Abstract
The development of the lyssa was studied consecutively on each life stadium of dogs, all selected from those of common hybrid type close to the Japanese species. These were sacrificed at every five days interval from 20th embryonic day to 15th postnatal day of the animal's life. By 28th embryonic day, the lyssa starts developing at the tip of the tongue as a mass of interstitial cells generally arranged in concentric direction, extending itself backward approximately 1.35mm. By 30th embryonic day, it increases to 2.72mm in antero-posterior length. The transversal sections of the anterior and posterior parts resemble to the sections from 28th day specimens. However, the sections at the center part shows the presence of a mass of irregularly arranged young parenchymal cells surrounded by a mass of young circumscribing cells. By 35th embryonic day, it reaches approximately 3.80mm in length, and two or three layers of cells outside of the circumscribing cell group are already differentiated into connective tissue serving as a sheath. By 40th embryonic day, it reaches approximately 4.61mm in length, and the inner part of the circumscribing cell group and the outer part of the parenchymal cell group already turn into a muscle substance engirdling the remaining parenchymal cells inside. By 45th embryonic day, it reaches approximately 5.79mm in length, the parenchymal cell group being already differentiated into a longitudinal muscle. The stage of life from 50th embryonic day to 10th postnatal day of the animal is marked by increase of the bulk of the lyssa which is now approximately 6.27 to 8.70mm in length. The growth is particularly accentuated by elongation and full growth of the posterior part of the lyssa where marked development and increase in both the circumscribing and longitudinal muscles are observable. By 15th postnatal day, it reaches approximately 7.84mm in length and all the tissue elements including the adipose tissue which comes last to develop at the anterior and posterior parts of the body and between fibers of the longitudinal muscle, proceed toward their final development to complete the embodiment of the lyssa.
