62 Cramer and M'Call 



essential to have a balance which would indicate weiorhts of about half a 

 kilo (the weights of the animal chamber, absorption tubes, which were all 

 made of thin glass) accurately and rapidly to a milligramme. Such a 

 balance was obtained from Collot (Paris). It is capable of weighing a 

 kilo accurately to fractions of a milligramme, and by means of a damper 

 arrano^ement the weighing of the animal chamber can be carried out in 

 about two minutes. The observations on the respiratory exchange were 

 made in hourly periods from the third to the eighth hour after a meal. 



In a series of preliminary observations the conditions were established 

 under which it is possible to obtain, in the case of normal animals, constant 

 results which can serve as a standard. The animals, which were of 

 approximately the same age and weighed from 125 to 160 grammes, were 

 kept in the specially constructed metabolism cages devised by Schaf er (5), 

 in which the amount of food eaten by the animals can be accurately 

 determined. The animals were fed at reg-ular hours with weicfhed 

 quantities of bread and milk (equal parts). In the evening the food was 

 placed in the cages at 6 p.m. and removed at 8 p.m., when the amount of 

 food consumed was noted. Althouorh in the evenino: the animals were 

 allowed to eat ad libitum, the amount of food consumed varied only 

 within narrow limits from day to day. The animals were fed again in the 

 morning at 8.45 a.m., when 10 grammes of the bread-and-milk mixture 

 were offered to them, and the empty beakers were removed after an hour. 

 Observations on the gaseous metabolism were made only if the animals 

 had been kept for at least ten days under these conditions. The animals 

 rapidly became accustomed to the routine, and ate the food with avidity 

 when it was placed in the cages. The observations on the gaseous 

 metabolism were begun as a rule at 10.45 a.m. and lasted till 4.45 p.m. 

 Observations were made onl}' if the animals had completely eaten the 

 10 grammes of bread and milk within one hour, which they did almost 

 invariably. 



Under these conditions the period of observation begins with a 

 respiratory quotient of about 1 in the third hour after feeding (i.e. from 

 10.45 a.m. to 11.45 a.m.) and falls o-raduallv till in the eighth hour after 

 feeding it reaches a quotient of about 0"75. The observations were made 

 in a warm room, which could be kept at an even temperature not only 

 through the day but also throughout the whole year. The animals were 

 kept in an adjoining room at about the same temperature. 



The animals when in the respiration chamber remained quiet, and were 

 asleep during almost the entire period of observation, except during the 

 weighing at the end of each hourly period and during the last (eighth) 

 hour when, being hungry, they became slightly restless and began to move 

 about. The general condition of activity or inactivity of the animals 

 during the periods of observation was noted. The significance of this 

 point will be discussed below. 



When it was desired to induce experimental hyperthyroidism, dried 



