236 LABORATORY EXERCISES IN BACTERIOLOGY. 



that employed used as a control. A drop of one per cent, alcoholic solu- 

 tion of phenolphthalein should be used as an indicator, which when added 

 to the inoculated tube at once strikes the usual red color of an alkali. If 

 the medium was not exactly neutral to phenolphthalein when the organism 

 was introduced, the same amount of the indicator should be added to the 

 control tube and the intensity of color in the former compared with that 

 in the latter tube. 



Repeat with cultures of Micrococcus pyogenes, Bacillus subtilis, Bacillus 

 typhosus, Mycobacterium diphtheria, and Microspira comma. 



7. Alkaloidal Products. Among the products of bacterial activity there is 

 a large group (a) of basic nitrogenous bodies, known collectively as ptomaines, belonging 

 to the amines (U"~ H CH 3 )' as cadaverine (N(CH 2 ) 2 C 2 H 5 ,OH), sepsine and putrescine; 

 ammonium bases, as choline, neuridine, muscarine, etc. ; pyridine derivatives (derived 

 from pyridine, C 5 H 5 N), as collidine (C 8 H n N), indol (C 8 H 7 N), and skatol (C 9 H 9 N) ; 

 as well as amido-acids (as leucine, tyrosine, etc.), and others. 



The method of isolation of these bodies is for the most part too complex for 

 the limits of the present outline. Generally speaking, these are not the seriously 

 poisonous products of bacteria. 



(6) Toxalbumins. In this group occur a number of the essential toxins or poisons 

 of pathogenic bacteria, bacterioproteins (as the old form of tuberculin and mallein), 

 and bacteria plasmins (poisonous principles extracted from a number of pathogenic 

 organisms, as of cholera or typhoid fever, by pressure). The toxins or toxalbumins 

 proper are substances which may be precipitated as amorphous poisons from bouillon 

 cultures of various bacteria (as Mycobacterium diphtheria) by the ordinary albumin- 

 precipitating reagents, as by alcohol. These substances are extremely unstable and 

 easily destroyed by heat, chemicals, exposure to light, and other agencies. They 

 are the most important, from a pathogenic standpoint, of all the bacterial poisons 

 and are responsible for many of the specific symptoms of infectious diseases; and in 

 most cases are active in extremely small amounts. There is some belief that instead 

 of true albumins in these bodies, we are dealing only with certain unrecognized bodies 

 in the midst of the albumins of the medium carried down in precipitation. 



Bacterioproteins differ from these latter in that, aside from their smaller toxic 

 power, they are not altered by heat. 



8. Antitoxins. In this general connection should be mentioned, briefly because 

 of our meager knowledge of their nature, the protective substances which exist or are 

 developed in the fluids and tissues of the animal body influenced by an infection. 

 These, of course, are not substances to be regarded as direct bacterial products, but 

 for convenience may be considered here in outline. The protection or immunity 

 of an individual from infections depends either upon some mechanical protection 

 (as that of the skin and other protective coverings, or of phagocytosis) or upon certain 

 chemical antagonisms (as the acids or alkalies in the secretions with which the infection 

 is brought into relation, or the alexins and antitoxins). Alexins are protective sub- 

 stances naturally pre-existing in the fluids of the body (serum and lymph), supposed 

 to be derived from the leucocytes. They have not been isolated, but are known to 

 be very unstable to heat (55 C. or above) and sunlight. They possibly aid phago- 

 cytosis by killing bacteria, after which the leucocytes may more efficiently destroy 



