Cancer research to-day includes three separate departments :
I. THE PARASITIC THEOEY.
Since the seventeenth century, and the time of Lusitanus, medical literature has contained numerous reports of the contagiousness of cancer. It has been claimed that the disease arises in epidemics; that it is increasing in frequency ; that it exhibits, in certain localities, a significant relation to the soil and water; that it is transferred from one human being to another; that it may be inoculated into lower animals; while many have claimed to have identified the parasitic cause of its contagion.Endemic Occurrence of Cancer.—The observations on the endemic occurrence of cancer, under current discussion, relate to the discovery of many tumor animals in the stock of one breeder, to the frequency of cancer of the