loci instead of being repeated on the same spot lung tumors rather than tumors of the skin are induced. For 3 of these stocks data are already available after using this technique. The animals were killed on the 300th day, thereby giving uniformity as to age. For the skin tumor experiment also the percentages are cited for the 300th day. The Bagg ( a ) group had a high incidence of lung tumors (92.8 t 2.1%) and a low percentage of skin tumors (13.2 * 2.6%).In Strain 62 the situation was reversed. There were only 12.9 t 4.1 % lung tumor and a higher incidence of skin tumor (51.8 t 4.5 %). Strain 1194 showed about the same degree of susceptibility to tumors in the 2 organs (22.4 t 4.0 and 21.1 t 2.8% respective-Data taken at the conclusion of the experiment in which the skin tumor technique was employed while not furnishing as strict a comparison provide additional evidence. The relationships here are similar to those already found except that in the 1194s the tumor incidence of the skin is now higher (42.1 2 3.4%) than that of the lung (16.2 t 2.9%). Both groups of Bagg mice have high lung tumor rates (81.5 t 3.2 and 80.0 t 6.0% respectively), and significantly lower skin tumor rates (34.2 t 3.7 and 4.3 t 2.9%). The members of Strain 62 did not live long enough to give information as to their lung tumor susceptibility but the hairless mice show a high incidence of both tumor types (73.6 t 4.1 % skin tumors and 73.8 +-4.6% lung tumors). Evidently there is no correlation between the susceptibilities to tumor in the 2 organs.If these types are inherited separately there must be separate genes to represent them in the germplasm. More than one pair of Mendelian factors must be involved, though the exact number is undetermined. ly).

Kelser's demonstration (1) t h a t Agdes aegypti will transmit the virus of equine encephalomyelitis from infected to normal guinea pigs provides an almost ideal combination for the study of insect transmission of this type of infection. The mosquitoes can be raised with ease the year round, and guinea pigs are highly susceptible to the virus, which produces in them a characteristic disease. I t is our purpose to record here certain observations t h a t followed a t t e m p t s to confirm Kelser's work. MethodsTo Dr. A. Watson Sellards we are indebted for the original stock of A~tes aegypti eggs as well as directions which enabled us, with the assistance of Dr.Lacaillade, to establish a colony quickly. For transmission experiments females that had recently emerged and that had never been given a blood meal were transferred to small screened cages. These mosquitoes could be infected by feeding either on a guinea pig inoculated with encephalomyelitis virus or on a mixture of the brain from an infected guinea pig and defibrinated horse blood. When mosquitoes are to be fed on a living animal, their food, consisting of 3 per cent sugar solution, is withheld for 3 days. They will then readily attack a guinea pig that is immobilized and placed in their cage. The infection of mosquitoes by feeding on a mixture of virus and blood requires a more careful preparation of the insects. For 4 days they are allowed only water and this is withheld the night before they are fed. The mixture then offered them consists of a 10 per cent suspension of brain from an infected guinea pig in saline and an equal part of defibrinated horse blood. A pledget of cotton in each of two small Petri dishes is moistened with the mixture and a little powdered sugar is sprinkled over the surface. One dish is placed in the refrigerator and the other in the cage. The hungry mosquitoes feed on the mixture, which is allowed to remain in the cage for an hour and is then replaced by the one that has been held in the refrigerator, since it is known that the virus deteriorates rapidly at room temperature. By withholding water for 1 day and sugar solution for 2 days the mosquitoes that have 687 on

The major part of this investigation comprised a thesis presented to the Committee on Graduate Studies of the St. Louis University School of Medicine in partial fulfillment of the requirements for the degree of Master of Science.

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