NATURE 



73 



THURSDAY, MAY 2S, 1896. 



THE PHOTOGRAPHY OF HISTOLOGICAL 

 EVIDENCE. 

 An Atlas of the Fertilisation and Karyokinesis of the 

 O'l'uni. By E. B. Wilson, with the co-operation of 

 E. Learning-. (New York and London : Macmillan, 

 1895.) 



PROF. WILSON has earned the :.4ratitude of teachers 

 and students of biology by publishing his "Atlas 

 of Fertilisation." He has collected, on ten plates of a 

 convenient size, a series of photographs illustrating the 

 development of Toxopncustcs, from the mature ovarian 

 ovum until the formation of a si.xteen-celled blastosphere. 

 The photographs were made by Dr. Learning, from 

 sections prepared by Prof Wilson ; and they have been 

 admirably printed from untouched negatives. Each 

 figure is about three and a half inches in diameter, so that 

 all details capable of photographic reproduction can be 

 easily seen. 



The first plate contains two photographs of ovarian 

 eggs, in which the nuclear stnicture is well seen ; a third, 

 showing the nuclear division leading to the first polar 

 body ; and a fourth, showing the mature egg after 

 extrusion of both polar bodies. The next four plates 

 illustrate the entrance of the spcrmatozobn, the ap- 

 proximation of the male and female nuclei, and the 

 formation of the " asters." The sixth plate shows the 

 changes in the approximated nuclei during the pause 

 which follows the entrance of the spermatozoon ; and the 

 seventh, eighth and ninth contain twelve very beautiful 

 figures of the first division of the fertilised cg^. Finally, 

 some of the later divisions are exhibited on the tenth 

 plate. 



The photographs are accompanied by a short but clear 

 account of the phenomena they are intended to illustrate ; 

 and in many cases difficult details are rendered intelligible 

 by means of diagrams. 



There can be no doubt that this Atlas will be of great 

 ser\'ice to students and to teachers, as an exposition of 

 our present knowledge concerning the main facts of 

 fertilisation ; although one is tempted to regret the 

 absence of any figures demonstrating the number of 

 chromosomes, either in the polar bodies or the pronuclei. 

 The excellence of the work suggests, however, another 

 standard by which to judge it — a standard indicated by 

 Prof. Wilson himself in his preface, when he points out 

 that the most careful drawings involve a subjective 

 element from which photographs are free, and states his 

 belief that, in spite of certain necessary shortcomings, 

 " the photographic plates here presented give, on the 

 whole, a clear and accurate impression of the pre- 

 parations." 



If photography could indeed pro\ide an image of his- 

 tological preparations, as clear and accurate as that 

 received by the eye of a trained observer, then a great 

 step would have been made ; for every histologist would 

 be enabled to convey to others the whole evidence for 

 his statements in a way before impossible ; and a photo- 

 graph, when once successfully taken, might serve as 

 NO. 1387, VOL. 54] 



material for future research in the hands of men unable 

 to procure the object photographed. 



Unfortunately, Dr. Leaming's photographs, admirable 

 as they are, do not approach the perfection necessary 

 if they are to be regarded as representing the whole 

 evidence given by the actual sections. This may easily 

 be seen by any one who tries to determine from them the 

 truth of some statements made in the text. 



Prof Wilson holds the view, now shared by the 

 majority of observers, that both the centrospheres of 

 the fertilised eg^ arise from a portion of the spermato- 

 zoon ; and he considers that the male and female 

 chromatin elements lie side by side, without mixing, 

 during the division of the single original centrosphere. 

 As evidence of this, he gives photographs 17, 18 and 19, 

 and woodcuts xi. and xii. In the woodcuts, the distinc- 

 tion between the male nucleus and the female is clear 

 and unmistakable ; while, at least in photographs 18 and 

 19, this is not the case. Again, in the photograph fig. 

 19 there is no clear indication of structure in the male 

 nucleus ; while in the woodcut fig. xii. B, which may 

 well have been drawn from the actual section photo- 

 graphed, a distinct reticulum is indicated in its substance. 



Few persons will believe that Prof Wilson has made 

 positive statements on the evidence of sections showing 

 no more than the photographs referred to : every one 

 will feel that the woodcuts represent the essentials of 

 his preparations better than the photographs. So that 

 we have to judge the question, after all, by reading the 

 authoi-'s account of what he says he saw ; and when 

 photography has done its best, the evidence of the con- 

 dition of these nuclei at a particular moment still rests 

 upon his reputation as a histologist, as completely as 

 it would have done had he published the woodcuts only, 

 or no figures at all. 



In the case just referred to, the author's statement is 

 so completely in accord with those of other workers, 

 that few will hesitate to accept it ; but when he points to 

 photograph No. 19 as evidence that the rays of the 

 amphi-aster " are really fibres, and not, as some recent 

 authors have maintained, merely the optical sections of 

 thin plates or lamelte in a radially arranged alveolar 

 structure," there is equally little evidence one way or the 

 other to be obtained from the photograph, while there is 

 more room for doubt as to the accuracy of the inter- 

 pretation. The reference is, of course, to Biitschli's 

 work on the structure of protoplasm ; and those readers 

 of Nature who have compared Prof Biitschli's photo- 

 graphs with his drawings, will remember that in his case 

 also the photographic reproduction of the evidence was 

 not a material addition to the strength of the argument. 



On the whole, it seems certain that the best photograph 

 at present possible does not show so much as can be seen 

 by looking directly at a good histological preparation : so 

 that it is not yet possible for a histologist to multiply 

 copies of his evidence in a form from which the subjec- 

 tive element is altogether excluded. There is still no 

 way of testing a histological statement without direct 

 examination of the object described. Further, it seems 

 that a careful drawing by a trained observer gives a better 

 idea of appearances seen under the microscope than the 

 best available reproduction by photography can at present 

 achieve. W. F. R. Weldon. 



