Shock and Related Phenomena 137 



gram-negative bacilli) whose active principle is mainly polysac- 

 charide or lipopolysaccharide in nature will cause shock in animals 

 if injected in suitable quantities. As in shock proper this injection 

 causes first a heightened, then a lessened responsiveness of the 

 vessels to adrenaline (Thomas, 1956; Zweifach and Thomas, 1957). 

 Unlike shock, however, endotoxin causes hypertonicity of venules. 

 Nevertheless, rats and rabbits rendered tolerant to endotoxin by 

 repeated injection are thereby protected from shock due to haemor- 

 rhage or trauma (Zweifach et al. } 1957) . Moreover, the blood of 

 shocked animals including those suffering from acute haemorrhage 

 where infection is an unlikely complication contains a substance 

 with many of the properties of bacterial endotoxin (Smiddy and 

 Fine, 1958; Schweinberg et al., 1957) . 



It is known that prolonged hypotension delays the clearance of 

 bacteria from the circulation (Schweinburg et al., 1954) . It is also 

 known that in shock, circulation through the intestine is very poor 

 and that devitalisation of the bowel wall is likely to occur, with in- 

 creased likelihood of the passage of bacteria and bacterial products 

 into the circulation. In fact, in some circumstances, shock may be 

 prevented by perfusing the intestine of injured animals with arterial 

 blood (Lillehei, 1956) . Furthermore, not only do shocked animals 

 exhibit reduced levels of endogenous bacteriostatics, e.g. Properdin, 

 (Frank et al., 1955) , but they are in addition hypersensitive to the 

 effects of injected endotoxin and bacteria (Schweinburg and Fine, 

 1955) . Moreover, resistance to shock induced by repeated small 

 traumatic stimuli may be overcome by infection. Finally, it was 

 found, and confirmed in many different species and circumstances, 

 that oral antibiotics, including some compounds not absorbed 

 from the bowel, protected against shock due to trauma or haemor- 

 rhage (Frank et ah, 1952) . 



However, not all the evidence favours the view that endotoxin 

 is a major factor in shock. Thus although shocked animals are hy- 

 persensitive to endotoxin, guinea pigs rendered sensitive to endo- 

 toxin by other means are not hypersensitive to shock. Conversely, 

 rats rendered resistant to shock by injection of yeast extract or de- 

 natured albumin are not resistant to endotoxin (Zweifach, 1958). 



