354 Proceedings of the Royal Physical Society. 



sible, must be made. The tin case is then placed in a perfor- 

 ated wooden box containing the freezing mixture. The freez- 

 ing mixture should entirely surround the case in which the 

 animal is placed, and means should be adopted to allow of the 

 escape of the water formed in the freezing mixture. 



Snow and salt (2 to 1) make by far the best freezing mix- 

 ture for this purpose. If snow cannot be obtained ordinary 

 canal ice, well-pounded, should be used. Snow is much more 

 convenient than ice, considerable difficulty and waste attend- 

 ing the pounding of the ice sufficient fine. A considerable 

 mass of freezing mixture should be used, and, if kept in a cool 

 place, it will not be required to be renewed oftener than once 

 every twelve hours. A lower temperature is obtained if the 

 mixture be well stirred up every two or three hours. 



The temperature of the mixture should be taken occasion- 

 ally by inserting into it a thermometer protected by a metal 

 tube. A temperature of 10° Fahr. can easily be obtained in 

 this way, and with a considerable mass of snow and salt I 

 have repeatedly found it about 0° Fahr., although the mixture 

 had not been renewed or stirred up for twelve to fifteen hours 

 previously. 



Care must be taken that the brine does not come in con- 

 tact with the animal, as parts saturated with it are extremely 

 difficult to freeze. A small animal, such as a rat, can be 

 frozen in a few hours, but an animal as large as a man takes 

 four or five days. With large animals one is apt to be 

 deceived by the hardness of the superficial parts, as the 

 integument may be very hard while the viscera in the centre 

 of the trunk are still unfrozen. 



The sections are best made with a saw. I use a tenon-saw 

 with a movable back, unless the animal is very large, when 

 I employ a saw with two handles, its teeth arranged so as to 

 cut both ways. The cut surface of the sections are to be 

 washed with warm water to remove the saw dust, and the 

 surface carefully dried as a layer of ice tends to form rapidly 

 upon it. 



As soon as the surface of the section has been cleaned, a 

 tracing should be taken of it. This can best be done by 



