The illness caused pathological changes in the intestinal mucosa, mesenterium, heart, and lungs. As realized later, the same disorder had previously been described by Allchim and Hebb in 1895 but they had failed to recognize it as a new disease. Based on the presence of unsplit fat in the stools, intestine, and mesenteric glands, a disease of fat metabolism was supposed. “Rod-shaped organisms in silver-stained gland tissue, closely resembling the tubercle bacillus” were observed but not considered the etiology of the disease. However, no other tissue was available for further analysis. The histological criteria for Whipple's disease were summarized by Black-Schaffer in 1949, periodic acid-Schiff reagent (PAS) was used to stain inclusions in macrophages found in the intestines and mesenteric lymph nodes of patients with this disease. With the help of electron microscopy free rod-shaped bodies with an outer membrane were noticed in the lamina propria. The authors considered the possibility of virus-like particles. A probable bacterial etiology of Whipple's disease was first considered in 1961 based on light and electron microscopy.