394 PHYSIOLOGY OF BACTERIA 



The causes of death by old age can be identified, partly 

 at least, with well-known causes. The reactions leading 

 to death by interface tension depression are quite 

 unknown. 



Death by light and by rays of shorter wave-length 

 has been shown to be due to a photochemical (or physical) 

 process. The reaction itself is unknown. 



Death by freezing is ordinarily a complication of 

 several factors, which cannot, as a rule, be separated. 

 Experiments on starvation also usually involves several 

 factors, only one of them being starvation proper, 

 while cold-shock and, perhaps, traces of poison, or 

 leaching out of cell constituents, may have a stronger 

 deleterious effect than starvation. Death by suffoca- 

 tion is nothing but a special case of starvation. 



