Histochemical examination of the middle ear muscles of cats and rabbits was carried out to investigate the difference among muscle fibers composing them and the correlation between the function and the structure of individual muscle fibers.
The muscle was frozen and sectioned about 25 -30μ thick. For the histochemical demonstration of lipid, succinic dehydrogenase, cytochrome oxidase, and DPN-diaphorase, the methods established by Lison, Wachstein et Meisel, Gräff, and Farber et al were applied respectively.
The results obtained were as follows.
(1) It was revealed that the tensor tympani and stapedius of cats and rabbits are composea of the fiber giving a high enzymatic activity of succinic dehydrogenase, cytochrome oxidase and DPN-diaphorase and showing an intense affinity to Sudan black B and the fiber giving very slight reaction of them. The former may correspond to red or dark fiber and the latter to w hite or light fiber. Besides these, there exists a third type of muscle fiber in the stapedius, which shows a moderate enzymatic activity and is intermediate between the red and white muscle fibers.
(2) Generally, the white fiber showed a tendency to be thick, while the red fiber to be thin. In the tensor tympani the distribution ratio of the red and white fibers, which markedly varied individually, was approximately 3: 2 or 1: 1. In the stapedius the distribution ratio of the red, white and intermediate fibers was approximately 3: 2: 1 or 2: 2: 1.
(3) It is inferred that these three types of muscle fibers which are different trom eacn other in enzymatic activity as well as in the number of mitochondria vary in respiratory activity and metabolic process and accordingly have different physiological functions specific to each type. It is supposed that the red muscle fibers participate in tonic contraction, while the white muscle fibers participate in phasic movement. Muscle fibers of the intermediate type are supposed to have similar function to that of red fibers, judging from their enzymatic activity.(4) Concerning the function of the middle ear muscles, it is p resumed that the red muscle fibers take part in the maintenance and adjustment of specific functional condition of the sound conduction system by giving continuously active tonus to the ossicular chain, while the white muscle fibers participate in rapid contraction in case of middle ear muscle reflexes.

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An enormous amount of research has been reported on the acoustic trauma since the experimental study of this trauma was initiated approximately half a century ago. However, some of its pathogenesis, course and general characteristics have not been clearly elucidated as yet. The reversibility of the acoustic trauma is one of the problems still remain unsolved. In the present experiment, the acoustic trauma of Corti's organ of guinea pigs was induced by exposin g the animals to a white noise of 115 phons, 8 hours per day, for a few days. The traumatized inner ears of guinea pigs without receiving any treatment has been daily observed in comparison with those of the animals treated with various drugs. By this mean the author intended to throw some light on the susceptibility of the guinea pig's inner ear to the acoustic trauma and the reversibility of the traumatic changes being so induced. The results obtained will be summarized as follows:
1. No recognizable change appeared in the Corti's organ of guinea pigs exposed to the noise for one day, while the exposure for 3 days resulted in a definite change. This is apparently due to the resistivity of the animal's organ against the acoustic load.
2. The acoustic trauma induced in this way could be divided into two types showing different courses. In one type (A), the traumatic change was fixative or showed a slight improve ment as the time advanced. Namely, the resulted change did not progress further and was somewhat reversible. On the other hand, in the other type (B), the traumatic change was progressive and Corti's organ usually showed a marked atrophy or sometimes it disappeared eventually.
3. Drugs given to the guinea pigs showing the type A change accelerate the healing of the pathological changes of the inner ear, while those given to those of type B slightly retarded the progress of the degenerative change or had no effect at all.
4. Traumatic changes of the inner ear showed a conside rable difference from animal to animal in spite of the acoustic load was given under the same condition. It would be extremely difficult to investigate the cause, but the diversity may be regarded as the individual d ifference in the intrinsic facter of each animal.

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The following are the findings obtained in reference to the study conducted on the effect of over-dose, and deficiency of vitamin-A on the histological changes of the ear, nose, pharynx, larynx, and trachea, utilizing mouse as experimental animal:
1. Thicknes of the mucous membrane: The over-dose of vitamin-A had caused the membrane to atrophy, and the deficiency had caused to hypertrophy. In regard to the pars olfactoria of the nasal mucous membrane, and the hypopharynx, no cignificant changes were recognized in the group with over-dose of vitamin-A.
2. Cornification of skin and mucous membrane: The skin of the external auditory meatus was recognized to have the tendency to cornificate in both groups, the over-dose and the deficiency groups, and this tendency was noticed to be greater in the latter group.
Further, it was also recognized that the mucous membrane of the pharynx have a greater tendency to cornificate in the deficiency group than that of the over-dose group.
3. Changes in the glandular cells
a). Height of the glandular cells: The glandular cells under the mucous membrane of the nasal septum, supraglottic region of the larynx, were recognized to atrophy in the over-dose group, and many hypertrophied cells were recognized in the deficiency group.
b). The amount of glandular cells: The amount of glandular cells under the mucous membrane of the nasal septum, supraglottic region of the larynx, and the larynx were recognized to have the tendency to decrease in the over-dose group, but contrarily, increase in the deficiency group.
4. Height of cilia and papillae on the mucous membrane: The height of the cilia on the mucous membrane of the tympanic cavity and the nasal septum have the tendency to shorten in the over-dose group, and the taller cilia have the tendency to increase in the deficiency group.
The papilae on the epipharynx mucous membrane have the tendency to shorten exceedingly in the over-dose group, but almost no change is recognized in the deficiency group.
5. Changes in the cartilage: In regard to the thickness of the cartilage in the nasal septum, no change was recognized in both groups. Further, a tendency to ossificate was recognized in the thyroid cartilage of the external auditory meatus, nasal septum, in both groups, but the ossifica-tion was noticed to be more cignificant in the deficiency group, particularly, a greater change was recognized in the thyroid cartilage of the nasal septum.
6. Osseous changes: In regard to the osseous change of the bony portion of the external auditory meatus, the auditoryossicles, and the bony labyrinth, an excessive sediment of lime is produced in both groups, and this symptom is more significant in the deficiency group.
7. Thyro-arytenoid muscle: A trace which seemed that both internal and the external of the thyro-arytenoid muscles had emaciated and atrophied was recognized in the over-dose group, and many traces were recognized in the deficiency group which can be considered to have hypertrophied.
8. Soft tissues of the external auditory meatus: An emaciation of the soft tissues and their atrophy wererecognized in the over-dose groups and on the contrary, hypertrophy were noticed in the deficiency group.
9. Nasalturbinates: the tendency to atrophy and the tendency to hypertrophy were similarly recognized in the recognized in the over-dose and deficiency groups.

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