A positive control is included in each kit for the purpose of checking the effectiveness of the reagents.
FUNGUS (PL. FUNGI)
Fungi are heterotrophic, chlorophyll-free, thallophyllic organisms. They reproduce by spores, which germinate into long filaments called hyphae. As the hyphae continue to grow and branch, they develop into a mat of growth called the mycelium (pl. mycelia). From the mycelium, spores are produced in characteristic arrangements. These spores, when dispersed to new substances, germinate and form new growths. Reproduction is often asexual, usually by budding, as in yeast, but certain fungi have sexual reproduction.
Common superficial infections of the skin caused by fungi are athlete’s foot and ringworm of the scalp.
POTASSIUM HYDROXIDE (KOH) PREPARATION FOR IDENTIFICATION OF FUNGI
Fungi are seen in clustered round buds with thick walls accompanied by fragments of mycelia. Scrapings from the affected area of the skin are mounted in 10 percent KOH for positive laboratory diagnosis.
Demonstration of the fungi in infected tissue can be accomplished by the following method:
1. Place skin, hair, or nail scrapings from the affected area on a slide and add a drop of 10 percent KOH. Dissolve 10 g of KOH in 100 ml of distilled water.
2. Place a coverslip on the preparation.
3. Warm the preparation gently over a flame, being careful not to boil it, and allow it to stand until clear. Do not allow the preparation to dry out.
4. Read preparation, using a high-power objective with subdued light.
a. Fungi in the skin and nails appear as refractive fragments of hyphae.
b. In the hair, fungi appear as dense clouds around the hair stub or as linear rows inside the hair shaft.
BLOOD GROUPING
Blood transfusion, the term used for the process of transferring blood from one person to another, is often a lifesaving remedy, especially in cases of severe hemorrhage, anemia, and infection.
In 1900 Landsteiner discovered the first blood group system that initially comprised groups A, B, and O. Later the AB system was added.
AGGLUTINATION
The work showing that blood can be classified into these four groups was done by random cross matching of the bloods of a large number of people. Two specific antigens (also called agglutinogens) were found on the red cells. These were called A and B. One group of red cells contained no A or B antigen and was called O. A fourth group contained both A and B antigens and was called AB. Antibodies (agglutinins) were found in the serum of blood. These were called anti-A and anti-B antibodies. A person of group A blood (A antigen) has anti-B antibodies (agglutinins) in the serum. A group B individual has anti-A antibodies; a group O individual has both anti-A and anti-B antibodies; and group AB individuals have neither antibody in the serum. With the exception of certain patients with autoimmune diseases, individuals do not have antibodies against their own blood type.
Landsteiner’s rule states that when an antigen is on a red blood cell, the corresponding antibody is never present simultaneously. Instead, the reciprocal red cell antigen is present in the plasma or serum. For example, if an individual has blood cells of group A, anti-B antibodies are always present in the serum but never anti-A.
Blood grouping is accomplished by comparing the effects of agglutination by the antibodies on the corresponding antigens within the red cells.
To determine the group to which blood belongs, it is necessary to mix separately a suspension of its red cells with serum of a known group A and a group B that contains agglutinin B and agglutinin A, respectively. The resulting agglutination or absence of agglutination determines the group to which it belongs and is a necessary procedure with the blood of both the donor and the recipient. Only compatible blood is selected for transfusion. One of the four