or the other of which sources is recommended to anyone desiring a 

 more detailed account than is given here. 



Besides the fairly common application of iodine to microscopic 

 preparations there seems to have been no further effort to color 

 objects under the microscope until the middle of the century. At 

 this time carmin was used almost simultaneously by two botanists, 

 Coppert and Cohn (1849) and by a zoologist Corti (1851). Goppert 

 and Cohn used the dye to assist them in studying the rotation of 

 the cell contents of Nitella flexilis. Corti's work is overlooked by 

 both Gierke and by Mann; but he states definitely (p. 143) that to 

 observe distinctly the epithelial cells one should color them lightly 

 with a solution of sugar or of carmin in a mixture of half water and 

 half alcohol. This work was very promptly followed by another 

 use of the same dye — the staining of chlorophyl granules in plants 

 — by Hartig (1854 and 1858). In studying the nucleus of cells he 

 made use not only of carmin but of litmus and black ink; and he 

 observed that while albumin and gelatin were easily stained, the 

 dyes had no action on such material as gums and mucin. Altho 

 these authors did careful scientific work and certainly were the first 

 users of dyes for histological purposes, their work apparently at- 

 tracted no attention at the time. The real introduction of bio- 

 logical stains was made by Gerlach (1858). 



Altho Gerlach did not discover the action of dyes on microscopic 

 objects, nor was he the first to use carmin, nevertheless he should 

 be, and generally is, considered the father of the technic of staining. 

 Having observed that tissues became colored after injection with a 

 poorly prepared carmin gelatin, he devised the scheme of preparing 

 an ammoniacal carmin. He was therefore the first to use ammon- 

 ium carminate, which is so nearly indispensible to modern histolo- 

 gists. His early efforts with it, however, were unsuccessful — until 

 he had a lucky accident which revealed the source of his trouble 

 and opened up the way for further work. He happened to leave a 

 section of nervous tissue, which had been hardened in potassium 

 bichromate, over night in a very dilute carmin solution. When he 

 examined it twenty -four hours later he found that it was beauti- 

 fully stained, with fine differentiation of nerve fibers and nerve 

 cells. His earlier failures had been due to the use of too strong a 

 solution of the dye. This gave the key which helped solve the 

 problem of tissue staining. Advances came quickly after that; for 

 Gerlach had shown the way, and others merely had to follow. 



These advances were not wholly with carmin; altho at first the 

 anilin dyes were scarcely kno"v\-n and the number of stains available 

 to microscopists was quite limited. Indigo was first employed by 

 Maschke (1859) who was familiar with Hartig's work but not with 

 Gerlach's. It is stated (anonymous, 1865) that Thiersch and 

 Miiller had just developed a technic employing carminates in com- 

 bination with oxalic acid, and a year later Schweigger-Seidel and 



8 



