314 HENRY H. DONALDSON 



All of the bones of each of the 106 skeletons have been 

 preserved. 



It may be noted in passing that bones are somewhat hygro- 

 scopic and the oven-dried weights are not maintained for any 

 length of time under usual laboratory conditions. 



As a rule, the bones of the rat thus macerated are not markedly 

 greasy and do not show evident fat. There were a few excep- 

 tions to this, however (nos. 50 and 66 in this series), but no 

 correlated peculiarities were observed in such skeletons. When 

 bones were heated to 96°C. for six days the glass weighing 

 bottles sometimes became cloudy on the inner surface. This 

 cloud formed a turbid mixture with water and w r as dissolved by 

 alcohol. In no case, however, did it amount to one-tenth of 1 

 per cent of the weight of the bones, but nevertheless a correction 

 was made for it. 



It may be of interest to note that several trials gave eleven 

 working hours as the time needed to prepare a skeleton — 

 including the fresh and room-dried weighings and the necessary 

 records. The weighings and the records for the oven-dried 

 material added two hours more, making a total of thirteen hours. 



For the preparation of the skeleton the freshly killed animal is 

 to be preferred. If, however, the material needs to be pre- 

 served, some tests show that either saturated salt solution (brine) 

 or 50 to 60 per cent alcohol may be used without introducing 

 any marked modification in the results. Formalin is to be 

 avoided, as the macerating fluid acts with great difficulty after 

 formalin preservation. 



