The Influence of Extraneous Factors 63 



motility at 45° (Amantea and Krzyszkowsky, 1921; Walton, 1930). 

 Cooling to a temperature just above 0° is not harmful to ejaculated 

 semen in vitro, provided however, that the temperature of the 

 ejaculate has been lowered gradually, preferably by successive 

 stages of 5°, with an interval of 2 hr. or so, between each. Sudden 

 cooling of ejaculated semen produces so-called temperature shock 

 and involves rapid and irreversible loss of motility and fertilizing 

 power (Gladcinova, 1937; Chang and Walton, 1940; Easley, Mayer 

 and Bogart, 1942). The decline of respiration and fructolysis in 

 'temperature-shocked' samples of bull semen was shown to be cor- 

 related with a proportionate increase of dead, that is eosin-staining, 

 sperm cells (Hancock, 1952). 



Provided that strict precautions are observed, semen can be cooled 

 well below 0° without destroying the sperm. Some of the earliest 

 observations concerning the effect of low temperature on sperm 

 (human, bull, stallion, and frog) were made by Spallanzani (1776, 

 1799). On subjecting stallion spermatozoa 'to the cold of freezing, 

 by putting the glass in which they were, among snow' he made the 

 following observations: 



'The same effect was produced by snow, as by the winter's cold; 

 that is, in fourteen minutes, it made the spermatozoa motionless; 

 although when exposed to the heat of the atmosphere, they con- 

 tinued to move seven hours and a half. But an accident that hap- 

 pened in this experiment, executed during summer, afforded new 

 intelligence, and divested me of a prejudice. Observing that the 

 vermiculi had become motionless, I took the glass from the snow, 

 and left it exposed to the air, when the heat was 27°. An hour after, 

 by chance observing this semen with the microscope, I was astonished 

 to find all the vermiculi reanimated, and in such a manner, as if 

 they had just come from the seminal vessels. I then saw, that the 

 cold had not killed them, but had reduced them to a state of com- 

 plete inaction. I replaced them in the snow, and in three quarters of 

 an hour took them away. These are the phenomena I observed. In 

 a few minutes, their vivacity relaxed, and the diminution increased, 

 until they lost the progressive motion, and retained only that of oscil- 

 lation, which likewise ended in a few minutes more. Exactly the 

 reverse was observed, when they passed from the cold of the snow to 

 the heat of the atmosphere. The first motion that appeared, was 

 that of oscillation; the body and the tail begun to vibrate languidly 



