216 PHYSIOLOGY OF BACTERIA 



agents, and therefore, this is the optimum temperature. 

 If we heat still higher, growth will be more rapid at first, 

 but since the growth-agent deteriorates faster than it 

 can be built up again, the cell loses gradually its growth- 

 agent, and will finally work with a lower concentration 

 of this agent which means a decrease in the growth rate. 



We must expect, then, that there is a definite optimum 

 temperature of growth, and that above the optimum, 

 we find the Tammann principle (see p. 129) established, 

 most rapid growth at first, decreasing rapidly with time. 



The well known experiments of M. Ward (1895) with 

 B. ramosus are as beautiful a proof of the above deduc- 

 tions as we can imagine. He states : 



"At the optimum, it {B. ramosus) metabolizes and grows, and 

 respires etc. at its best; but at a higher temperature, it may grow 

 for a short time more rapidly, but sooner exhausts itself, and so pro- 

 duces a poorer crop in the end." 



In his summary, Ward says on page 462: 



"At the optimum temperature, the growth is very rapid, and lasts 

 for a long time, and the organism uses the materials to maximum 

 effect, and produces from them the maximum amount of its own 

 substance, in other words, the largest 'crop.' 



"At temperatures above the optimum, however, the growth, 

 though at first as rapid as at the optimum temperature, lasts for a 

 shorter and shorter time, according as the temperature is further 

 and further removed from the optimum; consequently the curve, 

 though equally steep in its steepest parts, begins to fall soon and 

 growth ceases sooner, and the crop obtained from the same amount 

 of original food material is smaller and smaller according as the 

 temperature is higher. At length, a temperature is reached where 

 the curve is infinitely short, i.e. no growth occurs at all. This 

 temperature is, however, about 39°C. and indicates the death 

 point." 



(p. 459) "The maximum temperature, therefore, is not a fixed 

 point, until we approach 39°C. to 40°C. beyond which no growth 

 seems possible; but it differs according to the length of time the 

 organism has been exposed to the high temperature. Thus it fre- 



