CLASSIFICATION.—A rigorous classification of the different kinds of pulmonary emboli or a clear separation of them into distinct orders is very difficult on account of the rôle in producing them, partly mechanical, partly dyscrasic, of some of the affections in which they are likely to occur. This is particularly true of the puerperal state, uterine affections, and fractures.1 Bertin, however, has made of them four divisions, according as the cause is mechanical, dyscrasic, mixed, or undetermined; but these are objected to by Luzzato on the ground of their inadequacy, and he deems it preferable to regard them from the point of view of their medical, surgical, or obstetrical origin. From this latter point of view we also consider it best to consider them until a more satisfactory separation shall be established.
HISTORY.—Latterly, the subject of pulmonary embolism, or the obstruction of this artery by means of a clot which has had its origin in the right heart or one of the systemic veins, has been very carefully studied. Many cases of sudden death are properly and readily explained in this manner, where formerly they would have been doubtful or inexplicable. Sometimes the previous existence of a fibrinous coagulum in the right heart or in the crural vein has been recognized previous to the symptoms indicating plugging of the pulmonary artery; occasionally these coagula have been wholly overlooked, and the sudden cry with intense dyspnoea, pointing to obstruction of the blood-supply to the lungs, is a matter of dread surprise to the beholder. According to Trousseau,2 our knowledge of embolism is due mainly to Legroux. This is not, however, the view of Ball3 nor of Walshe, who attribute the clearest insight into this process to the clinical and experimental observations of Van Swieten, who, half a century before Legroux's time, had injected different coagulating materials into the veins of animals and produced the characteristic symptoms of pulmonary embolism. To Virchow's4 exhaustive researches, however, we are principally indebted for a great deal of what is actually known upon this subject to-day. True it is that contemporaneous writers have added many new facts to those he so well elaborated, but the greater part of credit in this line of study should be awarded to him. After Van Swieten's time the doctrine of pulmonary embolism fell somewhat into disrepute, owing to the lukewarmness of Hunter and Morgagni. Cruveilhier (1842) recognized their existence, but was so much impressed by his doctrine of phlebitis that he believed the majority of pulmonary coagula were autochthonous (formed on the spot), and not the consequence of transport or migration in the venous current. This opinion was strongly combated by Virchow, who held that pulmonary coagula formed some time before death were not the result of an inflammation of this arterial vein (Galien), but always had for origin a migratory clot which came from some part of the venous system.5 This doctrine of Virchow's is certainly too exclusive, and although primary or secondary inflammation of the pulmonary artery is certainly rare, it is certainly not unknown, and when it exists will sufficiently explain the formation of a fibrinous clot. Facts of this kind have been reported by Bumann, Bouillaud, Andral, and more recently still by Lancereaux, who has shown to the Anatomical Society of Paris6 distinct new formations in the pulmonary artery. Until further investigations are made on this point it seems wise to abstain from having an opinion too categoric on one side or the other. Virchow's first studies on pulmonary embolism were published in 1846, and were based upon 11 cases of this disease. All these cases were caused by migratory clots from the heart or one of the systemic veins. In this first publication, and later on (1854–56), Virchow gave the results of numerous experiments in which he had injected bits of fibrin of diverse origin, particles of flesh, and fragments of rubber into the jugular veins, and showed in an admirable description the immediate effects of embolic plugs upon the blood, the arterial coats, and the surrounding pulmonary tissues.7
1 Étude critique de l'Embolie, Paris, 1869.
2 Clinical Lectures, Sydenham Society's ed., vol. iii. p. 414.
3 Des Embolies pulmonaire, Thèse de Paris, 1862.
4 Froniep's Neue Notizen, 1846, p. 910.
5 Bucquoy, Des Concrétions sanguines, Paris, 1863, p. 138.
6 Bullétin, 1861, p. 377.
7 Dict. de Médecine et de Chirurgie, vol. xxix. p. 334.
In 1852, Senhouse Kirkes8 also studied very carefully different cases of embolism, and showed how they were connected with organic disease. Most of these cases, however, showed rather the effects on the brain and the production of right or left hemiplegia than the asphyxic sequelæ of obstruction of the trunk or divisions of the pulmonary artery. In France the doctrine of embolism was at first received doubtingly, and was the subject of animated discussions at the Medical Society of the Hospitals in 1857. In this year Charcot and Ball published the first case of pulmonary embolism which had been observed in that country. Five years later (1862) pulmonary embolisms formed the subject of a remarkable inaugural thesis by Ball, and articles of considerable value were also written in regard to it by Velpeau, Lancereaux, Lemarchand, Trousseau, etc. Spontaneous coagulation of the blood in the right heart and pulmonary artery was considered by Meigs in 1855 to be a frequent cause of death in the puerperal state. Analogous cases, although none of them occurred after childbirth, had five years previously been carefully studied by Paget.9 The cases of sudden death subsequent to confinement are now generally considered to be due to pulmonary embolism.10 Amongst the later sources of information on the subject of pulmonary embolism or its consequences we would direct special attention to the work of Luzzato11 and the theses of Duguet12 and Levrat.13 These and numerous other writers have made researches as to the different varieties of pulmonary embolism, such as the fatty (Flournoy), atmospheric, specific, those following confinement, or traumatism.