Brookfield Zoo, Brookfield, Illinois, has been exceptionally cooperative and generous with the collection of hairs from an array of animals at their zoo.  Several samples were examined and “A Microscopical Study Of Exotic Animal Hairs: Part 1” was just the beginning of what could become lifelong work. Working with the zoo has enabled McCrone Associates to begin setting an exhibit in the Hamill Family Play Zoo, located within the Zoo, to teach guests how hairs appear when viewed through a microscope. This, hopefully, will allow younger generations to begin to appreciate the capabilities of the microscope. The exhibit will be interactive, displaying a flip-book picturing reference samples, set next to microscopes used to view the samples. The collection of hairs provided has made it possible for McCrone Associates to take transmitted-light photomicrographs using plane-polarized light, fully-crossed polarizers, and scanning electron micrographs (SEMs), and make scale castings of the actual hairs.

In this follow-up to “A Microscopical Study Of Exotic Animal Hairs: Part 1”, the animals have been chosen at random. The Brown Bear, Western Lowland Gorilla, and African Wild Dog are all on the endangered species list. The Zoo is an active participant in the Species Survival Plan (SSP) for both the Western Lowland Gorilla and the African Wild Dog. The California Sea Lion, due to its protection by the Marine Mammal Protection Act of 1972, is not considered endangered. The Aardwolf is currently classified as rare. 

Brown Bear (Ursus arctos)

Ursus arctos, commonly known as the Brown Bear, is found on three continents, making it the most widespread bear species on Earth. Although its range is wide, its population numbers are still low. Brown Bears have been hunted, and their habitats have been overtaken by human expansion, which may explain why they are on the endangered species list. Their body color is usually dark brown, but can range in shades from a cream-color to almost black. Some of their hairs may be tipped with a whitish-silver color giving their coat a sheen-like appearance.

In Meltmount™ 1.662, you will notice a continuous medulla in both transmitted light and with fully-crossed polarizers. This sample has a stellate appearance, finger-like projections radiating out into the cortex; this type is often found in the tail hairs of larger mammals. Figures 1 and 2 are X300 photomicrographs of Brown Bear hair (both polarizer and analyzer have been rotated 45°).

click image to enlarge (256K) Figure 1

click image to enlarge (260K) Figure 2

Notice the moderately high birefringence using fully-crossed polarizers (Figure 2). You can just begin to make out the scale pattern along the edge of the hair in the transmitted light photomicrograph (Figure 1). The photomicrograph of the cross-section, Figure 3, shows a circular-to-oval shape with a transparent medulla due to the stellate appearance. The medullary index was calculated to be 0.14.

click image to enlarge (329K) Figure 3

Scale casts were made of the hairs using clear nail polish in order to provide optimum study preparation of the scale pattern. The contrast and definition are both greatly improved (Figure 4); the irregular mosaic scale pattern is now easily visible. Images were captured at X1200, 10 kV, using a scanning electron microscope (SEM), to show more topographical detail which is visible at this higher magnification. This sample is ~64 µm wide, and has 8-12 scales per 100 µm. The margins appear to be relatively smooth and near to one another (Figure 5). 

click image to enlarge (132K) Figure 4

click image to enlarge (228K) Figure 5