356 Proceedings of the Royal Physical Society. 



blood, fseces, etc., these should be cleared out by means of a 

 hot iron, and the cavity filled with gelatine or Plaster of 

 Paris before the part is allowed to thaw. 



If it is advisable to keep thick sections such as one-half of 

 a mesial section of a trunk, the displacement of the viscera 

 upon thawing can to a considerable extent be prevented by 

 passing long needles into the tissues in different directions. 

 By the plans above mentioned I have succeeded in preserving 

 a large number of frozen sections with very little displace- 

 ment of the parts. 



The tissues do not all freeze equally well. Muscular tissue 

 is the best ; fat never freezes so hard and firm. The nervous 

 centres can easily be frozen, but on thawing it cracks 

 apparently by spicules of ice. This, as is well known, ren- 

 dered the freezing method useless in the microscopic ex- 

 amination of the brain and spinal cord; but Dr D. J. 

 Hamilton has shown that by steeping the nervous tissue in a 

 solution of syrup this is prevented, probably by causing the 

 particles of ice to assume a granular instead of a spicular 

 form. 



XVIII. Notes of a Journey to Mexico in 1879-80. By 

 Patrick Geddes, Esq., F.Pt.S.E., Lecturer on Zoology 

 in the School of Medicine, and Demonstrator of Botany 

 in the University of Edinburgh. 



(Read 19th January 1881.) 



In this paper an account (which has been published in the 

 last Eeport of the British Association) was given of the 

 geology of the Valley of Mexico, of the author's palaeontolo- 

 gical excavations, and of his zoological and botanical collec- 

 tion.* 



* (1.) "Report of Committee, consisting of Dr Gamgee, Prof. Schafer, Prof. 

 Allman, and Mr Geddes, for conducting Palseontological and Zoological Re- 

 searches in Mexico " (Report Brit. Ass., 1880). 



(2.) "Notice of Crustaceans collected by P. Geddes, Esq., at Vera Cruz," 

 by E. J. Miers, F.L.S. (Journ. Linn. Soc. Zool., vol. xv., 1880). 



