184
JOURNAL OF CAEMICAL EDUCATION
MARCH,1925
NEW APPLICATIONS OF BIOLOGICAL STAINS H. J. CONN, CHAIRMAN COMMISSION ON STANDARDIZATION 017 BIOLOGICAL STAINS, N. Y. EXP.STATION, GENEVA,
Dyes have certain applications which are very seldom taken into account by chemists. The textile industry uses dyes in such large quantities that their use of these products completely overshadows another very important application, namely, various laboratory applications by biologists. The amount of actual dye-stuffs used for this purpose is very small, but the use is an invaluable one, partly because of the dependence of the biologist upon dyes in much of his laboratory work and partly because dyes are used in the laboratory in connection with disease diagnosis and other matters which have an important bearing on public health. It is hard for the ordinary student of dye chemistry to realize what highly complicated procedures of delicate dyeing have been developed in the biological laboratory. This dyeing is not applied to materials in bulk but to microscopic preparations, and the colors produced are observed beneath the microscope. Objects of microscopic size and the microscopic details of tissues are all but invisible to the eye, even with the use of a high power microscope. This is because of their transparent nature and their lack of color. They can be made visible, however, by the use of the proper dyes, and in this way, biologists are able to study the minute details of nature. It is well known that dyes differ not only in their color but in the readiness with which they dye different kinds of fiber or tissue. Some dyes can be used for cotton, others for silk, while many can be used for wool but not for either cotton or silk. In the same way different microscopic objects have affinities for different groups of dyes, but the case is even more complicated when tissues are viewed under the microscope than when they are examined in bulk. Certain minute bodies within the tissue take certain dyes, others different dyes, so that it is sometimes possible by staining with the right combination of dyes to bring out three or four distinct colors visible in a microscopic preparation. All this makes the problem of biological staining a very complicated one; but to the man who is skilled in the necessary technic, it makes it possible to distinguish much more in connection with microscopic structure than if all parts of the tissue took the same dyes. The importance of this in biological research is easy to understand, but the part which biological stains play in public health is not so generally realized. A few illustrations given here will show somewhat the significance of dyes for this rather unexpected purpose. Cultures are sent to the laboratory from suspected diphtheria patients. The bacteriologist, in order to learn whether or not the culture is one of the diphtheria organism, stains with some dye, which is usually either
methylene blue or toluidine blue. If a discharge is suspected of being gonorrhoea, it is examined under the microscope after staining with a dye of the methyl violet group, mordanting with iodine, decolorizing with alcohol and then restaining with some other dye of diierent color from methyl violet. Treated in this way the bacteria in question stain with the latter dye, while the others with which they are most likely to be confused retain the methyl violet. In cases of suspected tuberculosis, fuchsin is used in staining the sample of sputum submitted, subsequently decolorizing with a mixture of acid and alcohol and restaining with methylene blue. The tubercle organism retains the red of the fuchsin, other organisms lose it and become stained with methylene blue. When it is desired to learn the number of bacteria in milk, i t is possible for the bacteriologist to make a determination by a cultural technic long in use, if a day or two is given him to allow for incubation of the cultures, but by use of the microscope i t is possible to get results in 10 or 15 minutes. In doing this the milk has to be stained with methylene blue which brings out the bacteria and leaves the background of milk almost uncolored. This determination is an important one and has many applications in connection with the sanitation of milk. Such procedures as these show how dyes are constantly being used in the bacteriological laboratory in the interests of public health. At present it is hoped, moreover, that they may have great value in' the future in the treatment of diseases as well. Medicine has long been hunting for drugs that can poison the disease germs without injuring the human body. Recent investigations seem to show that it may he possible to obtain them in numerous cases. Salvarsan (used in treating syphilis) is perhaps the best known specific drug obtained by modern research. Salvarsan happens to be a dye, and nearly all of the similar drugs recently produced are either dyes or very closely related to dyes. How this happens to be the case is not definitely explained, but i t is one more instance of the value of dyes to public health. The subject is a fascinating one and illustrations could be multiplied. This brief statement, however, is enough to show that the future will regard dyes not only as coloring matter for textiles and foods, but also as very important agents in the diagnosis and treatment of disease.
