Weigert was the first to stain bacteria. He introduced many of the best staining methods in use today. Weigert discovered bacteria in hemorrhagic smallpox. In the same paper is described how carmine will color cocci.

In the course of his important studies on smallpox, Weigert carried out the first successful staining of bacteria (see No. 2482). His fine description of the destructive effects of the smallpox virus on the skin led to the coining of the term “coagulation necrosis” as a name for the process causing the development of the lesions.

In this paper Weigert showed that methyl violet will reveal cocci in tissues.

Classic study of the pathological anatomy of Bright’s disease.

First description (p. 106) of myocardial infarction. Leibowitz called this "the most significant contribution by a pathologist to the history of coronary heart disease." He also wrote, "This work not only provides a general description of myocardial changes following a coronary thrombosis, but also includes a very important detail, namely that of the destruction of cell nuclei. Likewise it stresses also the clinical history, since pathological findings largely depend upon the time factor" (Leibowitz, History of coronary heart disease).

Weigert noted the connection of myasthenia gravis with hypertrophy of the thymus.