Page:Popular Science Monthly Volume 69.djvu/12

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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 purposes 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 remained 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 recognition 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 representations of adult relations far superior to anything we now possess.

Doubtless to many of you the method of reconstruction from sections in wax models is also well known and its value appreciated as a