OUTGROWTH OF THE NERVE FIBER 
807 
is believed that any deviations which may have crept in have 
not misrepresented the essential character of the structures. The 
original sketches were made only in outline. The finished draw- 
ings, which are reproduced in the plates, were traced from these, 
details of texture being filled in in accordance with studies made 
for the purpose. Individual cells, when appearing by themselves, 
have been in most cases drawn in with the camera, but in indi- 
cating the larger masses of cells nothing more has been attempted 
than to give their general character. For instance, the exact 
arrangement of yolk and pigment granules was not copied because 
it was felt that this was not essential, and it would have required 
much time to the exclusion of the study of essential features. 
Study of the material has been confined almost entirely to the 
fresh preparations. In fact it must be admitted that one serious 
defect in the work has been the impossibility of obtaining satis- 
factory preserved specimens. The ideal procedure would be first 
to study the growth of a particular fiber, recording the events by 
frequent sketches, and then to preserve that same specimen, dem- 
onstrating by suitable histological methods the structural iden- 
tity between the fibers studied and the nerves found within the 
embryo.^" Owing to the extreme delicacy of the structures and 
to the almost fluid consistency of the lymph drops, it has, however, 
been impossible to do this, since the mere immersion of the prep- 
aration in any fluid brings about a disarrangement of the tissue, 
and in many cases the clot with the implanted tissue becomes 
loosened from the cover, or the tissue falls out of the clot. The 
method which has given the greatest promise is fixation in osmic 
acid vapor with subsequent hardening in Tellyesniczky's bichro- 
mate acetic mixture, and staining in alcohoUc haematoxylin by 
the method of Oskar Schultze '04. In some of these preparations 
1" Since this was written Dr. M. T. Burrows of the Rockefeller Institute, while 
working with me has devised a satisfactory method for obtaining permanent 
preparations. He has shown that embryonic nervous tissue of the chick, when 
isolated in the proper medium, gives rise to the same long filamentous proc- 
cesses as does that of the frog; and further, that by staining the preparations in 
Held's molybdenum haematoxylin the neurofibrillae in these filaments are brought 
out very clearly. An account of this work will be published at an early date. 
