20, TEXT-BOOK OF BACTERIOLOGY. 



Thus we find anaerobic germs widely spread, and they are capa- 

 ble of developing in various places, from whence their lasting 

 forms — their spores — are communicated to the water, earth, etc., 

 in which they are almost always to be found. Our knowledge on 

 this interesting subject is still very imperfect. In making our ex- 

 periments, it is a diflQcult matter to exclude all oxygen, and thus 

 obtain a prime condition for the growth of anaerobic bacteria, for 

 which oxygen is positively a poison. 



A slight trace of it is sufficient not only to prevent them from 

 multiplying, but to even kill their germs, with the exception of 

 spores, in a short time. 



Lastly, must be mentioned the influence of light. While the 

 ordinary daylight is unimportant with regard to the development 

 of bacteria, sunlight has, according to the joint testimony of a 

 number of investigators (among whom may be mentioned Duclaux 

 and Arloing), a decidedly prejudicial, destructive effect upon the 

 most tenacious forms of micro-organisms. Anthrax spores, when 

 exposed to the direct rays of the sun for a few hours, lose their 

 power of development, and even before this they show unmistaka- 

 ble signs of a certain debility and diminution of vital power. 



V. PTOMAINES— DEVELOPMENT OF PIGMENT— FORMATION OF 

 GASES-PRODUCTION OP ODORS. 



When the bacteria have all that is necessary to their develop- 

 ment — an alkaline food solution, a suitable temperature, and favor- 

 able atmospheric conditions — they increase and flourish luxuri- 

 antly. Yet this has a definite limit. 



The vital action of the bacteria produces substances some of 

 which have a tendency to check their further development. 



It has been noticed, for example, that, earlier or later, the proc- 

 esses by which the micro-organisms bring about the formation of 

 butyric acid, lactic acid, etc., cease, in consequence of the accumu- 

 lation of the acids themselves. It has been further remarked 

 that the micro-organisms living in the human intestines decompose 

 their contents more and more, till they at length produce sub- 

 stances which, when chemically analyzed, display antiseptic quali- 

 ties which could not but be deleterious to bacterial life. Such 

 observations have led to a great number of thorough investiga- 

 tions in this direction, from which it has been discovered that the 

 powers of the bacteria in producing definite chemical substances 

 are great and varied. This can be demonstrated by adding a solu- 



