The present study dealt with the influence of isolated hemoglobin upon the histochemical peroxidase reaction, and also with the application of this staining method to tissue sections. The materials used include cartilage, skin with hair, and mucosa of alimentary tract of 17 different vertebrates from mammal to fish, and benzidine and orthophenylenediamine were used for the substrates of peroxidase reaction. This new technique, called the indirect peroxidase reaction, is characterized by treating tissues with very dilute hemoglobin solution before the tissue is stained with peroxidase reagent.
It was revealed here that the interstitial substance of cartilage and the stratum germinativum of stratified squamous epithelium are intensely stained with the indirect peroxidase reaction, suggesting that the hemoglobin molecule is able to intensify the ordinary peroxidase reaction, and that the indirect peroxidase reaction is related to the basophilia of tissue, and perhaps as well to the proliferative activity of cells.
The prin c iple of the indirect peroxidase reaction is thought to be adsorption of hemoglobin molecules to a definite region of cell or tissue which causes a pseudoperoxidase reaction in various degrees.
Evidence was therefore presented that the animal p igment, hemoglobin, is applicable to tissue staining because of its high pseudoperoxidative activity.

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A total of 121 pregnant m ice were used for this study. Quantitative histometrical measurements (frequencies per square millimeter of occurrence of follicles over 50 it in diameter and irregular-shaped follicles, and percentages per field of occurrence of follicles containing darkly stained colloid) were made. It was found that some histological fluctuations may occur in follicles and colloid with the progress of gestation.
Early pregnancy: Immediatly after mating the thyroid gland is composed predominantly of small follicles and colloid is feebly stained. During the first half of this period the gland is composed of large follicles with a predominant occurrence of darkly stained colloid and suggests a transitory storage phase. During the second half, presumably shortly before and at the time of implantation of fertilized ova, the gland shows a trend to decrease in size and irregular change in shape of follicles, together with poorer staining of colloid, marked swelling of follicle epithelium and capillary hyperemia.This may suggest evidently a phase of release of colloid.
Mid pregnancy: The gland shows a trend towa r d s increase in size of follicles and subsequently a stable state of follicles and colloid. The gland is generally composed of large follicles with darkly stained colloid.
Late pregnancy: The gland indicates a slightly unstable state, especially near term. Colloid stains inconstantly. General follicles are decreased in size and show irregular change in shape.
The author wishes to acknowledge his thanks to Prof. D r. Shooichi Sugiyama for his kind guidance throughout the course of this study. Further, the author is indebted to Prof. Dr. C hikataro Togari for kind encouragement and help.

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A total of 249 primiparous mice were used for histological studies of the thyroid gland of mice in relation to lactation, weaning and the sexual cycle. The animals were divided into two groups of lactation and weaning. The lactation group consisted of mother mice who nursed 4 sucklings up to 25 days after parturition and weaned at the 26th day. The weaning group consisted of mother mice who were forced to wean immediately after parturition.In both groups, the vaginal smear test was made on mice who weaned their sucklings.
In the lactation group-Immediately after parturition, the thyroid gland shows a microfollicular trend, feeble staining and much vacuolation of colloid and swelling of follicle epithelium with increased formation of secretory droplets. Subsequently, the gland indicates almost the same state until weaning. Immediately after weaning, the gland shows for awhile a transient increase in size of follicles (macrofollicular trend), and swelling of follicle epithelium with newly increased formation of secretory droplets.
In the weaning groupThe thyroid gland s hows a finding similar to that found in the early period of the lactation group. The formation of secretory droplets in the follicle epithelium, however, is less frequent. From 17 days after parturition, the gland shows for a while a transient increase in size of follicles and swelling of the follicle epithelium with increased formation of secretory droplets.
The thyroid gland shows histologically no significant changes in relation to the sexual cycle. The gland, however, shows on the average a slight decrease in size of follicles in diestrus, and a slight decrease in staining of colloid in estrus and metestrus.

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A total of 165 japanese human fetuses were used in this study, and certain phases of glandular activity in prenated life were histologically elucidated. The thyroid development is divisible into the following three categories: (1) early differentiation stage, (2) preparatory differentiation stage, and (3) follicle stage.
The early differentiation stage (until 13 mm CRL,7 weeks) includes the following. In 3 to 5 mm the thyroid primordium appears as a globular solid body with a stalk arising from the pharyngeal floor lying between the first pair of visceral pouches. Separated from the floor in the 6 mm stage, it descends ventrocaudad growing into various forms such as a plate, globule and bibbed structure, which contain a few intraprimordial cavities, and finally changes into an arch-like structure in the 13 mm stage. During this stage primordial epithelial cells are immature and arranged in conglomerates, and cords, bands and plates of two cell thickness. The nuclei are vesicular and of various sizes.
The cytoplasm is sparsely granular and contains glycogen. The preparatory differentiation stage is divided into three parts: The first part (14 to 31 mm CRL,8 to 10 weeks) includes the increased formation of cell cords, bands and plates, the second (32 to 48 mm CRL,10 to 11 weeks) the increased formation of primitive and transitional follicles, and the third (50 mm CRL to 90 mm CHL,11 to 12 weeks) the production of half-mature colloid in transitional follicles. The substance is faintly stained with eosin and red purple by periodic acid-Schiff's method. The epithelial cells are still immature and contain glycogen.
At the 95 mm CHL stage (12 to 13 weeks) the follicle stage begins by the increasing formation of definitive follicles with typical colloid, at which stage capillaries forming plexus around the fo llicles occur in abundance. The colloid is moderately eosinophilic and periodic acid-Schiff positive. Most of the follicles connect with each other directly by their epithelial walls, and form follicular networks without forming a branching tubular system of exocrine glandular pattern. The epithelial cells become the follicle cells and come to contain no glycogen. The follicle cells contain often periodic acid-Schiff positive secretory droplets. Some of them are transformed into colloid cells, whose cytoplasm is intensely positive to the same reaction,
The author wishes to acknowledge his sincere thanks to Prof. Dr. Shooichi Sugiyama for his kind guidance throughout the course of this study. Further, the author is indebted to Prof. Dr. Chikataro Togari for kind encouragement and help.

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