PHYSIOLOGY OF CYTOST ACTION 81 



the columnar liver cells. Apparently it is here that 

 coagulation of the blood takes place, for, as is clearly 

 shown in the pictures, the central vein (hepatic) is 

 entirely empty. The coagulation, or gelation, in these 

 fine capillaries prevents the free flow of blood. In 

 consequence, as more blood enters from the portal 

 vessels, a considerable pressure is exerted upon the 

 capillary walls. 



This pressure it is which brings about the distention 

 of the capillaries, and their subsequent engorgement 

 with blood. This series of events is the primary change 

 induced in the liver and is always found in fresh speci- 

 mens taken from animals in shock. A similar state of 

 affairs is found in the lung (Fig. 3) . In cases of pro- 

 found shock or in animals whose death has been in- 

 duced by the action of cytost, further changes are to 

 be noted. For example, in the section shown in fig- 

 ure 5, a definite clear area containing blood corpuscles 

 is observed surrounding the distended capillary. This 

 clear area, which has not taken the stain, is due to 

 exeresis of fluid from the capillaries. This outflow of 

 fluid, as well as the presence of blood corpuscles in 

 the clear area, is evidence of the increased perme- 

 ability of the capillaries. 



Such increased permeability has been recognized 

 by many workers in this field. Following the initial 

 work of Dale and Laidlaw ( 1919) , who observed that 

 the administration of histamine to cats caused a rapid 

 concentration of the blood cells, due to increased per- 

 meability of the capillaries, it has been assumed by 

 some that traumatic shock is due to the liberation of 

 histamine or a histamine-like substance. This point 

 will not now be elaborated upon, for as will be shown 



