March 8, 1894] 



NATURE 



431 



are decidedly more simple. Here again we find Messrs. 

 Crossley Bros, to the fore with an engine designed on the 

 lines of their Otto gas engine, and certainly working 

 economically and without trouble. 



Part iii. deals with air engines, a subject which has 

 occupied the minds of engineers for many years, and 

 one which appears to baffle their best designs and 

 schemes. These motors deal with low working pressures, 

 and are necessarily bulky for their power. In the Ericsson 

 engine, for instance, the pressure was only 3 lbs. per 

 square inch. 



The author says in the preface that, "in both oil and 

 gas engines, about 40 per cent, of all the heat received 

 now goes off in the exhaust gases, and about 35 per cent, 

 in the jacket water." This is nothing new, and the 

 remedy lies in the better expansion of the heated gases. 

 This with the Crossley engine is difficult, but with Prof. 

 Rowden's engine very complete expansion is obtained, 

 and consequently a low pressure at exhaust and a far 

 cooler cylinder. Of course this end is obtained by 

 sacrificing simplicity of design and working parts ; at 

 the same time it is questionable whether it would not be 

 worth while experimenting in this direction, considering 

 the great saving to be obtained by more complete ex- 

 pansion. The question of compounding gas engines has 

 not been overlooked, more than one having been con- 

 structed ; but difficulties have arisen in connection with 

 the valves, and these have only partly been overcome. 

 The difficulty of making a valve to continually pass hot 

 gases is enormous. Yet this is evidently the direction 

 in which economy is to be found, and its solution is 

 merely a question of time. 



Another point of importance in the economy of the 

 gas engine is the question of accuracy of manufacture ; a 

 badly made gas engine is sure to be a constant trouble, 

 and as many now on the market are bad copies of the 

 Crossley engine without its accuracy and finish, one is not 

 surprised to occasionally hear of failures of this class of 

 motor. 



This volume contains a very complete and accurate 

 record of all that has hitherto been done in the design of 

 internal combustion motors. The information has been 

 well brought together, and the illustrations are excep- 

 tionally good. The author is to be congratulated on the 

 completion of an excellent book on a subject very little 

 understood by general engineers. N. J. Lockyer. 



PHYSIOLOGY FOR SCIENCE SCHOOLS. 

 Human Physiology. By John Thornton, M.A. (Lon- 

 don : Longmans, Green and Co., 1894.) 

 ' I "HE book before us belongs to a class which requires 

 J- some apology for its existence. This particular 

 work has been prepared for lay students intending to 

 present themselves for the second or advanced stage of 

 the Science and Art Department. It aims at being 

 something more than a mere cram book, and in justifi- 

 cation of this aim it professes '• to furnish precise and 

 accurate information on such parts of histology and 

 anatomy as are required, as well as to give a reasoned 

 account of the physiological processes of the human 

 body." For all this, however, the book belongs to a class 

 NO. 1 271, VOL. 4q] 



to which e.xception may justly be taken. The writer 

 appears to have depended almost entirely upon the exist- 

 ence of descriptive physiological works for his material. 

 The result is that the book represents simply a compila- 

 tion of physiological facts, and in no sense can it be 

 described as a guide to physiological practice. The 

 South Kensington examinations, both elementary and 

 advanced, attempt, as far as their opportunities permit, 

 to test the practical acquaintance of a candidate with the 

 subject in which he presents himself for examination. 

 This is very frequently found to be non-existent, and most 

 usually the reason of this is that the teacher himself is not 

 in a position to act as an instructor in the practical work 

 of a subject he professes to teach. There exists a large 

 number of books which give the minimum of the required 

 amount of physiological fact necessary to impart to his 

 pupils, and upon these alone he usually depends. This 

 class of books gives the teacher no information as to the 

 best way to demonstrate practically the facts he teaches, 

 for the reason generally that the writers themselves are 

 unacquainted with the methods. These books are the 

 class which we would wish to see abolished from our 

 elementary science schools ; they are necessarily un- 

 reliable, and they always tempt the teacher who uses them 

 to depend upon a wholly artificial knowledge of little 

 practical value whatever. What advantage is it to a 

 student to know that if fibrin be " placed in gastric juice 

 and the mixture kept at a temperature of about 40^ C. . . . 

 in about an hour the fibrin will be in great part dis- 

 solved " .^ By itself this is simply a naked fact (though 

 stated in the way the writer puts it, it can hardly be 

 called a fact). The whole process could be shown the 

 student in the most simple way on the lecture table, and 

 unless he actually sees the change produced by the gastric 

 juice, he can, as a rule, have but an imperfect idea of 

 what really occurs. 



All these books that aim at being guides to elementary 

 science teaching should have so much simple instruction 

 as to the methods to be adopted to actually show the 

 different processes described, as can be done, having re- 

 gard to the opportunities of an elementary science 

 school. In physiology a very considerable knowledge 

 can be imparted simply by demonstration, and to ignore 

 this and depend simply upon oral description is to teach 

 physiology in a way that, we are glad to say, is rapidly 

 becoming obsolete. If this volume were supplemented 

 with practical demonstration, it might serve a useful pur- 

 pose. But the divorce from practical acquaintance with 

 the subject is frequently emphasised. In referring to 

 coagulation, the writer says that " by adding to plasma 

 about 14 per cent, of a saturated solution of sodium 

 chloride a white flaky sticky precipitate of fibrinogen is 

 thrown down." The author intends to be precise, but 

 there is a considerable difference between the statement 

 above and the actual fact, viz. that solid sodium chloride 

 should be added so that it becomes dissolved to the ex- 

 tent of 14 per cent. Later, in treating of the absorption 

 of food, the author commits himself to the following 

 statement : " We know of a physical process called 

 filtration, by which is meant the passage of fluids through 

 the pores of a membrane under pressure. Substances 

 that may be obtained in the form of crystals, or 



