ETIOLOGY.—We know scarcely anything of the causes of the disease, but it is usual to take into account certain factors which may possibly influence its production, such as climate and country, age, sex, etc.
Climate and Country.—The disease appears to be more common in temperate regions; not many instances are reported from the tropics. It does not appear to be often met with in India. It is, I think, more common in Europe than in this country. The determination of its prevalence is rendered difficult by the fact that many cases reported simply as enlarged spleen, without any examination of the blood, have possibly been leukæmia. It does not seem to be more common in the southern part of this continent.
Age.—No age appears exempt. Cases are recorded in infants of eight or ten weeks and in men of sixty-nine and seventy years of age. The youngest case I have seen was in a suckling of eight months. The majority of cases occur at the middle period of life, from thirty to forty. After the fiftieth year the cases diminish very much in number.
Sex.—Males are more prone to the affection than females, in the proportion of at least 2 to 1. Of 11 cases which I saw in Montreal, only 3 were in females; of 200 cases collected in the literature, 135 were in males and 65 in females (Birch-Hirschfeld103).
103 Lehrbuch der Path. Anatomie, 2te Auf., 1883.
Social and sanitary conditions do not appear to have much influence, though the lower and middle classes furnish the majority of the cases. Mental worry and depression are specially mentioned as predisposing causes in some cases.
Previous Disease.—In women it has frequently been noticed that disturbance in the menstrual and sexual functions has preceded the onset of the disease. The climacteric period has the greatest number of cases, and in a few instances the disease had developed during pregnancy.
The hemorrhagic diathesis has been noted in many cases, and the patient may have been the subject of slight hemorrhages for years. In one case of Howard's104 the lad had been subject to nose-bleeding as a child, and his mother and one sister had been much troubled in the same way.
104 Montreal Gen. Hosp. Reports, vol. i., 1880.
Malaria.—On account of the frequency of chronic splenic tumor in malarial infection, inquiries are always carefully made in any suspected case as to the occurrence of intermittent fever. An intimate connection is believed by certain writers to exist between the affections, and a few cases seem to have followed directly upon chronic malaria. In Mosler's statistics of 112 cases there were only 4 in which the sequence was well marked.105 In Gowers' 150 cases there was a history of malaria in 30.106 In the Montreal cases there was an account of malaria in 3 certainly—possibly in a fourth. In the reports of 33 American cases there were only 6 with a history of malarial attacks within twelve years from the date of the onset of leukæmia. Guiteras of Key West (now of Charleston, S.C.) states that it is a rare affection in the South. Schmidt of New Orleans writes me that it is not uncommon in Louisiana, but there are very few cases reported in Southern journals.