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The microscope is one of the most valuable tools a rehabilitator can own. While detection of some pathogens (disease-causing organisms) may require the skill of a veterinarian or technician, others can be done on site without invasive procedures or complicated equipment. Fecal samples or oral swabs can be examined for internal parasites, yeast and/or or bacteria.

A microscope is likely to be most useful in detecting parasites, including 'worms' and protozoa. Every newly admitted animal should be checked and treated for external and internal parasites before being introduced to other animals. Because the animal may not pass parasites or eggs every hour of every day, a single fecal sample may not reveal anything. A series of tests throughout the day or week may be necessary. There are a number of good texts or websites that offer images of parasites and eggs at different stages of development listed in the parasitology section of this site.

Identification of bacteria is necessary so that the appropriate antibiotic can be chosen, but requires more steps than does identification of parasites. A specimen is placed on a glass slide. After it has dried, it is dyed or stained so that that the organisms are easier to see.

Dr. Hans Christian Joachim Gram devised a method now known as 'Gram's Stain'. First, bacteria are stained with gentian violet (a dye). Then, they are treated with Gram's solution (a mixture of water, iodine and potassium iodide). Then, bacteria are washed with ethyl alcohol. After washing, they are either colourless, or retain the blue colour of the dye. Another stain (e.g. eosin or fuchsine) is sometimes applied to give the colourless bacteria a reddish cast to make them visible.

Bacteria that retain the blue stain are gram-positive. Bacteria that are not blue are gram-negative.

Antibiotics can sometimes be chosen based on the shape and gram staining characteristics of bacteria. However, many bacteria are normal denizens of the mouth or feces, so thorough knowledge of clinical microbiology is a necessity. In addition, antibiotic resistance of formerly sensitive kinds of bacteria often makes culture for sensitivity a requirement of good clinical practice.

To learn how to use a microscope, prepare samples or where to order reconditioned equipment, choose one of the topics below.