42 Messrs. Dreyer, Ray, and Walker. [Sept. 30, 



expected, the radius of the aorta increases much more slowly than the weight 

 of the animal. The area of the aortic cross-section also increases more 

 slowly than the body weight (though of course much more rapidly than the 

 radius), so that the ratio of the sectional area of the aorta to the body weight 

 decreases steadily as the weight of the animal increases. But it appears on 

 calculation that the body weight (W) to the nth power (where n is approxi- 

 mately O70-O72) divided by the sectional area (A) is a constant (k). 



This gives us the formula W"/A = h, which indicates that the sectional 

 area of the aorta is a simple function of the surface of the body since, as was 

 shown in a previous paper, the body surface, which can be calculated from 

 the formula S = JSW n is more accurately determined by taking n to be 

 approximately , 71—0 , 72 than by taking it equal to 2/3 as was done by 

 Meeh (5). Now it has been proved on former occasions that tbe blood 

 volume is proportional to the body surface, hence it follows that the sectional 

 area of the aorta is proportional to the blood volume of the individual. 



Table I further shows that the average value of k is 24 - 9, corresponding 

 to an n of - 71, which is by calculation the best n for these individuals, and 

 that if the aortic cross-section be calculated from our formula A = W n /Jc 

 using these values for n and h, the average percentage deviation between 

 calculated and observed values is 16 - 44. If, on the other hand, the sectional 

 area is expressed as a percentage of the body weight (078), the average 

 deviation between the calculated and the observed values is 19 - 68 per cent. 



It may be stated further that if the value 072 is taken for n, the average 

 value of h becomes 26'5, and, if the sectional area is calculated from 

 A = W°' 72 /26 - 5, the average percentage deviation between the calculated and 

 the observed figures is found to be 16*53. 



In order to bring out the various points more clearly, to get rid of 

 irregularities due to individual variations in the animals, and to diminish the 

 influence of experimental error, the animals have been grouped in Table II. 



In this table the guinea-pigs are arranged in five groups according to 

 weight, and the weights, the aortic radii, and the aortic cross- sections of the 

 animals in each group averaged. The other figures are calculated from these 

 average values. 



It is found that, under these circumstances, the best n is 0*72 (exactly as- 

 we found to be the case in calculating the surface from the body weight), 

 and the average value of h is 25 - 6. Using these values for n and k, the 

 average deviation between the calculated and the observed figures is 2 - 97 per 

 cent., whereas, if the sectional area be calculated as a percentage (0 - 78) of the 

 body weight, the average percentage deviation becomes 14 - 2, that is to say, 

 nearly five times as large. Moreover, it will be observed that, while the Jc 



