328 PATHOLOGY 



very commonly present in all rats over two years of age. In 

 some colonies middle ear infection frequently occurs and produces 

 disequilibration and circular movements. Such rats when 

 held up by the tail execute a spinning movement. This is 

 diagnostic. In the Institute colony at present middle ear disease 

 is found in about one per cent of the animals. 



These two ailments are the most common ones observed. 

 From time to time animals come to autopsy with organs missing on 

 one side and other defects, both congenital and acquired, but a 

 detailed study of these has yet to be made. 



3. Toxicology. The studies of Hammett and Nowrey ('22 b) 

 show that with advancing age there is a progressive diminution 

 in the resistance of the albino rat to death from arsenic poisoning. 

 A dose of 11 mgm. per kilo or over of arsenic trioxide is fatal to 

 young rats of 60 to 90 days of age. By the time the animals 

 have reached the age of 120 to 150 days a dose of 9 mgm. is 

 fatal. When they are 210 to 240 days old, 8 mgm. is the amount 

 which produces death within 24 hours in the average animal. 



These differences in susceptibility with age are attributable 

 in large part to differences in metabolic rates. 



It is to be noted also that the proportional weight of the 

 abdominal and thoracic viscera decreases in nearly the same 

 proportion that the fatal dose decreases. 



PATHOLOGY: REFERENCES 



Pathology general. Advisory Committee, '12 a. Alexander, '01. Ascher, 

 '10. Aumann, '12. Aunett, '08. Bainbridge, '09. Berthelot and Bertrand, 

 '12. Bircher, '11. Bradley and Sansum, '14. Carini, '15. Czerny, 1890. 

 Davis, '16. Dobell, '13. Emmett and Allen, '20. Hirschfelder, Hart and 

 Kucera, '20. Klein, '02, '06. Kulyosha, 1899. Langhans and Wegelin, '19. 

 McCollum, Simmonds and Kinney, '22. McCoy, '08 a. Mallory and Ordway, 

 '09. Merezhkovski, '03. Mereshkowsky and Sarin, '09. Metschnikoff and 

 Roux, 1891. Nerking, '09. Nierenstein, '12. Noguchi, '19. Ochsner and 

 Thompson, '10. Ophuls, '11. Ordway and Morris, '13. Osborne and Mendel, 

 *17b . Pappenheimer and Larimore, '23. Reed, '00. Rous and Jones, '16. 

 Safford, '18. Schern, '09. Schilling, '00. Schurmann, '08. Smith, '21. 

 Suzuki, '04. Tartakovski, '02. Tenbroeck, '18. Trautmann, '06. Wherry, 

 '08 b. Wiener, '02. Wolbach, Chapman and Stevens, '15. Xylander, '06. 



Malformations. Conrow, '15, '17, '17 a. 



