Spontaneous Tumors of the Rat

Abstract

Several years ago the writers (1) developed a simple and practical method of producing sarcoma of the liver of rats by infesting these animals with Cysticercus fasciolaris, the larva of Taenia crassicollis, the tape worm of the cat. These experiments, which have been pursued uninterruptedly since their inception, in October, 1919, were started with 548 purchased rats and from these 1819 unpedigreed descendants of the first generation were added to the experiments. Breeders were then selected from these purchased animals and their unpedigreed descendants and a pedigreed rat colony was established which has furnished the animals for the later studies on the neoplasms associated with Cysticercus fasciolaris. The size of this colony increased gradually for several years but for the last four or five years it has fluctuated from 7,000 to 10,000, the latter being the maximum capacity of the animal rooms at our disposal. The experiments are still in progress but reports on several phases of the work have appeared in this Journal (2, 3, 4, 5, 6, 7). The object of the present communication is to consider the tumors which have arisen in the rats of this colony without any direct etiological relationship to Cysticercus fasciolaris. For these neoplasms the term “Spontaneous tumors” will be employed to distinguish them from the experimentally induced Cysticercus tumors, though we realize that a spontaneous tumor is only one of which we do not at present know the causative agent.