In situ hybridization (ISH) performed after different time spans of prolonged formalin fixation. Positive cells are labeled dark purple. a-c, lymph node, pig. ISH for Porcine circovirus-
2: 1 week (a); 8 weeks (b); 10 weeks (c). d-f, lung, pig. ISH for Porcine respiratory and
reproductive syndrome virus: 1 week (d); 10 weeks (e); 29 weeks (f). g-i, stomach, snake. ISH for Cryptosporidium serpentis: 1 week (g); 48 weeks (h); 62 weeks (i). j-l, colon, pig. ISH for Tritrichomonas sp.: 1 week (j); 47 weeks (k); 62 weeks (l). Bar = 400 μm.