4. =Thymus.= The writer believes that the weights usually given for the thymus in the new-born are too high, and that 7-10 grms. represents the usual normal weight. A gland weighing 20 grms. or more must be regarded as enlarged. The organ reaches its fullest development at the end of the second year. Atrophy begins then, developing slowly up to the age of puberty, after that more rapidly. In adults the thymus normally consists of a mass of adipose tissue containing lymphoid nodules, in some of which corpuscles of Hassall persist to old age. Postmortem softening should not be mistaken for abscesses. The most important pathologic change is hypertrophy. Pressure of the enlarged gland upon the trachea, nerves or great vessels may cause thymic stridor, asthma, or thymic death (“lymphatic constitution”). Enlargement of the thymus may occur in “status lymphaticus,” exophthalmic goitre, cretinism, myxœdema, Addison’s disease, acromegaly, myasthenia gravis, epilepsy, scorbutus, rachitis, tonsillar hyperplasia, adenoids, congenital syphilis, Hodgkin’s disease, leukæmia, anencephaly, anæmia, acute infections, or it may exist as an independent affection. Oedema, congestion, inflammation, tuberculosis, neoplasms, etc., may also cause an enlargement. Absence of the thymus has been observed. Primary and secondary forms of atrophy in association with marasmus occur in children. Note relation of size of thymus to condition of child; atrophy of the organ is usually coincident with marasmus. Inflammation, tuberculosis, cysts, primary and secondary neoplasms, gummata, etc., are not common.