RELATION BETWEEN TEMPERATURE AND GROWTH 455 



is found that the variation from one to another acts as a 

 stimulus, and induces a transient retardation of growth. 



But this cause of disturbance is eliminated when the rise 

 of temperature is made gradual and continuous. In this 

 way, by taking a continuous record of growth under uniform 

 rise of temperature, a thermo-crescent curve is obtained, that 

 gives data from which the absolute values of growth at all 

 temperatures may be obtained. From this curve we are also 

 able to obtain an accurate determination of the optimum and 

 maximum points. 



The Method of Balance also affords us, by means of a 

 sharply defined turning point, an exact indication of the 

 optimum point. 



The optimum point is very definite, and under normal 

 conditions is always constant for a given species ; but just 

 as the death-point was found liable to be shifted under 

 abnormal external conditions, so the optimum point also is 

 apt to be transposed under similarly disturbing causes. 



That growth is a phenomenon of excitatory response is 

 demonstrated by the fact that the growth-rate is increased or 

 decreased at different temperatures, in proportion to the 

 excitability of the tissue at the same points, as indicated by 

 its contractile response. 



