214 Caroline McGill, 



cut in serial sections. From about a length of 45 mm up, the portions 

 of the alimentary canal needed were dissected out and embedded 

 separately. The sections were cut from 3 micra to 10 micra in 

 thickness. The microscopic lenses used were the following: Leitz 

 ^/^2 in. oil immersion objective; Bausch and Lomb ^|-^Q in. oil immersion 

 objective; and Zeiss 2 mm 1 : 30 apochromatic, with compensating 

 oculars. 



The material was stained in various ways. For all general pur- 

 poses, as well as for differentiating the myofibrillae, Heidenhain's iron- 

 haematoxylin with a counterstain of eosin or Congo-red was found to 

 give excellent results. With this method, by staining and decolorizing 

 for various lengths of time, different effects may be produced. More- 

 over, structures which are not shown by the ordinary method, may 

 be demonstrated by repeated immersion in the haematoxylin followed, 

 in each case, by extraction in the iron-alum. When deeply stained 

 in the haematoxylin and not far extracted, all of the smooth muscle 

 fibrillae may appear as coarse fibrillae, a mass action of the stain 

 being obtained. When extracted further, the coarse fibrillae still retain 

 the haematoxylin, but the finer ones are decolorized and stain with 

 the protoplasmic stain. Extraction may be carried to such an extent 

 that only the chromatin of the nucleus stains black with the haema- 

 toxylin, all the myofibrillae taking the protoplasmic stain. Muscle 

 fibrillae have a tendency to stain much more intensely with ordinary 

 oxyphile stains, such as eosin and Congo-red, than do the collagenous 

 (white or reticular) fibrillae of connective tissue, this being one means 

 of differentiating them from collagenous fibers. Iron-haematoxylin, 

 when the tissues are left in the haematoxylin for a long time, 24 hours 

 or more, stains the elastic fibers, as well as the myofibrillae, black, so 

 that it is sometimes difficult to differentiate them. Next to iron- 

 haematoxylin, Delafield's haematoxylin was found best for bringing 

 out the general structure of smooth muscle. 



To differentiate collagenous fibers, Mallory's anilin-blue connective 

 tissue stain gives the most satisfactory results. However, with this 

 stain in the younger embryos it is often impossible to distinguish 

 developing myofibrillae from white or reticular fibrillae. With this 



