ARTICLES 279 



sure therein is the view most generally accepted as the first 

 stage of the production of urine. 



But there is another way in which increased exudation 

 from capillaries may be brought about. Suppose that the 

 walls become permeable, not only to salts, but also to colloids. 

 There is then no osmotic force to oppose nitration, because the 

 osmotic pressure of the proteins cannot be effective. Now, 

 such an effect is produced by histamine and other products 

 of tissue destruction. If it has reached a high value by pro- 

 longed action of the toxic substance, it cannot be restored to 

 normal. Accordingly, in late and severe stages of wound 

 shock, neither blood nor intravenous gum-saline is effective. 

 The liquid escapes from the blood-vessels in a comparatively 

 short time and the blood-pressure falls to its former low level. 

 The occurrence of this condition is shown by the coincidence 

 of a low blood-pressure with a high haemoglobin content of the 

 blood, indicating loss of fluid, whereas normally the low pres- 

 sure would be associated with dilution. This latter was, in 

 fact, recognised as a favourable sign. If the change in permea- 

 bility has not become too great, the introduction of blood or 

 gum-saline may restore the normal state (see N. M. Keith). 



A similar action to that of histamine on the permeability 

 of the capillaries appears to be exerted by prolonged deficiency 

 of blood-supply, probably owing to want of oxygen. The low 

 pressure of shock in itself exaggerates the direct effect of the 

 tissue toxins. 



t In certain regions of the body, such as the liver, and to 

 some extent the intestines, the capillaries are normally more 

 permeable to proteins than in other regions, and lymph is 

 accordingly more abundantly formed in such regions. It also 

 contains a certain amount of protein. But, of course, the 

 pressure in the portal vein is much lower than that in the 

 arteries, and the lymph produced also ultimately finds its way 

 back into the blood. 



LITERATURE 



W. M. Bayliss, Intravenous Injection in Wound Shock, Longmans, 1919. 



„ „ , Vaso-dilator Fibres and their Nature, Journ. Physiol., 26, 173, 



1901. 

 W. M. Bayliss and W. B. Cannon, Traumatic Toxaemia as a Factor in Shock- 



Special Report, No. 26, Med. Res. Committee, 19 19, 19. 

 H. H. Dale and P. P. Laidlaw, The Physiological Action of Histamine, Jturn. 



•f Physiol., 41, 318, 1910. 



