1. Departments of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
2. *Pathology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA
3. Division of Cell Biology and Experimental Cancer Research, Institute of Pathology, University of Berne, Berne, Switzerland
4. Anatomy, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853, USA