;40 



NATURE 



\_At/£2^s/ 1 1, ibS; 



inscription on British soil corresponds to the Scandina- 

 vian formula by which, " from analogy," Prof. Stephens 

 would read those found, but unfortunately not given, by 

 Sir Herbert Maxwell. JOSEPH LuCAS. 



0[/Ji BOOK SHELF. 



The Prevention of Co7tsumption. By C. Candler, Mel- 

 bourne, Victoria. (London : Kegan Paul and Co., 

 1887.) 

 This may be considered a book of theories. The author 

 promises by " his theory " to revolutionize the treatment 

 of phthisis, and almost to bring the disease to an end 

 among civilized nations. 



The theory is briefly stated thus : " Ordinary phthisis is 

 invariably caused by a local bacillary malaria governed 

 by chemical light." When the author speaks of bacillary 

 malaria, he means that the tubercle Bacillus is like a 

 saprophyte, capable of growing and thriving in the soil, 

 and that from the soil, which is its true birthplace and 

 home, the Bacillus or its spores find entrance into 

 the human system : fortunately for humanity solar light 

 destroys many of these Bacilli. 



" It will be observed," says the author, on page 191, 

 " that it is presupposed that the consumptive, and they 

 who are sickening with consumption, are, or have recently 

 been, exposed to a bacillary malaria fostered by an in- 

 sufficiency of solar radiation, and this is one of the 

 inferences which urgently requires to be verified." Quite 

 so ; and this the author ought to have done himself, 

 though he hopes that somebody else will furnish the 

 proof. 



The prevention of phthisis the author has no doubt of 

 achieving by plenty of sunlight ; and he would force the 

 Governments to supply more sunlight to the inhabitants 

 of big cities, where, as is known, consumption is rife. It 

 is a pity the author does not tell us how this is to be 

 achieved in London or Manchester during a great part 

 of the year. E. Klein. 



Metal Plate Work : Its Patterns and their Geometry. 

 By C. T. Millis. (London : E. and F. Spon, 1887.) 



This work is one of the series of Finsbury Technical 

 Manuals, and teaches how all ordinary patterns required 

 by sheet metal-workers can be set out on one geometric 

 principle. It is the first work in which the setting out of 

 such patterns has been systematized. The manufac- 

 ture of every article in common use is treated as a 

 separate problem, but the principle in all cases is that 

 the parts composing it shall be set out mathematically, 

 so that any worker having become accustomed to cut 

 out his work on this principle could equally apply it 

 to new forms. The first chapters are of the most ele- 

 mentary character, so that the work is not necessarily 

 above the head of ordinary mechanics. That the book 

 is an admirable manual there can be no question, 

 but whether such a book will be widely consulted ap- 

 pears doubtful. In the opinion of two of the chief tin- 

 plate workers in Birmingham the knowledge it imparts 

 will save time and prevent waste of material, which results 

 when the rule of thumb and guess-work are in vogue, 

 whilst the workman using it will gain confidence, and his 

 value be increased by the certainty of his pattern working 

 out true. Nevertheless, the great mass of workmen in 

 metals are not yet educated up to the use of such a work, 

 and in all probabihty in a centre like Birmingham it 

 will only fall into the hands of managers of manufactur- 

 ing establishments and a limited number of first-class 

 workmen. It is a book, however, that must be required 

 by the artisan more and more to meet the rapid strides 

 of education, and it will, we hope, command a satisfactory 

 sale. 



Walks in the Ardennes. Edited by Percy Lindley. 

 (London: W. H. Smith and Son, 1887.) 



This hand-book, which only costs sixpence, contains all 

 the information the ordinary tourist is likely to want in 

 walking in the Ardennes. The writer is verv familiar 

 with the country, and describes clearly and simply the 

 various routes and the chief centres of interest. There 

 are a sketch map of the Ardennes, and a good many 

 illustrations. 



LETTERS TO THE EDITOR. 



\The Editor does not hold hitnself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 tcike to return, or to correspond with the writers oj\ 

 rejected manuscripts. No notice is taken of anonymous 

 com m unications. 



[ The Editor urgently requests correspondents to keep their 

 letters as short as possible. The pressure on his space 

 is so great that it is impossible otherwise to insure the 

 appearance even of cotnmunications containing interesting 

 and novel facts. '\ 



The Parietal Eye in Fishes. 



In my short paper on this subject which appeared in Nature 

 of July 14 (p. 246) there are one or two points which need better 

 elucidation than I then gave them. 



In the first place, for the sake of brevity, my reference to 

 Ahlborn's valuable paper is too scanty, and I am unwilling to do 

 any injustice to that excellent observer. 1 did not believe 

 he had ever really been fortunate enough to get sections of the 

 " pineal gland " of a fully adult Petromyzon planeri ; for, judging 

 from what I had found in every adult examined, I imagined 

 that had he possessed fully adult Petromyzon he must have 

 noticed the black pigment in the parietal eye, and moreover must 

 also have seen and figured the deep fossa in the skull {vide 

 my figure in Nature, p. 247), in which, in the adult, the 

 parietal eye rests. It appeared as though his descriptions and 

 figures of the adult brain had been taken from specimens in 

 which the metamorphosis was not quite complete. I have again 

 studied his figures, and must admit that in other respects some 

 of his drawings represent the brain of adult Petromyzon. The 

 apparent contradiction seemed strange, but it is fortunately not 

 inexplicable. 



I mu?t here mention that Petromyzon planeri is no longer 

 here in Freiburg so plentiful as when Calberia worked on it, now 

 more than ten years ago. Indeed, I have had great difficulty in 

 obtaining adult and very young specimens. The older Ammo- 

 coetes, though not common, are not so rare. 



This being the case, I could not examine the number of 

 individuals I should have otherwise wished to do. However, I 

 have now found one adult Petromyzon in which there was, no black 

 pigment in the parietal eye and no fossa for the eye in the skull. 

 That the specimen was otherwise adult is certain. This find 

 accounts for the non-discovery by other observers of the black 

 pigment I have described. The parietal eye in Petromyzon, 

 which is a rudimentary organ, like many other rudimentary 

 organs is probably also variable in different individuals, and it 

 is not impossible that the black pigment of the parietal eye is 

 entirely absent in the Petromyzon found in many places. 



So far as I can judge at present — and I intend to further 

 examine the point — the parietal eye in the Blindworm {Anguis 

 fragilis) is also variable. It certainly varies in size and in 

 distinct ess. 



The second point relates to the black pigment, Wiedersheim ^ 

 and Ahlborn have stated that the pineal gland in Ammocoetes ' 

 possesses a gray-white pigment. Owing to scarcity of living 

 Ammocoetes I have not verified this, but I do not for a moment 

 doubt it, and I did not mention it, firstly because I did not 

 think it important, and secondly because I did not wish to ' 

 lengthen the paper. 



1 did not describe the pigment in the adult as black, but that| 

 such was the case could be inferred from the description, and in j 

 not stating its colour I was only following an excellent authority, 

 Prof. Carri^re, who, in his book " Die Sehorgane der Thiere," ! 

 in many cases does not state the colour of eye-pigments. One! 

 usually assumes that a retinal pigment is black. 



