APPARATUS AND METHODS USED IN THIS RESEARCH. 37 



sion or contraction of which compresses the air inside of the pneumo- 

 graph tube, thus transmitting, to a delicate tambour outside, a record 

 of the slightest motion of the cage resulting from the movements of the 

 infant. This method of obtaining a graphic record of the muscular 

 activity is shown in more detail in figure 5 (p. 57). 



While the general features of this apparatus have already been dis- 

 cussed in considerable detail, 1 with increased experience and with the 

 facilities for modifying the technique to suit the conditions to be met, 

 certain fundamentally important variations from the previously estab- 

 lished technique have been found necessary. In this type of respira- 

 tion apparatus the infant is lying in a crib inside of a small respiration 

 chamber constructed of galvanized iron or copper and 77 cm. long, 25 

 cm. deep, and 37 cm. wide. To insure temperature control, the whole 

 respiration chamber is surrounded by a water-jacket consisting of a 

 second shell of galvanized iron or copper with a space of 5 cm. 

 between the two shells. To withstand the pressure exerted by the 

 weight of water, the two walls are separated by brass studs at approxi- 

 mately 5.5 cm. from each other, distributed all over the respiration 

 chamber. This water jacket, which is filled with water to within a few 

 centimeters of the top, acts also as a seal when the cover is placed upon 

 the apparatus. Through this double-walled jacket pass the two pipes 

 for the ventilating air-current, a pipe communicating with the spiro- 

 meter or tension equalizer, a small pipe for the stethoscope tube, and a 

 small pipe to connect the pneumograph of the body-movement regis- 

 tering device with the tambour outside. In the cover of the chamber are 

 a window securely sealed and an opening for the air-thermometer. 



In discussing the details of this apparatus, it seems best to follow in 

 a general line the course of the ventilating air-current as shown in 

 figure 2, from the time it leaves the respiration chamber until it returns. 

 It should be stated at the outset that the general description of the 

 apparatus previously referred to 1 gives a number of details that we 

 can not enter into here, and that at this point we will discuss only such 

 modifications as are essential for the successful prosecution of experi- 

 ments with infants and small animals. 



Psychrometer. — The psychro meter is essential for indicating the degree 

 of moisture inside the respiration chamber. This is of value not only 

 for the comfort or discomfort of the infant, but also for computing the 

 amount of gas, particularly oxygen, inside the chamber at the end of 

 the experimental period, since for these computations an exact knowl- 

 edge of the water- vapor in the air is essential. 



Formerly in the large respiration chambers it was necessary to aspi- 

 rate a definite volume of air over pumice-stone drenched with sulphuric 

 acid and note the increase in weight. Experiments carried out more 



1 Benedict, loc. cil. 



