the density of gold particles , expressed per micron2 , was negligible in controls ( less than or equal to 1.1 ) , but averaged 307 , 146 , and 23 , respectively , for laminin , collagen iv , and proteoglycan over the thick basement membranes ( except for descemet 's membranes , over which the density was 16 , 5 , and 34 , respectively ) and 117 , 72 , and 64 , respectively , over the lamina densa of the thin basement membranes .
C0009333
collagen iv
C0004799
basement membranes