32 



LECTURES ON BIOLOGY 



protoplasmic motion takes place in the interior of the cell : 

 slowly and lazily a short pseudopodium emerges here and there, 

 though the movements are as yet so slow that they are capable 

 of demonstration only by persistent observation. But the higher 

 the temperature rises the more active become the functions until 

 the maximum is reached at 26 C. If we now continue to 

 increase the temperature beyond that point we observe that a 

 retrogressive process is taking place : the protoplasmic motion 

 slows down, the pseudo-feet are retracted, the amoeba gradually 

 assumes its globular form, and when an upper limit of 35 C. 

 has been reached, become once more motionless ; it now lies in 

 a state of ' heat-coma.' 



6 



8 



FIG. 8. Amoeba Umax AT DIFFERENT TEMPERATURES. 



(1) In a state of chill-coma at + C. ; (2-8) the temperature is being gradually 

 increased ; (4) + 26 C., maximum of vital activity ; (8) in a state of heat-coma at 

 + 35C. 



Like warmth, the conditions of air and water pressure have 

 a far-reaching influence upon the normal course of life. Here, 

 too, there are upper and lower limits which may not be trans- 

 gressed except at peril to life. Unfortunately our knowledge 

 of the effects of increased or decreased air-pressure is as yet very 

 primitive, but the experience gained in various balloon ascents 

 is nevertheless of interest. It has been shown that it is impos- 

 sible, at any rate for a human-being, to ascend beyond a certain 



