340 THOMAS J. HELDT 



logical salt solution five to ten minutes after death. It may be 

 possible however, as Held ('95) has pointed out, that the tolu- 

 idin-blue or the methylene-blue (Dogiel) may fix, or partially fix, 

 the tissue put into it. 



Regarding the alterations which freezing produces in the smear 

 preparations, very much depends upon the conditions under 

 which the freezing occurs. The factors previously referred to 

 may be repeated, namely, the composition of the substance or 

 tissue in question, the thickness of the smear, the degree of 

 temperature reduction, the rapidity of the freezing, the surface 

 tension and other intrinsic forces of the individual elements of 

 the substance or tissue investigated (e.g., the forces of molecular 

 attraction, imbibition, osmosis, etc.), to say nothing of thawing 

 and fixation. These factors have been wholly or partially recog- 

 nized by all investigators of the phenomenon of freezing. 



The freezing of water has been sufficiently discussed. The 

 physico-chemical explanation of ice-formation, though of funda- 

 mental importance in the following considerations, are given in 

 detail by Quincke and so will be referred to here only as occa- 

 sion demands. 



The appearances observed in the freezing of egg-albumen are 

 concisely expressed in Molisch's following statement in which 

 he describes his microscopical findings for the freezing of a 2 

 per cent aqueous solution of gelatin: 



An zahlreichen Punkten tauchen unter Abscheidung von Luftblassen 

 rundliche Eismassen auf, die, der benachbarten Gelatinegallerte das 

 Wasser entziehend, sich rasch vergrossern und dabei die immer wasser- 

 armer werdende Gelatine ringsum zur Seite schieben, so das diese, wenn 

 die Eisbildung ihr Ende erreicht hat, als ein hoehst complicirtes Ma- 

 schenwerk zwischen den Eiskliimpchen ausgespannt erscheint. Die 

 urspriinglich homogene Gelatine ist nun in eine Art Schwamm unge- 

 wandelt, in welchem das hoehst complicirte Geriistwerke aus Gelatine, 

 die Hohlriiume aber aus Eis bestehen. 



Molisch's observations on frozen egg-white are similar to his 

 above observations on gelatin, excepting that in the case of the 

 egg-albumen the network disappears on thawing, while that pro- 

 duced in gelatin is quite permanent for some time. It is of inter- 

 est here to note that Ambronn ('91) in his study of frozen gelatin 

 and agar-agar states that the appearance of the fine network 



