EXPERIMENT STATION RECORD. 



Vol. XXIV. June, 1911. No. 7. 



Previous descriptions in these pages of the respiration calorimeter, 

 designed for studies in human nutrition under this Office, have shown 

 the develoj^ment of the apparatus as an instrument of precision and 

 brought out its application in studying the physiological processes of 

 nutrition. Eecently changes have been made which greatly sim- 

 plify and improve its operation, and it has been applied to a new line 

 of research in a quite distinct field, the possibilities of which can 

 be as yet only barely suggested. 



In moving the apparatus from JNIiddletown, Conn., where it was 

 originally constructed, it was necessary to dismantle and dissect 

 it quite completely, so that its erection in the laboratory provided for 

 it in the neAV building of the Department involved in large measure 

 its reconstruction in manj^ important details. In this reconstruction 

 the general plan and principles of the apparatus which had given 

 such good results were retained, but numerous improvements and 

 some new accessory apparatus were introduced which make for ease, 

 accuracy, and economy of ox)eration, and which are of interest to 

 those following the refinement of this method of investigation. 



As the apparatus is very complicated and technical, some knowledge 

 of its construction and the principles on which it operates is necessary 

 to a general understanding of the changes which have been made. It 

 will be recalled that the apparatus combines the features of a respi- 

 ration apparatus and a calorimeter. It consists in primary terms of 

 an air-tight and heat-tight chamber of suitable size to accommodate 

 a subject during an experiment, provided with devices for measur- 

 ing and recording the products of respiration and the heat liberated. 

 The apparatus is of the closed-circuit type, the same air being passed 

 through the respiration chamber continuously as a ventilating cur- 

 rent. The products of respiration, carbon dioxid and water, are ab- 

 sorbed in the course of the circuit, and oxygen is supplied to replace 

 that used up by the subject. 



The calorimeter features, by which the heat is determined which 

 the subject liberates as a result of the vital processes of the body or 

 of external muscular labor, call for the highest degree of refine- 

 ment. It is this heat measurement which enables the calculation of 

 the energy expended by the subject in various operations, the avail- 

 able energy of food, the conservation of energy in the human body, 

 and the efficiency of the body as a machine. The apparatus is, of 



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