Relative Sizes of the Organs of Rats and Mice, etc. 287 



blood-clots removed from its cavities. The unopened alimentary canal was 

 first weighed, then split open throughout its length and washed with 

 0"75-per-cent. salt solution till the wash-water remained clear. It was then 

 dried rapidly between filter-paper. All the organs were weighed in closed 

 weighing bottles, after which the moisture was driven off in a drying oven 

 kept at 103° to 105° C. for 40 to 50 hours, and the weight of the dry 

 substance determined. The tumour weights include the fluid and necrotic 

 parts as well as the growing parenchyma. Hence, in comparison with the 

 results obtained from normal animals, especial weight must be laid on the 

 ratios of the weights of organs to hody-weights minus tumour. 



Normal Ratios. 



A large number of normal mice belonging to different age-periods were 

 examined. The variations due to age are most marked when the animals 

 pass from a milk (sucking) to a vegetarian (adult) diet. The alimentary 

 canal is relatively twice as heavy in animals a few days after the establish- 

 ment of vegetarian diet as at nine days (milk diet). During the remainder 

 of life the ratio remains fairly constant with a slight diminution in old age. 

 Nearly identical variations are presented by the liver. Heart and lungs are, 

 on the contrary, relatively larger in sucking mice. The kidney shows only 

 small variations, whether we compare animals of different ages or individuals 

 of the same age. The spleen varies enormously, but is relatively smaller 

 in sucking and young animals than in adults. It follows that comparisons 

 are only allowable between animals of the same age. Equally extended 

 observations have not been considered necessary in the case of rats, and in 

 these the control observations have been restricted to normal animals of the 

 same weight as the tumoiir-animals. Considerations which will be fully 

 dealt with in a later paper led me to undertake experiments in which rats 

 were fed with a uniform diet (150 c.c. milk, 350 grammes rice or oatmeal, 

 and 60 grammes bread) for several weeks or months. The weight-ratios of 

 some organs were found to be modified by this diet, e.g., those of the alimentary 

 canal, heart, and kidneys were relatively smaller, that of the lungs larger, 

 and that of liver unaltered. A number of tumour-rats were fed on the same 

 diet, and the control estimations are taken from normal rats correspondingly 

 fed. In the same way the tumour-rats fed on the ordinary laboratory diet 

 are compared with similarly fed normals. 



Ratios in T^imour-animals. 



Alimentary Canal. — The general impression of all the estimations has been 

 that, under the experimental conditions thus far investigated, the relative 



