18 THE GENERAL CHARACTERS OF CELLS, BY S. STRICKER. 



of heat by carbon is an independent power, dependent on the very 

 nature of its substance, but it is by no means a spontaneous power. 

 The analogy, however, has only a one-sided value, since, if the coal 

 is once burnt, it can generate no new active force; but the contractile 

 substance is capable of restitution. 



The movements of contractile substances may be altered, 

 accelerated, retarded, or altogether stopped, by external in- 

 fluences (stimuli), which may vary greatly in kind and degree. 



Amongst the known conditions that exert an influence on 

 the movements of protoplasm, we may enumerate the variation 

 of temperature. The oldest reference to this fact was made by 

 Weber,* when he said the movement of cilia could be accelerated 

 by warmth. Kuhnef also remarked that the motions of 

 amoebse could be arrested by iced water, but that on raising the 

 temperature they recommenced. 



Since Max SchultzeJ has made the warming of the slide an 

 important assistance in micro-physiological investigations, we 

 have learnt that the locomotive cells of warm-blooded animals 

 can maintain their movements for a long time, external to the 

 organism, if kept at the ordinary temperature of the animal 

 from which they have been taken. We are unable, however, 

 to give any precise statements possessing general application, 

 respecting the influence of temperature. 



Still, as a general rule, an exaltation of a few degrees above 

 the temperature at which the organisms customarily live, 

 accelerates their movements, whilst a corresponding depression 

 retards them. If the temperature exceed certain limits, how- 

 ever, their life is imperilled. The eggs of trout, for instance, 

 undergo segmentation capitally in iced water, but in a warm 

 room soon die. 



The influence of temperature on the movement of cells is a 

 point of particular interest in reference to their migration. 

 Max Schultze has demonstrated that the colourless corpuscles 



* Canstatt's Jahreslericht, 1847, p. 59. 

 t -Das Protoplasm. Leipzig, 1864. 

 | Sch ultze's Archiv, Band i. 

 Loc. cit. 



