FERMENTS. 85 



but it is accomplished in the surrounding media instead of in 

 a receptacle provided for the purpose, an alimentary canal. 

 This is one instance of a type of digestion which I believe to 

 be universal in case of all unicellular animals and plants. 

 The formation of a stomach is a provision for the conserva- 

 tion of force, but it in no way changes the modus operandi 

 of the digestive function. 



Now, if I have been understood thus far, you will probably 

 be enabled to understand the import of certain experiments 

 which have seemed involved in mystery. I will again refer 

 to a series of experiments by Mr. Lister, mentioned in my 

 last lecture, in which he says that he tried a large number of 

 experiments in which he found unmistakably that "it re- 

 quired several drops of tap-water (London hydrant water), in 

 which there were bacteria termo, usually one, to two, or 

 three, in a drop, to start putrefaction in blood serum ; while 

 the least possible portion of putrefying blood (containing, 

 probably, no greater number of bacteria), would start it at 

 once." He wondered at this, and says that "it may be that 

 some substance adheres to the bacteria, or is present in the 

 portion of decomposing blood, that starts the decomposition ; 

 whereas, the bacteria washed with pure water are free from 

 this." 



In another paragraph, Mr. Lister, always close to the front 

 when searching for truth, strikes much nearer the mark. He 

 says : " Or again, it seems to me conceivable that the normal 

 serum may oppose an insuperable obstacle to the nutritive at- 

 tractions of an individual bacterium, but that this may be 

 overcome by the associated action of several of the organisms 

 in close proximity, after the analogy of the more energetic 

 operation of a concentrated solution of a chemical reagent. 

 But whatever be the explanation, the fact remains." In this 

 paragraph we find a close statement of what seems to me to 



