THE CLASSIFICATION OF BACTERIA 39 



of course, a possibility, hut not a certainty. The one thing we can 

 probably safely assert is that there is no probability that any saprophytir 

 variety now existing can, under any possibility, develop into the now 

 recognized varieties of pathogenic bacteria. It is almost impossible to 

 conceive that any such variety should develop parasitic tendencies , under 

 exactly the same circumstances as those varieties which now produce 

 disease. 



The fact that the chief pathogenic varieties of bacteria, which excite 

 disease in man, seem to have retained for centuries their characteristics, 

 in no way proves that when placed under different conditions they would 

 remain stable. As already stated the characteristics of bacteria can be 

 radically altered, but they then lose those special traits which enable 

 them to excite disease and so cease to exist as parasites and if they 

 have lost the capacity to live as saprophytes they cease to exist alto- 

 gether. 



Attenuation. As just stated it is established that the great majority 

 of parasitic bacteria can be so altered by being grown outside the 

 body, and especially by being subjected to unfavorable conditions, 

 that they, while morphologically the same, lose their power of devel- 

 oping in the body and of producing specific poisons. When either or 

 both of these properties are partially destroyed they can usually be 

 redeveloped ; but when absolutely lost they probably cannot be. 



The recovery of toxin production is brought about by developing the 

 micro-organism for a considerable length of time under the conditions 

 best suited for it. The recovery of the ability to grow in the body of any 

 animal species is brought about by causing the germ to develop in a 

 series of animals of ths same species whose resistance has been over- 

 come by reducing their vitality through poisons, heat, cold, etc. Another 

 method is to accustom the micro-organism to the animal's body by 

 letting it remain surrounded by the animal fluids as it rests in a per- 

 vious capsule in the peritoneal cavity, or by growing it in unheated 

 fresh serum or blood media. 



Chemical Composition of Bacteria. Qualitatively considered, the 

 bodies of bacteria consist largely of water, salts, fats, and albuminous 

 substances. There are also present, in smaller quantities, extractive 

 substances soluble in alcohol and in ether. Special varieties contain 

 unusual substances, as wax and cellules? in tubercle bacilli. Bacteria 

 possess the capacity in a high degree of accommodating their chemical 

 composition to the variety of soil in which they are growing. The same 

 variety of bacteria thus varies greatly in the quantitative estimation of 

 its chemical constituents. Each variety yields proteid substances pecu- 

 liar to itself, as shown in the effects produced by animal inoculation. 

 At present we know but little concerning the differentiation of these 

 specific substances. This subject will be taken up in detail under 

 bacterial toxins, etc. According to Cramer many bacteria contain 

 amyloid substances which give a blue reaction with iodine. True cellu- 

 lose has been found in some bacteria, and also large quantities of a 

 gelatinous carbohydrate similar to hemicellulose have been obtained. 



