230 HEAT AND PROTOPLASM [Cn.VIII 



Above this temperature, the rate of protoplasmic movement 

 rapidly decreases. 



That temperature influences the irritability of protoplasm 

 is demonstrated by many facts. Thus, STRASBURGER ('78, p. 

 611) found that, at a high temperature, the light attimement 

 of swarm-spores changes. For example, swarms of Haematococ- 

 cus and Ulothrix, which are phototactic, move at 30 C. from 

 the to the -t- side of the drop. LOEB ('90, p. 43) has 

 found that Prothesia larvae do not respond to light at a tem- 

 perature below + 13 C. Similarly, in respect to geotaxis, 

 SCHWARZ ('84, p. 69) found that Euglena did not respond 

 at below 5 to 6 C. So, too, CAMPBELL ('88, p. 130) has 

 shown that the response of muscles to electric stimulus varies 

 with the temperature. Thus, with the neck muscles of the 

 tortoise at 



NUMBER OF SHOCKS PER SECOND REQUIRED 

 TEMPERATURE. 



TO TETANIZE. 



4C. 



9C. 



21 C. 



28 C. 



1 

 5 



25 

 34 



isms of the experiment have been taken are, unfortunately, rarely given in 

 experiments on heat. From observations made by the Massachusetts State 

 Board of Health (Report on Water Supply and Sewage, 1890, Part I, p. 660), it 

 appears that the various ponds and reservoirs in the state, having a depth varying 

 from 19 to 5 metres, had a mean August (maximum) temperature ranging (in 

 the different ponds) from 24 to 21C. Various rivers, mostly not of mountain 

 origin, had, in 1887, a mean July (maximum) temperature, varying (in different 

 cases) from 26.5 to 24 C. Even in those ponds and streams in which the 

 surface temperature is over 25, a lower temperature can be found below the 

 surface. Thus, from the report referred to, it appears that, while at 3.3 metres 

 below the surface we have nearly the surface temperature, at 6.6 metres below 

 the surface, we find a decrease of 3 to 10, and at 10 metres a decrease of 

 from 9 to 17 below the surface temperature in different ponds. As for the sea, 

 the highest recorded surface temperature is about 32 C. (Red Sea, Gulf of 

 Mexico.) See A. AGASSIZ, "Three Cruises of the Blake," Bull. Mus. Comp. 

 Zool., XIV, p. 301. It would be a valuable piece of work to determine the 

 maximum summer temperature attained by the waters of shallow ponds, pools, 

 and marshes inhabited by organisms. 



