PATTERNS OF THE A-V PATHWAYS 



909 



fig. 12. Superficial vascular pattern, temporal quadrant, 

 right eye. [From Grafflin & Corddry (56).] 



may be considered to contain all the blood vessels in 

 the areas under observation. While the walls of capil- 

 laries were never seen and their detection is dependent 

 on the presence of blood in the vessels, it is unlikely 

 that the same vessels would be devoid of blood con- 

 sistently over a period of months during which re- 

 peated observations were made. 



Vasomotion was a prominent feature of flow in the 

 vessels of this mucous membrane. It was indicated by 

 variations in the speed of flow, alterations in the 

 caliber of individual vessels, and intermittent blood 

 flow through capillary vessels. Arterial vessels usually 



fig. 13. Superficial vascular pattern, nasal quadrant, right 

 eye. [From Grafflin & Corddry (56).] 



had a rapid and continuous flow. At times the 

 arterial vessels showed irregular alterations in the 

 rate of flow, a reduction in the speed occurring some- 

 times gradually, sometimes abruptly, and sometimes 

 stopping completely for a brief interval before surging 

 forward. 



Concerning small arteriovenous communications, 

 there are three criteria to distinguish them from 

 true capillaries: /) a larger caliber than capillaries, 

 2) vasomotion, 3) continuous flow at variable speeds. 

 However, one or all of these criteria might be un- 

 satisfied on occasion. Grafflin & Corddry (56) were 

 unable to detect precapillary sphincters at the points 

 of emergence of true capillaries from the arteriovenous 

 channels. It may be assumed that this failure was due 

 to the limitations of the technique, in that the walls of 

 the small vessels were not seen distinctly. 



Venous flow is described as being continuous at a 

 relatively moderate speed with irregular alterations 

 in flow. At times the flow stopped completely. This 

 does not concur with the description given by Lee & 

 Holze (77), who reported venous flow as consistently- 

 regular. 



Bloch (15), in a lengthy article dealing primarily 

 with red cell aggregates, describes arterioles and 

 venules in the bulbar conjunctiva in the following 

 way: Arterioles in the bulbar conjunctiva do not 

 differ from arterioles in other tissues. As elsewhere, 



