The cecum of germfree rats, after the second week of life, enlargpi sixfold over t h a t of conventional tank-raised controls. Poor muscle tone as well as dictary factors have been incriniinatcd. We have studied the niyenteric plcxus of thcecum in conventional and germfree rats, in a n effort to find a neuronal explanatio-1 o f the plienomcnon a n d to test whether the neurovcgetative periphery is capable of adapting to the changing size.With routine and histochemical technics three salient features stood out: ( 1 ) The myenteric neurones i n the cecum of the germfree rat on a n average were three times larger Lhan those of the controls (42 ,u vs 16 p ) . Somc ncurones of the germfree cecuni attained giant size (over 130 p). ( 2 ) They showed a lower DPNH diaphorasc activity, unrelated to the increased cell siLe. ( 3 ) In the germfree r a t cecum the mcshcs of the primary fiber plexus of Auerbach h a d increased in size along thc antimesenteric border, while the network under the mesenteric attachment was smaller. The ratio betw-een the network of the two sides w a s 1:12 in the germfrcc. 1:5 in the controls.Wc have concluded that the neurones of Auerbach's plcxus i n the germfree cecum are indeed less active metabolically -a factor which m a y perpetuate the cycle of cecal distention in these animals. Thc iicurovceetative periuherv i n the cecum has shnwn itself capable to responding to the trophy .

The case of a 64-year-old white man with acquired immunodeficiency syndrome and ruptured abdominal aortic aneurysm infected with Salmonella is presented. Five points related to this case are addressed. It is feared that the vascular surgeon may face patients with acquired immunodeficiency syndrome and abdominal aortic aneurysms infected with Salmonella with increasing frequency in the future. This case raises medical, ethical, and moral questions.

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Two cases of limited infrarenal abdominal aortic dissection are reported. One patient was treated successfully with medical therapy alone, which resulted in complete resolu tion of symptoms and obliteration of the dissection. The second patient continued to have pain and eventually required aortic graft replacement. Abdominal aortic dissection may be an entity different from thoracic aortic dissection.