Scientific Proceedings (69). 



The colorimetric method will be found of great value in the 

 adjustment of the hydrogen ion concentration of media for organ- 

 isms which are sensitive to the reaction of their culture fluids. 

 The method is comparable in a way to the fine adjustment of a 

 microscope. The method of titratable acidity serving only to 

 adjust media coarsely for the growth of the average organism. 



17 (1081) 



Sarcoma occurring in a guinea-pig. 



By Ernest C. Dickson, M.B. 



[From the Division of Medicine of Stanford University Medical 



School. 



On May 10, 1915, a large male guinea-pig which had seemed to 

 be in good health in the morning became suddenly ill in the 

 afternoon and died within a short time. The animal had been 

 injected some months previously with a culture of what was 

 supposed to be diphtheria bacilli, but it had survived the injection. 

 At autopsy a large freely movable mass was found in the mid-line 

 of the neck on the ventral surface, which was adherent to the 

 underlying tissues about mid-way between the lower jaw and the 

 shoulder girdle. The tumor was apparently encapsulated and 

 showed no attachment to the skin. It measured 3^ x 2Y2 x 2Y2 

 cm. in the various diameters, was yellowish in color and quite firm. 

 The capsule was fibrous and cut with some difficulty, but the 

 central portion was quite friable. The cut surface was yellow 

 with many mottled patches which were dark red in color. 



Surrounding the tumor and in the right axilla were a number 

 of metastatic nodules, the largest of which measured 1 Y x 1 x 

 cm., and the smallest being about the size of a grain of wheat. 

 Section of the larger nodules showed a cut surface which was 

 identical with that of the large tumor. 



The thoracic and abdominal organs showed nothing unusual. 



On microscopic examination the body of the tumor is seen to 

 consist of round and ovoid cells which vary considerably in size. 

 In places the cells are closely packed together but in others they 

 are separated by a reticulum of connective tissue. There are 



