96 THE CELL 



ture of 0, the protoplasm is found to exhibit an inclination to 

 break up into separate drops. Even where the network still per- 

 sists, it is composed of extremely fine threads, which are studded 

 here and there with large globules and drops ; several other glo- 

 bules float about freely in the cell fluid, in which, without moving 

 much from place to place, they revolve about their own axes with 

 active, jerking movements. After a few minutes, the free globules 

 are seen to unite themselves to the delicate threads, or to amalga- 

 mate themselves with some of the globules hanging on to the 

 threads, until the appearance of the streaming protoplasmic net- 

 work is quite restored." 



In plants, as a rule, their power of resistance to cold is inversely 



in proportion to the amount of water they contain ; seeds which 



| have dried in the air, and winter-buds, the cells of which consist 



almost entirely of pure protoplasm, can withstand intense cold, 



whilst young leaves, with their sap-containing cells, are killed 



/ even by frosty nights. However, the power of resistance to cold 



varies according to the specific organisation of different plants, or 



rather of their cells, as is proved by daily experience (Sachs IV. 



32B). 



Micro-organisms are able to resist exceedingly low tempera- 

 tures. Frisch has discovered that the spores, and indeed the 

 vegetative cells of the Anthrax bacillus do not lose their capacity of 

 development by being cooled down in a liquid to a temperature of 

 110 C., from which they were extracted after it had been thawed. 



Before reaching the above-mentioned extreme temperatures, at 

 which death by heat or cold is produced, phenomena known as heat 

 rigor or heat tetanus, and cold rigor, occur ; when the protoplasm 

 is in either of these conditions, all the atti'ibutes which show it to 

 be alive, especially those of movement, are arrested so long as 

 the temperature in question is maintained ; but when this is either 

 raised or lowered, as the case may be, after a period of rest, they 

 again manifest themselves. 



Cold rigor generally occurs at a temperature of about C., 

 whilst heat rigor sets in at a temperature only a few degrees lower 

 than that at which immediate death results; in both cases the 

 protoplasmic movements becomp gradually slower and slower, until 

 at last they quite cease. Amnebfe, Reticularia, and white blood 

 corpuscles draw in their pseudopodia and become converted into 

 globular masses. Most plant cells assume the appearance described 

 above by Kiihne. If the temperature is either slowly raised or 



