494 



NATURE 



[December 15, 1921 



broadest sweep when he is least capable of 

 receiving' it. 



The 485 pages of reading matter and line draw- 

 ings give the conspectus of the animal kingdom 

 which it is hoped such a one may carry away. 

 Prof. Graham Kerr in his preface sets himself 

 three tasks : (i) To awaken and develop . . . 

 interest in biological science. (2) To lay an ade- 

 quate foundation for the superstructure of detailed 

 knowledge of the animal body. (3) To provide a 

 reasonably up-to-date account of the more impor- 

 tant animal parasites, especially of the pathogenic 

 microbes of animal origin. 



The course represented by this book is pre- 

 ponderatingly morphological. The writer holds 

 not only that our knowledge of the morphological 

 features of the lower types of animal is much 

 more advanced than our knowledge of their 

 physiology, but also that morphological study 

 affords a better intellectual discipline than physi- 

 ological : 



" The student observes structural features in 

 the laboratory . . . and he is able to compare 

 what he observes with what he is told or reads. 

 When he tries to make physiological observations 

 he finds even in the case of the simplest pheno- 

 mena that behind these phenomena are at work 

 factors, so far as he is concerned, transcendental 

 and as far beyond his powers of criticism and 

 comprehension as if they were the direct result 

 of supernatural agency." 



The only quarrel a student could have with the 

 book is one which it shares with so many scientific 

 works — that it is all so true. Few things are 

 more devastating to the unformed mind than first 

 contact with the vast mass of knowledge which 

 the ant-like industry of man has piled up through 

 the last three centuries. When the process of 

 selection is also hidden, and the innumerable 

 errors by which we have arrived at truth, the 

 student is apt to think that those who have 

 taught him so much can teach him all. His 

 faculty of scepticism, before the brute mass of all 

 this verity, lies down baffled, and his powers of 

 disbelief are not reawakened for years, or for 

 ever. The intellectual stimulus of finding a great 

 clinician out-faced and routed at a post-mortem 

 should not, even for the earliest years, be 

 neglected if in any fashion it can be reproduced 

 in zoological lecture-room or laboratory. 



Therefore, although the anatomy of the higher 

 vertebrates has been excluded from the course and 

 the mass of detail pruned vigorously, one would 

 plead for still further selection. By a glance at 

 the countless mistakes of the past the investigator 

 of the future will be encouraged. One would beg 

 the teacher, in delivering that cataract of cer- 

 NO. 2720, VOL. 108] 



tainty which batters on the head of the first-year j 

 student, to remind him not only of the rightness i 

 but of the wrongness of the theories of the past, 

 that he may pluck up heart to question those; 

 which now are current. 



The book is well printed, and the line drawings] 

 are numerous and comprehensible. For examina- 

 tion purposes the summaries ending each chapter 

 will prove of great value. The chapter on the 

 Flagellata and that on the Crossopterj'gii are of 

 special interest in view of the work done in these 

 two fields by the Glasgow school. 



The Study of Rocks. 



Petrographic Methods and Calculations , with som&l 

 Examples of Results Achieved. By Dr. A.| 

 Holmes. Pp. xix+515+4 plates. (London 

 Thomas Murby and Co., 192 1.) 31s. 6d. net. 



DR. HOLMES has produced a text-book that 

 is likely to have a far-reaching and bene- 

 ficial effect in promoting the intelligent study of| 

 rocks. Some scientific treatises are patient com- 

 pilations of the common stock of theories ant 

 facts current among specialists in the subject 

 treated. If they are at least fairly accurate ant 

 reasonably up-to-date and complete they may be 

 of great use to the student and research worker^ 

 even if they contain little or nothing that is ori- 

 ginal or novel. Others strike out a new and inde- 

 pendent line of their own, and deal only with cer- 

 tain aspects of the subject on which the author 

 feels he has a message to deliver. These, of 

 course, have a value of their own, though they 

 are not available as text-books or as works of 

 reference. 



The special characteristic of the work under 

 review is the keenness of Dr.. Holmes's outlook 

 for fresh ideas in every department of his sub- 

 ject. Sometimes he has evolved them for him- 

 self, sometimes he has added new developments 

 of his own to the methods that he has met with 

 in his unusually wide reading. He even succeeds 

 in making the w-ell-worn subject of specific gravity 

 interesting, and embodies much American work 

 that has recently been published, as well as his 

 own experience in the investigation of building 

 stones. In dealing with the procedure for the 

 separation of rock minerals, he does full justice 

 to the advances that have been made- in this 

 country in the last few^ years. His novel diagrams 

 showing at a glance the refractiv^e indices and 

 bi-refringence of minerals are remarkably success- 

 ful in giving an idea of their relations to one 

 another and the variations that occur. The chapter 

 on microchemistry should prove very useful, and 



