8 POPULAR SCIENCE MONTHLY 



you inspect our embryological museum. We value especially a fine 

 human embryo which is in the youngest stage yet recorded by actual 

 observation in America. 



The history of staining is more definite. I have had the pleasure 

 of hearing from Professor Leo Gerlach, Sr., himself the story of the 

 introduction of coloring matters in microscopical technique. He was 

 interested about 1857 in studying blood vessels, and wishing to trace 

 them out by injection, applied to a local apothecary at Erlangen for 

 a suggestion of some red coloring matter, and the apothecary proposed 

 that he should use an ammoniacal solution of carmine, the pigment 

 extracted from the cochineal insect. Professor Gerlach employed it, 

 and in examining some of his preparations later found that the color 

 had soaked through the blood vessels into the surrounding tissues, and 

 had stained them so that they were much more distinct, and he also 

 noticed that the stain had especially affected the nuclei. He at once 

 recognized the importance of this coloration as a means of rendering 

 more clear the character of cells and tissues, and to him we owe the 

 introduction of carmine into histological technique, and it remains 

 to-day the most important and valuable coloring agent for our pur- 

 poses which we possess. The introduction of carmine marks an epoch 

 in microscopical science. It was most fortunate that the accidental 

 observation of the action of carmine was made by a man so thoroughly 

 able to appreciate its great value. Since then many other staining 

 reagents have been introduced by many different persons. I need 

 not pause now to enumerate them, or hold up your attention in order 

 to give a list of names and dates such as could be easily compiled. 

 I will only recall to your minds that the introduction of chloride of 

 gold, of osmic acid, of the aniline dyes, and of the Golgi method have 

 each of them represented the beginning of a fresh advance, which 

 without these added technical resources would undoubtedly have re- 

 mained impossible for us. 



Another class of methods are those by which we reconstruct from 

 serial sections- the anatomy of an embryo or an embryonic organ. To 

 the late Professor His, of Leipzig, we owe practically the first recogni- 

 tion of the value and possibility of such reconstruction. He employed 

 chiefly the method of drawing, by which many figures have been made. 

 The process is laborious, for each section must be drawn and then the 

 position of the parts measured and plotted off — but the labor is worth 

 while as it results in accurate representations of the anatomy of parts 

 which can not be dissected. I am in hopes that in our new Harvard 

 laboratories that this method of reconstruction from sections will be 

 applied to the adult, for I am sure that we can obtain by it representa- 

 tions of adult relations far superior to anything we now possess. 



Doubtless to many of you the method of reconstruction from sec- 

 tions in wax models is also well known and its value appreciated as a 



