on electrical theories, 
and the other or physical school, which finds sufficient 
explanation by the application of purely molecular 
laws. Electrical theories are both proximate, as the 
assumed electrical or electrostatic nature of flocculation 
and deflocculation phenomena, and ultimate, in seeking 
to explain the useful properties of oils and other re- 
agents used in flotation in terms of the electronic 
constitution of atoms and molecules. The physical 
school is concerned only with the elucidation and 
quantification of the molecular attractive forces exerted 
between the reacting surfaces at liquid-solid contacts, 
such as give rise to surface- and interfacial-tensions, 
adsorption, and so on. On these grounds the pheno- 
mena of flocculation and deflocculation also seem to be 
more satisfactorily explained than by the electrical 
hypothesis. 
Prof. Truscott, however, prefers to divide his favours 
between the two schools, accepting molecular attrac- 
tions as explanatory of most of the flotation reactions, 
but adopting the electrical hypothesis for flocculation. 
The importance of the latter factor may be judged from 
the generalisation, now widely accepted, that where 
particles in an ore-pulp can be flocculated they can be 
descriptions of ore-dressing plants do not occur, and all | floated; conversely, when they are put into the 
NO. 2795, VOL. 111] 
