58 GASEOUS METABOLISM OF INFANTS. 



For the graphic record we have used extensively the simple Porter 

 kymograph manufactured by the Harvard Apparatus Company, the 

 most advantageous speed of rotation corresponding to one complete 

 revolution of the drum in about 30 minutes. 



It has been found desirable to precede the experiment with a test 

 of the sensitivity of the apparatus for giving a good graphic record of 

 the movements of the crib to make sure that the tambour rubber is 

 intact and that there is a reasonably constant tension upon the tambour. 

 For this purpose a weight is placed in the center of the crib approxi- 

 mately equivalent to the weight of the infant upon whom the observa- 

 tions are to be made. The tambour and pneumograph are then con- 

 nected as usual and the kymograph set in motion, the speed being the 

 same as that used in the experiment following. A 50-gram weight is 

 next dropped from a definite height (21 cm.) so as to strike the crib 

 a blow at a certain distance (32 cm.) from the knife-edge bearing upon 

 which the crib rests. This imparts a slight impulse to the whole 

 suspended system and a series of vibrations takes place. The ampli- 

 tude of the vibrations as well as the number of the vibrations which 

 continue after the first impulse indicate the sensitivity of the apparatus. 

 This test is of great significance, accompanying as it does the kymo- 

 graph record for each experiment and proving positively that the 

 recording apparatus is in excellent condition. It also gives a rough 

 estimate of the degree of muscular activity and the true value of the 

 magnitude of the excursions of the pointer as the result of any restless- 

 ness on the part of the infant. 



The tambour was usually adjusted in the observations with infants 

 so that the distance between the end of the writing point and the 

 center of the tambour rubber was 190 mm. and from the center of the 

 tambour to the fulcrum 25 mm. ; all of the magnifications were there- 

 fore on the same basis. The curves may be made to show motions 

 that would otherwise be imperceptible to the eye by altering the 

 magnitude of the multiplication and the sensitivity of the apparatus. 

 For example, it has frequently been observed with both dogs and 

 infants that when the animal or the infant is very quiet, even the slight 

 change in the center of gravity produced by the respiratory movement 

 has been sufficient to give a clear and regular record of the respiration- 

 rate. Ordinarily such a degree of sensitivity is not at all necessary 

 and is not regularly employed. 



A typical kymograph curve, which was obtained with D. M. on 

 March 26, 1913, is given in figure 6. This also shows a record of the 

 sensitivity test which preceded the experimental periods. The vibra- 

 tions of the crib after the weight had fallen are shown by typical curves 

 which gradually decrease; the small disturbances of the line following, 

 also resulting in curves, are due to the lifting of the weight. After the 

 first test, the speed of the kymograph was increased and three tests 

 were made at the higher rate of speed. 



