1912.] The Size of the Trachea in Warm-Blooded Animals. 57 



and many of them were made use of at the same time for measuring the size 

 of the aorta. The guinea-pigs and rabbits had all been kept in the laboratory 

 under as equable conditions as possible as regards food, etc. Pregnant 

 animals were, of course, excluded. The ptarmigan were purchased from a 

 game dealer, and were carefully selected. 



Methods. — The technique employed was identical with that described in a 

 previous paper (4) for the determination of the size of the aorta. The 

 internal ttt of the trachea was carefully measured at a point just above its 

 bifurcation, and from this the radius and the sectional area were determined. 

 As we have pointed out before (4), the method made use of is open to 

 considerable experimental error, but this is greatly reduced by multiplying 

 the number of individual observations of each trachea, and also diminishes 

 greatly with increasing practice. The body weights recorded are the natural 

 weights (in grammes) of the animals immediately before they were killed, 

 and consequently include the weight of the contents of the alimentary canal. 



Table I. — Guinea-pig (individuals). 



6 



Sex. 



Body weight. 



Eadius of trachea. 



Area of tracheal cross- 

 section. 



En 



o 



II 



Tracheal cross-section 

 as percentage of body 

 weight. 



n 



- o CO 



•a 1 : n 



§ 11 « 



GO 

 CO 



o 

 O 



Difference between 

 cross-section calcu- 

 lated and observed. 



Gross-section calculated 

 as percentage (0 '908) 

 of body weight. 



Difference between 

 cross-section calcu- 

 lated and observed. 







grm. 



mm. 



sq. mm. 









per cent. 





per cent. 



1 



3 



70 



-605 



1 06 



20-1 



1 52 



91 



16 5 



635 



67 



2 



? 



170 



814 



2-46 



16 4 



1 45 



1-72 



43 -0 



1 -54 



59 8 



3 



3 



220 



745 



1 -74 



28 -0 



791 



2 -08 



16 3 



2 



13 



4 



? 



220 



892 



2 5 



19 4 



1 -14 



2 08 



20 -2 



2-0 



25 -0 



5 



X 



230 



742 



1 73 



29 



753 



2 15 



19o 



2 19 



21 



6 



? 



230 



733 



1 -68 



29 9 



0-73 



2 15 



21 -8 



2 19 



23 3 



7 



3 



300 



796 



1 -99 



30 4 



664 



2-58 



22 -8 



2 -72 



26 -8 



8 



3 



330 



1 -035 



3-36 



19 4 



1 02 



2 -78 



15-1 



3 



12 



9 



? 



360 



1 031 



3 -34 



20-7 



0-928 



2-96 



12 -8 



3 -27 



2 14 



10 



¥ 



390 



1 -082 



3-68 



19 -9 



0-944 



3 13 



17 6 



3 54 



3 96 



11 



9 



410 



1 -157 



4-2 



18 1 



1 02 



3 24 



29 -6 



3-72 



12 -9 



12 



3 



420 



-97 



3 



25 8 



714 



3 31 



9-36 



3 81 



21 -2 



13 



3 



490 



988 



3 06 



28 3 



0-625 



3 79 



17 -3 



4-45 



31 -2 



14 



3 



493 



1 179 



4 35 



20 -0 



0-883 



3-72 



16-9 



4-48 



29 



15 



¥ 



620 



1 115 



3 90 



26 2 



629 



4 37 



10 "7 



5 63 



30 -8 



16 



¥ 



640 



1-203 



4 "55 



23 



711 



4 47 



1-79 



[ 



5 81 



21 -7 









Avera 



ge 



23 "4 



908 





18 2 





25 1 



Observations. — In Table I are given the figures and calculations for 

 16 guinea-pigs, ranging in weight from 70 to 640 grm. {i.e. increasing more 



