Among the most constant secondary lesions is the aggregate of changes known as those of pulmonary phthisis. But a few years ago, when our ideas on this subject were more definite than they are to-day, and when it was thought we had three distinct varieties of phthisis--the tubercular, the catarrhal, and the fibroid--the phthisis of diabetes was regarded as typically catarrhal.[15] At the present time, however, when the tendency at least is to regard all phthisis as tubercular, diabetic phthisis must be consigned to the same category. At the same time, if the tubercle bacillus is to be regarded as the essential criterion of tuberculosis, it must be stated that the diabetic patient is subject to two different lung processes--at least if the observations of Riegel of Giessen[16] are to be regarded as correct. In two cases of diabetic phthisis studied at his clinic, the sputum of one contained numerous bacilli, while the other, although the case presented the most distinct signs of infiltration of the apex, and although more than fifty preparations were investigated, revealed none. The sputum was also said to present some unusual physical characters. So far as I know, no autopsies of cases showing these clinical differences have been reported, although there have been found in diabetes, distinct from the usual cheesy foci, fibroid changes with small smooth-walled cavities. In such cases {203} tubercle bacilli would be absent, while the physical signs of consolidation would be present. [Footnote 15: See the writer's work on _Bright's Disease and Diabetes_, Philada., 1881, p. 256.] [Footnote 16: _Medical News_, Philada., May 19, 1883, from _Centralblatt f. klin. Med._, Mar. 31, 1883.] As a part of the phthisical process in diabetes, cavities of various sizes are found and gangrene of the lungs has been observed. ETIOLOGY.--The problem of the etiology of diabetes mellitus is as unsatisfactorily solved as is that of its pathogenesis. Certainly, a majority of cases of diabetes cannot be accounted for. A certain number may be ascribed to nervous shock, emotion, or mental anxiety; a few to overwork; some to injury and disease of the nervous system; others to abuses in eating and drinking. Among the injuries said to have caused diabetes are blows upon the skull and concussions communicated to the brain, spinal cord, or vaso-motor centres through other parts of the body. Hereditation is held responsible for a certain number of cases. Malarial and continued fevers, gout, rheumatism, cold, and sexual indulgence have all been charged with producing diabetes.