1210 



'Phis ]»i()i)i'rly lias rriidcrcd j)()ssil)l(' our ('X])('iiiii('ii1s on 

 llic xitrificalioii of colloids (Ijuyct, 1!).")7). We ])ro('('('d('d 

 ill llu' foUowin,!'' inaniicr: A drop of a ^)i)' /> i»-('larni solulioii 

 was ))iit, when still hoi, on a thin i;-lass support and s])r('ad 

 out so as to form a layer about 0.2 mm. thick. Tliis prepa- 

 ration was then immersed in liquid air. AVhen we took it 

 out, the u'elatin was vitrilied, as shown 1)\' its li-ansparency 

 when viewi'd ai>'ainst ordinary liiiht and its ()])acity Ix'tweon 

 crossed uicols. After ahout 10 seconds of exposure to 

 room temperature, the gelatin became opaque under ordi- 

 nary illumination and reestablished light l)etween crossed 

 iiicnls (devitrilication, r/. Fig. ,')0). This fundamental ex- 

 periment has been the starting point of all the investiga- 

 tions which we made on the vitrification of protoplasm. 



Fig. .'}(!. Vitrified ;iii(i dcvitiitied gelatin gels on glass sui)i)oits, plioto- 

 giaplied against a dark baekground. The figure on the left shows the vitri- 

 fied gelatin almost transparent; the figure on the right shows the same prepa- 

 ration after it has been warmed up and has become opacpie l).v devitrification 

 (crystallization). (Original, Luyet.) 



To sum up, the method of vitrification consists essen- 

 tially in immersing a thin film of the liquid to be treated 

 in a bath at a very low temperature. 



Vitrification is a process of quite a different nature than 

 that used in the refrigeration industry as ** rapid freez- 

 ing." When some hundred ])ounds of food are fi'ozen in 

 10 or 15 minutes, small ciystals are formed which cause 

 less damage within the tissues than larger crystals, as 

 those found in slower freezing, would. In vitrification one 

 aims at avoiding crystallization altogether and, to achieve 

 this, the cooling velocity should be about a thousand times 

 higher than in the industrial process. 



