64 The Biochemistry of Semen 



from right to left; then the motion was communicated to the whole 

 vermicule; and, in a short time, the progressive motion begun.' 



In the XlXth century, Prevost (1840), de Quatrefages (1853), 

 Mantegazza (1866), Schenk (1870) and others, experimented with 

 sperm exposed to temperatures ranging from 0° to -17°, but it 

 was not until 1938 when Jahnel proved that human spermatozoa 

 can resist the temperature of solid carbon dioxide (-79"), and Luyet 

 and Hodapp demonstrated that frog spermatozoa can survive the 

 temperature of liquid air (-192°), provided that they are mixed with 

 a concentrated solution of sucrose before immersion in liquid air. 



These and subsequent studies by other authors, including Shettles 

 (1940), Shaffner (1942), Hoagland and Pincus (1942) and Parkes 

 (1945) have provided further strong support for the general con- 

 clusion, elaborated in detail by Luyet and Gehenio (1940) in their 

 treatise on Life and Death at Low Temperatures, namely that sperma- 

 tozoa, not unlike certain bacteria and some flagellates, are remark- 

 ably resistant to low temperatures and on vitrification pass into a 

 reversible condition of complete inactivity and quiescence. This 

 was described by Becquerel as ia vie latente' and has been compared 

 to the behaviour of a watch which, though well wound, can be 

 brought to a sudden standstill by some braking mechanism; such a 

 watch will start of its own accord as soon as the brake is removed. 

 The main principle underlying Luyet's thesis is that cells such as 

 spermatozoa manage to survive at low temperatures if cooling is 

 effected so as to by-pass the crystallization zone, by carrying the cells 

 straight into the range of sub-freezing temperatures known as the 

 vitrification zone, where they assume the non-crystalline, glass-like, 

 or vitreous state. The passage on thawing from the vitreous state 

 equally deserves attention and is best achieved by rapid warming, 

 again to avoid the crystallization zone. When these precautions are 

 maintained, it is possible to prevent colloidal changes ordinarily 

 associated with freezing and ice-crystal formation, such as dena- 

 turation and coagulation of proteins, protoplasmic precipitation, 

 release of enzymes and structural disarrangement. In the opinion 

 of Becquerel (1936, 1938), the principal danger to the 'latent life' 

 of cells at low temperatures is the damage to cellular structure 

 which occurs in the freezing zone, caused by the separation of water 



