1. The defence mechanisms of the body are predominantly functions of the reticulo-endothelial system (RES). Stimulation of the RES leads to increased body defence indicated by increased phagocytic activity, raised serum \g=g\-globulin and increased protection of experimental animals against virulent infections. The strongest RES stimulants appear to be oestrogens, natural and synthetic.2. In the mouse, 0\m=.\002 mg. diethylstilboestrol daily is sufficient to produce significant prolongation of survival time against infection.3. RES activity varies at different stages of the oestrous cycle and of pregnancy in both the rat and the mouse. The stages where the activity is greatest correspond with those in the human subject when the output of oestrogens is increased.4. The results suggest that oestrogen is the natural stimulant of body defence in both the male and female, the latter having high oestrogen levels when protection against infection is normally most needed. 5. RES stimulation does not rise in step with oestrogenicity, and oestrogenic compounds have two separate biological activities\p=m-\onewhich stimulates the RES to raise body defence, and one which acts on the reproductive organs; these two activities are apparently unrelated, although shared by the same molecule.

The administration of morphine was followed in white mice by a typical Straub reaction which consisted of the tail becoming rigid and erected across the back of the animal in an S-shaped curve. This reaction was accompanied by restlessness, excitability, extension rigidity of the hindlimbs, forcible viodance of faeces and prominence of the perineum. The Straub reaction was abolished by general anaesthesia with pentobarbitone or ether, by administration of tubocurarine, by bilateral section of the muscles causing extension to the tail, and by the removal of the circulation to the lower extremity. The reaction was modified by unilateral section of the extensor muscles of the tail. Section of the spinal cord, decortication, division of the anal sphincter and perineal floor, or ablation of the pelvic splanchnic nerves did not suppress the appearance of the Straub response. It was concluded that the phenomenon described by Straub (1911) was produced mainly by the action of the sacro-coccygeus dorsalis muscle, and that it was also necessary that the lumbo-sacral cord with its peripheral nervous outflow should be intact and that these functioning units should have an adequate circulation. Straub (1911) described the sensitive biological reaction for morphine which bears his name. He stated that " when white mice are injected with a small quantity of morphine under the skin of the back, their tails go into a condition of catatonic rigidity which is manifested in such a way that, during the strongest dorsiflexion, the tail is in a position almost parallel to the vertebral column." Subsequent investigators have confirmed and extended these observations. Herrmann (1912) called attention to restlessness, reflex excitability, extension paralysis of the hindquarters, lordosis of the vertebral column and an S-shaped curve of the tail. Van Leersum (1918) reported that defaecation occurred soon after the injection of morphine and that the perineum became prominent. The explanations for the phenomenon found in current textbooks of pharmacology show some disregard for anatomical and functional considerations, particularly in connexion with the skeletal and visceral musculature involved. Gaddum (1955) states that "morphine has a peculiar effect on mice, making them hold their tails erect owing to spasm of the anal and vesical sphincters," and similar explanations are given by *Present address:

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