302 RESPIRATION. 



poses, viz., for the appreciation of the relative and absolute 

 duration of the respiratory acts, and for the measurement of 

 their extent. For the latter purpose, the instrument must be 

 graduated every time that it is used. To facilitate this pro- 

 cess, I employ a set of five standard wooden measures of 

 length, differing from each other by two millimetres. With 

 these, the graduation is effected in less than five minutes. The 

 recording and receiving tympana having been brought into 

 communication, and the whole system tested as regards the 

 perfection of the joints, and found to be air-tight, one of the 

 wands (the one of which the length is equal to the mean of the 

 five) is placed between the two buttons of the stcthometer, 

 which are then approximated until the India-rubber membrane 

 of the tympanum is slightly concave. A horizontal tracing 

 having been drawn on the cylinder, the two next longest and 

 shortest wands are substituted for the first, and the process is 

 repented in respect of each, and then the next two, until five 

 parallel horizontal lines have been drawn, by comparison with 

 which, the variations of the diameters investigated may be 

 estimated in millimetres from the vertical measurements of the 

 tracings. By this method we learn, for example, that in a 

 healthy muscular young man, aged 22, the diameters above 

 given vary respectively in each respiration as follows : Upper 

 sternal diameter = 146, varies one millimetre; the lower ster- 

 nal diaineter=203, varies 1.5 1.8 millimetre; the transverse 

 costal diameter=228, varies 1.7 2.0 millimetres. 



As regards the duration and succession of the respiratory 

 acts, the most instructive curves are the costal and lower 

 sternal (see fig. 248). It must be carefully borne in mind 

 that the}' apply strictly to natural respiration. In forced 

 breathing, the thoracic movements acquire a different char- 

 acter. Dr. Arthur Ransome, who has studied the subject 

 with great accuracy, allows me to refer to his measurements. 

 He has found that the variations of the antero-posterior diame- 

 ters of the upper part of the chest are very extensive, and 

 that the whole thoracic framework participates in them the 

 ends of the upper ribs moving horizontally forward, i. e., in a 

 plane parallel to the middle plane of the body, from 12 to 30 

 millimetres ; the advance of the third rib is greater, by 

 several millimetres, than that of the fifth. Dr. Ransome con- 

 siders that this advance cannot be otherwise accounted for 

 than by an actual bending of the ribs. 



We shall see afterwards that the difference between natural, 

 and forced breathing consists partly in increased constriction 

 of the chest during expiration, partly in increased expansion 

 during inspiration. In the meantime, it is sufficient to note 

 that when the thoracic movements become excessive, the 

 change affects the antero-posterior diameters of the upper part 



