26 



Methods and Techniques 



scope to examine the blastoderm of the chick. 

 Alchemy and pharmacology had puzzled 

 over the uses of specific salts, at least since 

 the ninth centuiy, for the adult organism; 

 the modern statement of the fundamental 

 chemical problems of embryology awaited 

 the nineteenth century. If the embryo waited 

 centuries for even such simple quantitative 

 approach as had been devoted to the adult by 

 Sanctorius Sanctorius, it had to wait millen- 

 nia, from the time surgeons first used their 

 scalpels on biological material to cut off an 

 offending member, for the hot needle of Roux 

 and the discerning eye of Chun (1880) who 

 observed comparable effects of the stormy 

 Mediterranean seas. John Hunter had at- 

 tempted modern methods of grafting in the 

 adult organism over a century before trans- 

 plantation techniques were applied to em- 

 bryological material. There is surely no 

 simple reason to account for these long de- 

 lays in embryological evolution. But cer- 

 tainly they may be related to the fact that 

 no method or technique developed for other 

 sciences, even within the biological realm, 

 has been adequate to enable the embryologist 

 to come to grips with his fundamental and 

 most inescapable problem, the nature of em- 

 bryonic organization. 



The important progress, then, in the his- 

 tory of embryology, has been in the gradual 

 changes in the cast of thought and clarifica- 

 tion, as it seems from our point of view, in 

 the setting of the question to be answered 

 by the embryo. How the question is ex- 

 pressed, at any one moment in history, is of 

 course conditioned by the technical proce- 

 dures available at the time, as well as by 

 the influence of more general currents of 

 thought; and the problem of the embryolo- 

 gist becomes the problem of asking a ques- 

 tion, with whatever means are at his dis- 

 posal, that the embryo can answer in a 

 manner intelligible to the investigator. 



What are the means of investigation avail- 

 able to the embryologist today? How have 

 they developed? To what degree do they per- 

 mit adequate reply to the problems they 

 purport to attack? What are their limitations 

 and how far can these be overcome? In what 

 measure do they inhibit, as did the late 

 nineteenth century concentration on genea- 

 logical research, or in what way do they en- 

 courage, as did the happy exploitation of 

 the transplantation method by Spemann and 

 Harrison, the posing of new and searching 

 problems? What does the experience of the 

 past and the present inform us at all usefully 

 as to how the future might best be explored 



in terms of new techniques and of new prob- 

 lems? These are questions which the em- 

 bryologist must answer if he is to review his 

 work in proper perspective with relation to 

 larger fields, and only by so doing can he 

 hope to facilitate his approach to the prob- 

 lems next facing him. 



OBSERVATION VS. INTERFERENCE AS AN 



APPROACH TO EMBRYOLOGICAL 



PROBLEMS 



Modern embryology, since Roux, has 

 tended strongly both in its pedagogical and 

 investigational aspects to contrast the de- 

 scriptive, or morphological, or observational, 

 approach, with the so-called experimental, 

 an only apparent distinction whose illusion 

 of dichotomy leads to an important paradox 

 to be taken up below. But since the observa- 

 tional method, at least in a crude form, has 

 always been available to the investigator, a 

 few of the difficulties inherent in the inter- 

 pretation of what seem to be the simplest ob- 

 servations may be pointed out at the begin- 

 ning of this discussion. Since even the results 

 of experiments must be observed in some 

 fashion, and this is only part of the paradox, 

 these difGculties of interpretation are of sig- 

 nificance in a much wider sense and there- 

 fore will be discussed also in relation to the 

 broader issues. 



In the first place, observation of the em- 

 bryo can rarely, if ever, remain observation 

 pure and simple. This seems a truism; yet 

 there are certain inferences to be drawn from 

 it which are not so completely obvious as it 

 might seem. 



Perhaps the greatest interference with con- 

 structive and advancing observation derives 

 from the preconceptions already present in 

 the mind of the observer, and there is no 

 need further to labor the point that modern 

 investigators, like the great minds of the 

 past, like Wolff, like Roux, tend to see in 

 terms of what they are looking for. 



It is the what-he-is-looking-for that is so 

 strongly conditioned by the mechanical tools 

 at the disposal of the embryologist, which 

 both expand and limit what is visible to him. 

 In the early days of the microscope the em- 

 bryologist saw organs, tissues, layers, per- 

 haps cells. With the improvement of the 

 techniques of microtomy and staining and 

 with the perfection of achromatic lenses he 

 could examine parts of the nucleus and what 

 now seem the grosser cytoplasmic inclusions. 

 The technique of modern optics and micros- 

 copy enable him to push his frontiers far 

 beyond the old limits, and new instruments 



