362 H. B. ANDERVONT 



Schwartz et al. (1956) prepared filtrates from the brains of high-leukemia 

 strain AKR mice with spontaneous, transplantable, or induced leukemias 

 and injected the nitrates into other AKR mice which were over 4 weeks old. 

 The inoculated animals were killed when 22 weeks of age, when between 45 

 and 100 % had developed leukemia. Of 229 AKR mice inoculated with 

 various control materials, none showed evidence of a similar acceleration of 

 the leukemic process. Engelbreth-Holm and Frederiksen (1938) and Rudali 

 et al. (1956) also observed an acceleration in the appearance of leukemia in 

 strain AKR mice after they got cell-free extracts of AKR tissues. In a later 

 paper Schwartz et al. (1957) reported, with similar procedures and the use of 

 3-to 16-week-old AKR mice as test animals, the early occurrence of leukemia 

 following injections of nitrates prepared from the brains of patients who had 

 died of acute leukemia. Control materials, consisting of heat-treated filtrates 

 from the same patients, did not hasten the appearance of leukemia in AKR 

 mice. It is regrettable that a few mice from a low-leukemia strain were not 

 used along with those of the AKR strain. 



In another communication from this group of workers (Schoolman et al. 

 1957) mice over 4 weeks of age were used. Briefly, a spontaneous leukemia 

 arising in a Swiss mouse (apparently noninbred) was transplantable, to a 

 limited extent, in other Swiss and inbred DBA mice. Filtrates from these 

 Swiss or DBA tumors failed to produce tumors in Swiss mice, whereas 

 filtrates from brains of tumor-bearing Swiss or DBA mice evoked leukemia in 

 Swiss or DBA mice. Strangely, filtrates from leukemic brains of either strain 

 failed to accelerate the occurrence of leukemia in AKR mice. The investigators 

 stated the crux of their problem as follows: "The nature of the agent in these 

 filtrates has not been defined," but the closing statements in their paper give 

 the impression it was transmissible in serial passage. 



Graffi (1957) has recently summarized the work of another group of investi- 

 gators interested in problems of mouse leukemia. Space does not permit a 

 thorough discussion of this review, but these workers have detected agents in 5 

 transplantable mouse tumors which, when administered to test animals, 

 induced myeloid leukemias, "chloroleukemia," instead of the usual lymphatic 

 leukemias obtained by others. Newborn mice and adults were used as reci- 

 pients for tumor filtrates, but the review contained few references to the use 

 of adults. Mice from birth to 11 days of age were equally susceptible to 

 filtrates from one sarcoma and even mice 3 to 4 months old were "rather" 

 susceptible. 



Other interesting findings were: (1) No chloroleukemias were found in mice 

 treated with embryonic tissues from mice, rats, or chickens. (2) Tissue 

 cultures of mouse embryos were inoculated with tumor filtrates, and, after 

 one or more passages, were filtered and the filtrates injected into newborn mice. 

 The results were negative, but the inocula were "very toxic." (3) The agent in 



