662 CONDITIONS AFFECTING THE DEATH OF FUNGI. 



mode of action. Pasteur has only been able to give 

 a series of hypotheses, which at the most show how, 

 with the help of vague speculations, this ingenious in- 

 vestigator is able to obtain great experimental results. 



III. Means for Killing Bacteria. 



Means for The means which are suitable for the destruction of 



bacteria. the lower fungi have a special interest, because in the 

 practical work of disinfection the problem is usually how 

 to injure the infective agents so that they can no longer 

 grow and multiply even under the most favourable con- 

 ditions of existence. 

 c ?S nued i Death of the bacteria occurs in the first place when the 



withdrawal of 



nutriment. exhaustion of the nutrient materials, or the withdrawal 

 of some material important for life and the consequent 

 state of latent life, are continued for too long a time. 

 The death of the individuals ultimately follows the pre- 

 vention of their development, but the period of time at 

 which this effect is produced varies greatly according to 

 the resisting power of the individual species of bacteria. 

 The spores of bacilli are the most resistant, and may 

 probably survive in a latent state for hundreds of years; 

 non-spore-bearing bacilli and micrococci, and more espe- 

 cially numerous parasitic fungi, are the most sensitive 

 in this respect. 



Withdrawal The withdrawal of water plays a particularly impor- 

 tant part. This mode of destruction occurs very widely 

 in nature, and all those bacteria which do not form 

 resting spores die in a relatively short period of 

 time. The marked difference in the length of time 

 during which non-spore-bearing bacteria, and those pro- 

 vided with spores, can resist the action of drying is a 

 very useful criterion as to whether any doubtful morpho- 

 logical structure is, or is not, a spore (pp. 428 and 406). 

 Spirilla and some species of cocci (streptococci) appear to 

 be the most sensitive to drying. Differences also exist 

 between the resting forms of various species, but these 

 differences have not as yet been accurately made out. 



