Abstract
During recent attempts to cultivate B. leprae in embryonic chick tissues, 1 an interesting observation was made on the close morphological resemblance of this microorganism in freshly excised human leprous tissue to the rod shaped pigment of the chick retina. This observation is considered worthy of note because of the possibility of confusing these bacilli and pigment rods when employing embryonic tissue as a culture medium. Furthermore, as Rivers 2 points out, the presence of the pigment rods may lead to confusion when smears are made to determine the sterility of the cultures. For this reason, he suggests removing the eyes of the embryo before making use of the tissue as a medium. We, however, prefer to include as much of the highly specialized tissues as possible and, therefore,. make use of the entire embryo.
The rod-shaped pigments are found within the inner surface of the hexagonal epithelial cells of the retina, this layer being considered the outer layer of the optic cup. They occur normally in tightly packed masses and usually with regularity. However, their arrangement can be readily disturbed by mechanical means; that is, the packets are easily broken by ordinary manipulation and their component rods are freely scattered when embryos are either minced or sectioned. When this dispersion occurs, these pigment rods and packets can be mistaken morphologically for those of B. leprae and the “globi” found in human leprous tissue. The individual pigment rods are 1–5μ in length, dark brown in color and resistant to the penetration of dyes. The distribution of the pigment within the rods is usually homogeneous, but sometimes it is irregular and simulates the chromatin “beading” so characteristic of acid-fast bacilli.
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