The first and in some respects the most efficient of these means is cold. The blood and the colloidal fluids remain in the aqueous condition when the body is exposed to cold at freezing-point. "At this same point all vital acts, excepting perhaps the motion of the heart" (it is Dr. Richardson, be it remembered, who thus uses the significant word "perhaps"), "may be temporarily arrested in an animal, and then some animals may continue apparently dead for long intervals of time, and may yet return to life under conditions favourable to recovery." Dr. Richardson gives a singular illustration of this, describing an experiment which must have appeared even more surprising to those who witnessed it than that in which the rabbit was restored to life. "In one of my lectures on death from cold," he says, "which I delivered in the winter session of 1867, some fish which during a hard frost had been frozen in a tank at Newcastle-on-Tyne, were sent up to me by rail. They were produced in the completely frozen state at the lecture, and by careful thawing many of them were restored to perfect life. At my Croomian lecture on muscular irritability after systemic death, a similar fact was illustrated from frogs." It would appear, indeed, that so far as cold-blooded animals are concerned, there is no recognisable limit to the time during which they may remain thus frozen yet afterwards recover. But, even in their case, much skill is required to make the recovery sure. "If in thawing them the utmost care is not taken to thaw gradually, and at a temperature always below the natural temperature of the living animal, the fluids will pass from the frozen state through the aqueous into the pectous so rapidly that death from pectous change will be pronounced without perceiving any intermediate or life stage at all." Naturally it is much more difficult to restore life in the case of warm-blooded animals. Indeed, Dr. Richardson remarks, that in the case of the more complex and differently shielded organs of warm-blooded animals, it is next to impossible to thaw equally and simultaneously all the colloidal fluids. "In very young animals it can be done. Young kittens, a day or two old, that have been drowned in ice-cold water, will recover after two hours' immersion almost to a certainty, if brought into dry air at a temperature of 98 degrees Fahrenheit. The gentlest motion of the body will be sufficient to re-start the respiration, and therewith the life."