In the recent past, evidence has accumulated that there is an interesting but obscure relationship between genesis of mast cells and functions of thymus (1). In the present work, the effects of removal and direct antigenic stimulation of thymus on tissue histamine and mast cell contents in various tissues were studied on albino rats. In view of the existence of blood-thymus barrier as postulated by Nossal and Mitchell (2), injections of antigen were given directly into the substance of the gland. MATERIALS AND METHODSHealthy albino rats of both sexes weighing between 120 and 150 g were used. The method of Segaloff (3) was followed for thymectomy and sham thymectomy. For thymic stimulation, injections of I , egg white in normal saline were made into the substance of thymus modifying the method of Radwon and West (4). Tissues were fixed with 10 jo aqueous formalin, processed in alcohol, embedded in paraffin and sections 5,n thick were taken for all abdominal organs and dorsal skin and 71z thick for abdominal skin and mesen tery. Tissue mast cells were stained with toluidine blue as adopted by Gupta and Skeleton (5). Tissue histamine was extracted with 10°0 trichloracetic acid as adopted by Parrat and West: (6) and assayed on terminal guinea-pig ileum. All experimental animals were sac rificed at regular intervals and the effects were observed for a period of 30 days in cases of thymectomy and for 6 weeks in cases of antigenic stimulation. Observations of tissue histamine and mast cell contents were made on dorsal and abdominal skins, liver, spleen, mesentery and kidney with mean values of four groups being recorded.

Although the blood histamine concentration during normal pregnancy is within the normal range, the serum histaminolytic power is greatly increased (1-3). This remark able increase in serum histaminolytic power is much more characteristic of pregnancy in man than in any other animals (4). The increase in serum histaminase activity starts as a rule during the second or third month, reaching a maximum in the fifth to the seventh month at which level it remains with modest variations until full term. It then rapidly returns within 3 or 4 days postpartum to the negligible values as found in normal non pregnant women (2).The placenta is very rich in histaminase activity (5) and is the principal source of in creased serum enzyme activity (6). Pathological changes in the placenta can, therefore, be expected to produce alterations in the normal pattern or sequence of changes in the serum histaminolytic power during pregnancy.Lindberg (6) recently showed that an intravenous infusion of histamine resulted in a lower concentration of histamine in blood when a woman was pregnant, and that ad ministration of aminoguanidine, an inhibitor of histaminase, to pregnant women raised the concentration of histamine in blood (7).It has been suggested that deviations from the normal pattern of increase in serum histaminase activity are indicative of an abnormal pregnancy (1), and variable changes in the enzyme activity in cases of pre-eclampsia have been reported (8). Studies on urinary excretion of histamine in cases of pre-eclampsia (9) suggest that there is increased con centration of histamine in circulation under this condition.Until recently, it has been thought that serum histaminase estimations might possibly serve to indicate indirectly the histamine content of blood, and that the high histaminolytic power of blood could thus be satisfactorily correlated with the common clinical observa tion of remission of allergic manifestations during pregnancy. Hopes were entertained of throwing light on the significance of tissue and blood histamine via studies of this factor, in the same way that studies of acetylcholinesterase have yielded valuable information on the functions of acetylcholine in the body. The reported similarities between lesions pro duced by experimental poisoning with histamine in pregnant animals and the clinico-pa thological features of pre-eclampsia and eclampsia, and the partly difect and partly in direct evidences that have accumulated pointing toward an excess of circulating histamine in pre-eclampsia and eclampsia together with the establishment of the fact that histamine produces definite hypertensive effects under certain conditions have stimulated our interest in the study of the problem of histamine metabolism in normal and toxaemic pregnancy, and have led to the hypothesis that histamine plays a decisive role in the aetiology of pre eclampsia and eclampsia, which has, hitherto, eluded discovery despite extensive research in the past six decades.It seemed desirable from the foregone facts to investigate in...

Rocha e Silva and Rosenthal (1) MATERIALS AND METHODSThe method of Rocha e Silva and Rosenthal (1) was utilized to obtain the exudates. Albino rats weighing between 120 and 150 g were anaesthetized with nembutal sodium (30 mg/kg intraperitoneally) and then 30 ml of air was injected beneath the dorsal skin to raise a pouch of 7 x 4 x 3 cm. This done of the pocket was submerged in water at 95°C for 15 to 20 sec. After scalding, the animal was suspended by its paws and 5 ml of Tyrode's solution was injected into the pouch. The animal was then shaken for 2 min after which the fluid was withdrawn by syringe and needle. The washing was repeated at regular intervals after burning and a maximum of 5 washings were done to each animal. The fluids thus obtained were mixed and injected intraperitoneally into albino rats taken in groups of ten and the percentage mortality at three different dose levels were determined during the next 24 hr. Results were taken as control readings.B.W. 501 C 67 and B.W. 204 C 67 were injected intraperitoneally in different doses one hour before administration of the exudate in a dose of 5 ml/l00 g of body weight to each rat and at least three dose levels between 0 and l00 mortality were determined for each drug.

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