718 DISTRIBUTION AND HABITAT OF THE BACTERIA. 



Seasonal onr country the summer is naturally the time of the year 

 es ' during which those parasites which require a high tem- 

 perature can most readily establish themselves on articles 

 of food ; further, on account of the presence of raw decay- 

 ing fruits autumn is a particularly favourable time for 

 contamination with numerous and different kinds of 

 bacteria, and it so happens that, at the same time of the 

 year, the various articles of food are exposed to greater 

 danger of contamination by the bacteria preserved in 

 the soil, because the latter are at that time readily 

 distributed owing to the formation of dust .on the sur- 

 face of the ground. This dust formation is in our 

 climate almost exclusively limited to the end of summer 

 and to autumn, because it is only then that a superficial 

 dry zone is constantly and for a considerable time pre- 

 sent. Hence we have various reasons for believing that 

 at a particular time of the year exceptionally large 

 numbers of bacteria are taken into the intestine with 

 the food, some of which perhaps produce ptomaines, and 

 thus possibly prepare the intestine for more severe 

 diseases, while others may penetrate as infective agents 

 into the predisposed intestinal tract. 



From what has been said, it is evident that articles of 

 food probably form such a marked factor in the spread of 

 the infective diseases that we must in future attempt to 

 gain a more accurate knowledge of this mode of infec- 

 tion. 



Bacteria in Numerous bacteria of all kinds are also frequently 

 present in the artificial surroundings of civilised man ; 

 thus the clothing is for the most part very rich in 

 living micro-organisms, which have reached it partly 

 from the surface of the body and the excreta, and partly 

 from without by the dust and rain. Washing clothing 

 is not uncommonly the means of transport of faculta- 

 tive and obligatory parasites ; such a role on the part 

 of clothes is well known in the case of those infective 

 diseases which are localised in the skin (e.g., small-pox), 



