260 G. T. CALDWELL. 



Binney, the slimy salamander, Plethodon ghttinosns Green, the 

 cricket frog, Acris gryllus Le Conte, all hygrophilous animals. 

 The natural environments of these animals give a fairly wide 

 range of maximum evaporation. With the exception of Acris and 

 Tenebrio, the animals were kept in the laboratory only a few days 

 and in all cases were under as nearly natural conditions as 

 possible. 



III. METHODS OF DESICCATION AND CARBON DIOXIDE 



DETERMINATION. 



The desiccating apparatus consisted of a series of washing 

 bottles so arranged that air could be drawn through sulphuric 

 acid, granulated zinc, and glass wool into the desiccating chamber. 

 The air from the desiccator \vas bubbled through a methyl orange 

 solution for three hours to test for sulphuric acid. This test was 

 repeated at intervals throughout the work and at no time were 

 there indications of sulphuric acid in the air. 



The respiratory apparatus devised by Osterhout was used to 

 make the carbon dioxide determinations. Since this apparatus 

 has already been described (Osterhout, 1918), a brief summary 

 will suffice: the apparatus consists of a closed system in which air 

 is circulated by means of a pump. There are two possible ways 

 for the air to pass from the animal chamber, either directly into a 

 Pyrex glass tube containing an indicator solution, or indirectly 

 through a container of sodium hydroxide which removes the 

 carbon dioxide from the air before it reaches the indicator solution. 

 Thus, the desired color may be restored to the latter without the 

 necessity of a change of indicator. This is highly advantageous 

 because a series of determinations is possible without the admis- 

 sion of air to the closed system. In all experiments, 4 cc. of an 

 aqueous solution of phenolsulfonephthalein were iised. The 

 indicator solution was made at the beginning of each experiment 

 in sufficient quantity to last throughout one complete experi- 

 ment, except when the experiment ran for several days, which 

 occurred only in the woik on the larvae of Tenebrio and Alypia. 

 A north skylight lamp and a white background made of absorbent 

 cotton were employed to avoid the changeable color quality of 

 daylight and furnish a constant light for work at night upon tin: 



