STUDIES ON THE PANCREAS OF THE GUINEA PIG 319 



Technique. The sources of error in this method of estimation 

 of the ratio of number of islets to weigh are, in addition to those 

 which influence the accuracy of the count, loss of weight or in- 

 crease of weight owing to the salt solution being hypotonic or 

 hypertonic, loss of weight from the solution of cell proteins, and 

 inequalities from the comparative standpoint in the amount of 

 water abstracted in drying. The question as to the extent of 

 these errors I have tested by comparative weighing of pancreases 

 of guinea pigs of the same litter in the same physiological condi- 

 tion, and also by comparing the ratios of the weights of several 

 pieces of the same pancreas with the ratios of the weights of several 

 pieces of the same pancreas with the ratios of the dried weights 

 of the same pieces. Of the two male guinea pigs weighing respec- 

 tively 302 and 304 grams and aged forty days, one was injected 

 with neutral red, counted, and the pieces of pancreas collected 

 and weighed, the other's pancreas was freed from fat and weighed 

 without injection. The total weights of the pancreas were re- 

 spectively 1,118 grams and 1.104 grams, the heavier being from 

 the injected guinea pig. Similarly two new born guinea pigs 

 weighing 55 and 57 grams respectively gave the weights 0.113 and 

 0.110 for the pancreases, the heavier being again the injected 

 pancreas. As tested by the comparison of the ratio of dried 

 weights to one another with the ratio of the corresponding wet 

 weights of the same pieces, the greatest difference found was 13 

 per cent. 



In table 2 the splenic portion included the omental portion of 

 the pancreas cut off flush with the dorsal posterior extremity 

 of the spleen, the duodenal portion included that part of the pan- 

 creas on the right of a line from the superior mesenteric vessels 

 to the pylorus, the body included the rest of the pancreas between 

 the other two. 



In this series of forty-six guinea pigs the splenic portion shows 

 the highest average content of islets in 39, and is second in 7. 

 The body of the pancreas is highest in 7, second in 29, and third 

 in 10. The duodenal portion is first in none, second in 10, and 

 third in 36. Thus the condition found in the human pancreas 

 by Opie ('00) is found to hold true for the guinea pig. 



