1070 



THORAX. 



edge of the scapula, then he feels the expand- 

 ing effect of inspiration, the swelling up of 

 the apex of the thorax. 



To determine the volume of air in the spi- 

 romcter. The graduated scale 13 is attached 

 to the receiver, and made to extend down- 

 wards on the outside of the reservoir, so as 

 always to he in relation with the index 2. 

 On this scale corresponds with the top of the 

 receiver, or rather with the highest point to 

 which the water can be made to rise within 

 it. The number of cubic inches is shown by 

 the degree upon the scale pointed to by the 

 index 2, which corresponds with the level 

 of the water in the receiver. But the 

 water in the reservoir seen behind the slip 

 of glass may not be level with the water 

 within the receiver, just as the level of 

 the water in a pneumatic trough may be 

 higher or lower than the level of the water 

 contained in a glass receiver standing upon 

 the shelf. To know when these are level, 

 depress the receiver until the coloured fluid 

 in one leg of the bent tube, or inverted 

 syphon, 5, stands level with that in the other 

 leg, as at 6 ; then the water contained in the 

 receiver, and that external to it, are level to 

 each other ; and the air within the receiver is 

 of the same density as that without. 



Immediately the plug 15 is replaced, and 

 the hands withdrawn from the receiver, the 

 latter will be seen to ascend some half-inch, 

 the water behind the slip of glass to fall, and 

 the coloured fluid in the bent tube to be 

 unequal. This is caused by the excess of 

 weight in the counterbalance (1 1, 11,), which 

 is what necessitates the observation of the 

 coloured fluid in the bent tubes and the cor- 

 rection above directed. The scale is gra- 

 duated to degrees, each of which measures 

 two cubic inches. 



To correct the respired volume for tem- 

 perature. The table of the vital capacity- 

 volume is calculated at 60 Fahr. The tempe- 

 rature of a volume of air displaced out of the 

 lungs into the spirometer is reduced at once to 

 the temperature of the water in the spiro- 

 meter. This, according to the season of the 

 year, may be 50 or 80. Now 330 cubic 

 inches at 50 would occupy 337 cubic inches 

 at 60, and 330 at 80, would be 317 at 60. 

 For eight months out of the year there needs 

 no correction. But a correction is necessary, 

 when a thermometer in the room stands 

 much above or below 60. We may estimate 

 the change in the bulk of air as 7 Vo f r every 

 degree (Fahr.) of variation of temperature ; 

 thus if a man breathe, in winter, 295 cubic 

 inches of air into the spirometer, when the 

 thermometer in the room stands at 55, being 

 5 degrees below 60, then -^ = 2'95, must 

 be added to the 295 cubic inches, making 

 297'95, or, in round numbers, 298 cubic 

 inches. On the other hand, if the vital ca- 

 pacity be determined at 215 cubic inches, 

 when the thermometer stands at 72, which is 

 12 above 60, ^- = 5 must be deducted; 



making the corrected observation 210, instead 

 of 215 cubic inches. 



In the absence of the spirometer, the mea- 

 sure of the mobility of the ribs, by means 

 of a common tape measure is of much value.* 

 To measure the mobility of the thorax with 

 a tape measure, pass the tape measure round 

 the chest under the waistcoat, over the region 

 of the nipples, request the person to in- 

 spire deeply, and note that circumference, 

 then to expire deeply, and again note the 

 circumference, the difference is what we 

 term the mobility. This is a rough measure- 

 ment, but of no little value in doubtful 

 cases of chest disease. This difference, or 

 mobility, in men of all statures should be 

 about 3 inches, if it is found only 2i inches 

 the examination should be carried further ; 

 sometimes the mobility extends to 5 inches, 

 but this is excessively rare. As a general rule, 

 when we find the mobility three inches, we 

 find the vital capacity volume correspond with 

 our table. Sometimes the mobility may be 

 good, and the vital capacity bad, because, as 

 we have already noticed, we may move* the 

 walls of the chest without breathing. 



The vital capacity is a constant quantity ; 

 habit will not increase it. But this volume is 

 disturbed directly, and modified by five circum- 

 stances : 



1st, by height ; 2nd, by position ; 3rd, by 

 weight ; 4th, by age ; 5th, by disease. 



1st. Of the effect of height. 



The vital capacity volume bears a striking 

 relation to the height of the individual exa- 

 mined ; so that, if we take a man's height, we 

 can tell the volume of his vital capacity. We 

 show this by a curve in^/zg. 710., as before ; let 

 the perpendicular lines represent the heights 

 increasing inch by inch from the left towards 

 the right ; the single continuous line is the 

 curve of the vital capacity, which gradually 

 ascends as it passes over the perpendicular 

 lines. The heights extend from 5 feet to 6 feet ; 

 above six feet the observations are few. Whe- 

 ther the vital capacity volume maintains the 

 same regular progression beyond this point 

 remains to be determined. If we draw a line 

 in a perfect arithmetical ascent of eight units 

 for every increasing height, the line of vital 

 capacity will be observed to run nearly pa- 

 rallel with it; therefore this volume increases 

 with the increase of stature. The figures at 

 the bottom represent the vital capacity in 

 cubic inches, being the mean of the observa- 

 tions under each height. The following table 

 (TAIILE T.) places the subject more in 

 detail : 



A cursory inspection of the table shows 

 that the vital capacity increases with the 

 height ; this is without any consideration as 

 to age, weight, or circumference of the chest. 

 For clearness, we arrange it in a more re- 

 duced form, as in TAKLE U. 



* Dr. Sibson and Dr. Quain have invented some 

 ingenious instruments for measuring the thoracic 

 movements externally. 



