58 



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



than ninefold). From this table it is seen that, as would be expected, the 

 tracheal area (sectional area of the trachea) increases much more slowly 

 than the body weight, so that the ratio of the tracheal area 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 «th power (where n 

 is approximately O70-0'72) divided by the sectional area (T) is a constant (k). 



This gives the formula W"/T = k, which indicates that the tracheal area 

 (area of the cross-section of the trachea) is a simple function of the surface of the 

 body, since, as we have shown, the body surface may be determined accurately 

 from the formula S = £.W" by taking n to be approximately 0'70-O72 

 instead of f , as was done by Meeh (6). 



Table I further shows that the average value of k is 23 - 4, corresponding to 

 an n of - 72, which is by calculation the best n for these observations, and 

 that if the tracheal area be calculated from the formula T = W n /k, using 

 these values for n and k, the average percentage deviation of the observed 

 from the calculated values is 18*2. If, on the other hand, the sectional area 

 is expressed in percentage of body weight (0'908), the average deviation 

 between the calculated and the observed values is 25"1 per cent. 



It may be stated further that if the value - 71 is taken for n, the average 

 value of k becomes 21 - 5. 



To bring out the various points more ■ clearly, as well as to get rid of 

 irregularities due to individual variations in the animals and to experimental 

 errors, the animals have been grouped in Table II. 



The guinea-pigs are arranged in five groups according to weight, and the 



Table II. — Guinea-pig (grouped). 



Group. 



Numbers of individuals 

 from Table I in 

 group. 



Average body weiglit. 



Average radius of 

 tracliea. 



Average area of tracheal 

 cross-section. 



h 

 n 



Tracheal cross-section 

 as percentage of body 

 weight. 



Cross-section calculated. 

 {h = 21 -3.) 



Difference between 

 cross-section calcu- 

 lated and observed. 



Cross-section calculated 

 as percentage (0 "965) 

 of body weight. 



Difference between 

 cross-section calcu- 

 lated and observed. 







grms. 



mm. 



sq. mm. 









per cent. 





per cent. 



A 



1 



70 



-605 



1 -06 



19 3 



1 -51 



-959 



10 53 



0-676 



56 -8 



B 



2-6 



214 



0-785 



2 02 



22 -4 



0-944 



2 12 



4-72 



2-07 



2 -42 



C 



7-10 



345 



986 



3 -09 



20 -5 



896 



2 98 



3 69 



3 33 



6 31 



D 



11-14 



453 



1 -074 



3 65 



21 -1 



0-806 



3 -61 



1 11 



4-37 



16 -48 



E 



15-16 



630 



1 159 



4-23 



23 



671 



4 56 



7-24 



6-08 



30 43 









Avera 





21 3 



965 





5-46 





22 -49 



