The medial collateral ligament of the knee joint of mature rabbits was ruptured manually. The animals were then treated by the following 9 different methods to make a comparison of their therapeutic efficacy :
I. No treatment (control group) .
II. Immobilization in a plaster cast.
III. Immobilization in a plaster cast, preceded by a 30-min, soaking in ice water with subsequent drying while compressed with sponge rubber.
IV. Intramuscular injection of alpha-chymotrypsin, 5 ch, u., for 6 consecutive days just after rupture of the ligament.
V. Immobilization in a plaster cast and the same treatment as IV.
VI. The intraligamentous injection of corticosteroid hormone (0.05 mg Dexamethasone) just after and the 5 th day of rupture of the ligament.
VII. The intraligamentous injection of corticosteroid hormone (0.05 mg Dexamethasone) given at the 5 th and 10 th day of rupture of the ligament.
VIII. Immobilization in a plaster cast and the same treatment as VI.
IX. Immobilization in a plaster cast and the same treatment as VII.
On each animal standardized x-ray examination of the knee joint was made 3 times, i.e., before and after rupture of the ligament and before sacrificing the animal, while valgus stress (a weight of 1 kg) was applied to the knee. Observation for changes in the affected region was made at 1, 2, 3, 5 and 8 weeks.
The results obtained may be summarized as follows :
1. The rupture of the ligament was associated, on many occasions, with avulsion of the periosteum from its tibial attachment.
2. Return of forced valgus angle just before sacrificing of animal to its pre-injury level was achieved at : the 2nd week in groups III and IX; the 3 rd week in groups II, IV, V and VII ; and the 5 th week in groups I, VI and VII. It is thus apparent that results were more favorable with the use of a plaster cast than without it.
3. Macroscopical findings :
Abnormalities were less prominent and less frequent in groups without immobilization. Contracture of the knee joint was seen at the 3 rd week in groups with immobilization.
4. Histological findings :
Subperiosteal callus formation was noted at the 1st week. In groups receiving alphachymotrypsin injection (IV and V) the formation of fibrous tissue was evident at the 2nd week. The repair of fibers of the ligament was complete at the 3 rd week in groups III and IX, at the 5 th week in groups II, IV, V, VII and VIII and at the 8 th week in group. I.
5. The degree of forced valgus angle was found to be well correlated with the rapidity with which fibers of the ligament were repaired. Based on these criteria, the therapeutic procedures may be arranged in descending order of efficacy as follows :
(1) III and IX, (2) V, (3) IV and VIII, (4) II, (5) VII, (6) VI, and (7) I.

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1. Pathohistological studies were conducted on the brain especially the cerebellum of rabbits in which sodium nitrite, the methemoglobin-forming toxin, was injected in doses of 40, 60, and 80 mg/kg once daily for a short and long period.
2. Basic and permanent changes consisted of changes due to disturbance of blood circulation, such as congestion and edematous porotic changes. Degenerative changes of paren-chymatous cells were also seen.
3. The histological localization of early and characteristic injuries to the parenchymatous cells is in the ganglion cells or Purkinje cells showing degenerative atrophy or swelling imbibition, finally falling out and disappearance.
4. Degeneration, atrophy and disappearance of small granular cells in the granular layer was seen, so that this layer as the whole gives a porotic appearance.
5. Later in the course of time, degenerative changes were also seen in the molecular and medullary layer.
6. When these changes became more pronounced, the borderline between each cortical layer and between the cortical and medullary layer became indistinct. Mild degeneration of the vascular wall and perivascular edema was also noted.
7. The effect on cerebellum in the present experiment consisted of hypoxia causing disturbance in blood circulation and early degenerative changes of the parenchymatous cells through respiratory inhibition. The changes of Purkinje cells were especially pronounced, probably representing an expression of the dynamic aspect of blood distribution in relation to cells and tissues based on hypoxia and generalized circulatory disturbance. Purkinje cells in the cerebellum thus appear to become an index of hypoxic change.

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In an attempt to work up the healing mechanism of bone fracture, an experiment was conducted on young, male Wistar strain rats, 70 to 80 gm in weight, in which the animis were allocated to 4 groups according to the procedure employed for the production of fracture of the femur and the subsequetly applied orthopedic therapeutic measures ; i.e. (1) manual subcutaneous fracture without treatment, (2) osteotomy with a chisel plus intramedullary fixation with a Kirschner wire, (3) osteotomy with an electrical bone saw without concurrent application of physiological saline plus intramedullary fixation with a Kirschner wire, and (4) the same as in (3) except for the concurrent use of physiological saline, and were then observed for the bone salt deposition status at the affected site by the use of contact-microradiography, tetracycline (Achromycin^®) labelling as a tracer, ⁴⁵Ca-autoradiography (strip method) and roentogenography as well as by histologic (using haematoxylin-eosin staining) and macrosccopic examination over a period from the 4 th day up to the 6 th week after the injury. The results obtained are summarized as follows:
1) In group 1, the callus formation was initially rather poor probably and partly due to the working physical factors and became adequate toward the 3 rd week with favorable calcification as evidenced by increasing deposition of TC and ⁴⁵Ca. The excess callus tended then to be reduced gradually and complete bony union attained at the 6 th week.
2) The animals of Group 2 generally showed somewhat retarded callus formation in comparison with those of Group 1 initially. From toward the 3 rd week, deposition of TC and ⁴⁵Ca increased, calcification of the callus became prominent, but this was somewhat slower than in Group 1. Bony union was achieved in 6 weeks.
3) In Group 3, union of the broken ends was almost completely accomplished in 6 weeks, though both callus formation and uptake of TC and ⁴⁵Ca were significantly delayed initially by the action of heat generated at osteotomy.
4) In Group 4, the initial callus formation was more marked than in Group 3. At the 3 rd week ossification at the injured site was prominent with increased TC and ⁴⁵Ca uptake, diminished then gradually and resulted in bony union in 6 weeks.
5) In comparison with the bone salt deposition and histological pictures in the process of fracture healing, callus formation was most favorable in Group 1, followed by Group 2, Group 4 and Group 3 in that descending order of adequacy.
6) The fact that callus formation was markedly delayed in Group 3 (without phsiological saline) stresses the necessity of cooling the bone with physiological saline at osteotomy in actual clinical cases.
7) In young rats, as compared to mature rats, the healing of the fracture generally was quicker, in parallel with which deposition of TC and ⁴⁵Ca at the site of fracture was accomplished in a shorter period of time.
8) The present study corroborates that a combination of TC-labelling as a tracer, ⁴⁵Ca-autoradiography and microradiography provides a useful means for a close observation of the healing process of a fracture.

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