12 THE ANATOMY OF INVERTEBRATED ANIMALS. 



satisfactorily attempted only in the lowest and simplest 

 forms. It appears that, in the dry state, these are able to 

 bear far greater extremes both of heat and cold than in the 

 moist condition. Thus Pasteur found that the spores of fungi, 

 when dry, could be exposed without destruction to a tem- 

 perature of 120-125 C. (248-257 Fahr.), while the same 

 spores, when moist, were all killed by exposure to 100 C. 

 (212 Fahr.). On the other hand, Cagniard de la Tour found 

 that dry yeast might be exposed to the extremely low tem- 

 perature of solid carbonic acid ( 60 C. or 76 Fahr.) with- 

 out being killed. In the moist state he found that it might 

 be frozen and cooled to 5 C. (23 Fahr.), but that it was 

 killed by lower temperatures. However, it is very desirable 

 that these experiments should be repeated, for Cohn's careful 

 observations on Bacteria show that, though they fall into a 

 state of torpidity, and, like yeast, lose all their powers of ex- 

 citing fermentation at, or near, the freezing-point of water, 

 they are not killed by exposure for five hours to a tempera- 

 ture below 10 C. (14 Fahr.), and, for some time, sinking 

 to 18 C. ( 0.4 Fahr.). Specimens of Spirillum volutans, 

 which had been cooled to this extent, began to move about 

 some little time after the ice containing them thawed. But 

 Cohn remarks that Euglenaz, which were frozen along with 

 them, were all killed and disorganized, and that the same fate 

 had befallen the higher Infusoria and Rotifera, with the ex- 

 ception of some encysted Vorticellce, in which the rhythmical 

 movements of the contractile vesicle showed that life was 

 preserved. 



Thus it would appear that the resistance of living matter 

 to cold depends greatly on the special form of that matter, 

 and that the limit of the Euglena, simple organism as it is, is 

 much higher than that of the Bacterium. 



Considerations of this kind throw some light upon the 

 apparently anomalous conditions under which "many of the 

 lower plants, such as Protococcus and the Diatomacece, and 

 some of the lower animals, such as the Radiolaria, are ob- 

 served to nourish. Protococcus has been found not only on 

 the snows of great heights in temperate latitudes, but cover- 

 ing- extensive areas of ice and snow in the Arctic regions, 

 where it must be exposed to extremely low temperatures 

 in the latter case for many months together ; while the Arctic 

 and Antarctic seas swarm with Diatomacece and Radiolaria. 

 It is on the Diatomacece, as Hooker has well shown, that all 

 surface-life in these regions ultimately depends ; and their enor- 



