Haz JACQUES LOEB AND HARDOLPH WASTENEYS 
temperature of 39° indicates a cumulative effect of the different 
exposures to a higher temperature. In other words, each heating 
increased the immunity and this gain was not lost during one or 
two days. 
V. THEIMMUNITY TO A HIGH TEMPERATURE IF ONCE ACQUIRED 
IS KEPT FOR MORE THAN FOUR WEEKS 
In order to prove this, fish were put for various lengths of time 
into a thermostat at 27°, tested in regard to their immunity against 
high temperature and then put back into the cold room and tested 
again. A few examples will illustrate this. Five fish were immun- 
ized to a temperature of 39° by exposing them daily for a number 
of hours to an increasing temperature, until they could live in a 
temperature of 39°C. (in m/4 Ringer solution). The process of 
acclimatization extended over a period of twelve days (see pre- 
vious experiment). After this they were kept for eight days con- 
stantly at a temperature of from 10° to 14°C. On the eleventh day 
they were put suddenly into a temperature of 31° and the tempera- 
ture of the water in which they were, was brought, inside of two 
hours, to a temperature of 39°, and then keptatthisheight. A con- 
trol experiment was carried on simultaneously with fish taken from 
the same cold room, which had not been acclimated. The solu- 
tions used were m/4 Ringer. The control fish that had not been 
acclimated to high temperature were dead in one and a half hour 
when the temperature had reached 36°. The acclimated fish kept 
alive for over an hour at 39° when the experiment was discontinued. 
In eight days, therefore, the HE of the fish to high tem- 
perature had not diminished. 
Four lots of fish had been immunized to a temperature of 35° 
by keeping themtwenty-four ,thirty-two, forty and seventy-two 
hours respectively at a temperature of 27°. After this the fish 
were put into the cold room and kept there at a temperature rang- 
ing from 10° to 15°C., for twenty-eight days. They were then 
put into an m/4 Ringer solution at a temperature of 35°. Simul- 
taneously six fish of the same lot, which had not been immunized 
but kept in the cold room permanently, were put into the same 
temperature and the same solution. Four of the latter fish died 
