Dynamic Theory. 

 such transformations are probably greater now than ever before. Bas- 

 tian's claim that he has been able constantly to evolve animal or fungus 

 vital organisms from mixtures containing vegetable infusions but desti- 

 tute of germs, is not at all unreasonable. But, on the other hand, in a 

 state of nature, new and unsettled forms of life, whether vegetable or 

 animal, have a much smaller chance for survival in the struggle for life 

 now than they would have had in the very early times, because there 

 are so many more higher organisms that depend on these lower ones for 

 their food supply, and, therefore, gobble them up as soon as formed. 



CHAPTER XXXI. 



ZYMOTIC AND GERM DISEASES. 



Modern discovery has established the fact that the animal body af- 

 fords very good conditions for the subsistence of hordes of invisible 

 parasitic organisms. No animal body, big or little, is exempt from con- 

 tributions levied by some of these organisms. The fact was suspected 

 by our ancestors before the use of the microscope had enabled them to 

 learn its true nature. They reasoned from what they could see with the 

 unaided eye. They could see insects. I believe it was Dean Swift who 

 formulated the idea thus : 



" Big fleas have little fleas, and these have less to hite 'em, 

 These lesser, have still smaller fleas, so on ad infinitum." 



The reality was much worse than they suspected. The terrible plagues 

 that devastated Europe during the middle ages, were due to parasites 

 far worse than fleas. The blood, lymph, and other rich juices of the 

 animal body, are as good food for the single celled bacteria, vibrios, mi- 

 crococci and such like, as they are for the cells of the legitimate tissues 

 of the body. When these adventitious germs enter the body, they 

 proceed to live on this food, and a struggle for life ensues between the 

 old settlers and the new comers. In some cases, however, there is 

 enough for all, and it often happens that we are the unsuspecting resi- 

 dences of tribes of bacteria on whose account we are apparently none the 

 worse. These presumably live on what the normal cells of our tissues 

 can spare ; in some cases, perhaps, on what they excrete. 



There are others which, by dint of numbers and insatiable greed, 

 consume so much of the food supply as to impoverish and starve the 

 normal tissue cells ; and others still which so destroy and pervert the 

 secretions and nutritive fluids, that they are no longer fit for the use of 

 the legitimate tissues. 



There is a certain degree of defmiteness and constancy in the organi- 



