462 Profs. Percy Frankland and Marshall Ward. 



August 4, where the filament grows from 10 /t to 652 p in length, at 

 21 23'7, with an average doubling period of about thirty-five 

 minutes, it can be translated as meaning that the number of bacilli 

 increased as follows : 



2 bacilli became 



4 at the end of the first 35 minutes. 



8 ,, second 



16 third 



32 ,, fourth ,, 



64 fifth 



128 ,, sixth ,, 



and so on, and we may assume that if the supply of food-material 

 could be kept constant, and no disturbing conditions set in, this would 

 go on. If it went on for only half a day twelve hours there 

 would be nearly 4,000,000 of the bacilli produced from the pair 

 started with above, and the filament would be nearly 40,000,000 ft in 

 length i.e., nearly 40 metres whence some idea may be obtained of 

 the energy of the growth on the one hand, and of the limits imposed 

 by the culture-drops on the other ; for if we take the size of a drop as 

 1 cubic mm., which is approximately the volume of a hanging drop 

 such as is used in the cultures, and remember that the bacilli in 

 question are about 1'75 p in diameter, it will be found that the above 

 length of 40 metres, nevertheless, has plenty of room in the drop, for 

 the filaments have a volume of only 96,250,000 cubic /* to pack away 

 in the 1,000,000,000 cubic /u. of the drop, so that we see the latter 

 could hold ten times the quantity. 



We are now in a position to resume the discussion of these growth- 

 curves in detail, and the action of temperature, &c., on this schizo- 

 mycete, with more hope of success. 



It is evident that the normal growth-curve is one which begins to 

 rise slowly, and gradually gets steeper and steeper, and then slowly 

 rises less and less rapidly until the end. This gives a curve like a 

 long drawn out _S~ . 



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 sooner, 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. 



