Lumbar nerve 8341 Cornual nerve 422 Tongue 117211 Lips andgingiv 44 Soft palate 55 Esophagus 11 Rumen 3111 Abomasum 11 Small intestine 211 Skin 20218 Muzzle 3111 Penile sheath 541 Eyelid 33 Cartilage

The BPV used in this study originated from five natural cases (Isolates 293, 306, 307, 310, 312) and one experimental case (Isolate 3 11) of cutaneous bovine fibropapillomatosis. These warts were typical, mature fibropapillomas that were surgically removed and stored in a frozen state or kept at 4°Cin 50% glycerin. The histologic details from light and electron micro scopic studies of these warts have been previously described (14). The procedure for extracting virus was essentially similar for each isolate. The epithelium, in which BPV replicates (13), was dissected from the thawed or glycerinated fibropapillomas and partially homogenized (Virtis homogenizer, Virtis Co., Gard ner, N.Y.) at 4°C for 1S minutes using saline or 1 M NaCl 0.01 M Na2PO4 to make a 10-20% suspension. Some suspen sions were subjected to tryptic (0.01%) digestion overnight and the pH adjusted to alkaline (pH 8). Further homogenation was done with a Polytron homogenizer (Brinkmann Instru ments, Westbury, N.Y.) at 4°Cfor 1 minute. The tissue sus pensions were clarified by centrifugation at 7,700 and 37,000 x g for 20 minutes, and the supernatant fluid was pooled and again centrifuged at 90,000 X g for 2 hours in a Model L Spinco centrifuge (Beckmann Instruments, Palo Alto, Calif.) to pellet the virus. The pellets were resuspended into the lower one milliliter portion of the supernatant, pooled, and clarified by discarding the sediment after centrifugation at 12,000 rpm (17,000 Xg)for 5minutes. The supernate was frozen and stored at —18°C until used as inoculum. Samples of all BPV inoculums were negatively stained and examined under the electron microscope to ascertain the presence and relative con centration of virions in the virus inoculums. Finely ground carbon particles were suspended in the BPV inoculums to mark the inoculation site for future reference during examina tion of inoculated tissues with the light microscope. Penicillin and streptomycin were added to insure a more aseptic inocu lum. Twenty one-week-old calves, predominantly dairy breeds from herds that were allegedly free of cutaneous fibropapillo matosis, were used in this study. Selected sites in the nervous, integumentary, circulatory, digestive, respiratory, and urogeni tal systems were inoculated with BPV suspensions (Table I).