208 MICRO-ORGANISMS AND DISEASE. [CHAP. 



purpose enumerate all that is known already by direct experi- 

 ment, but will only limit myself to reference to the researches 

 of Schroter, Cohn, and Wernich on that group of micro- 

 organisms known as pigment bacteria, i.e. bacteria which 

 only under certain conditions, notably temperature and soil, 

 produce definite pigments (Cohn's Beitrdge zur Biologic d. 

 Pftansen) ; to those of Hansen (Carlsberg Laboratory) on 

 yeast ; to those of Neelsen on the bacilli producing the blue 

 colour of milk, the bacillus syncyanus (Beitr. zur Biol. d. 

 Pflanzen, iii. 2, p. 187) ; to the works of Toussaint, Pasteur, 

 Chauveau, Koch, and others on the bacillus anthracis; 

 Arloing, Thomas, and Cornevin on the bacillus of symptomatic 

 charbon ; of Koch on the bacillus of tuberculosis ; of Israel 

 on actinomyces, and many others ; and particularly would I 

 refer to the many valuable suggestions and considerations 

 expressed by v. Nageli in these respects in his book, Die 

 niederen Pilze, Miinchen, 1877 and 1882. 



While from these observations it would appear that both 

 septic and pathogenic micro-organisms are capable of suffering 

 some modifications in their morphological and physiological 

 behaviour, it is nevertheless still an open question whether 

 an organism which under ordinary conditions is only 

 associated with putrefactive changes in dead organic 

 material, and which cannot under these ordinary conditions 

 grow and multiply within the living body, can, under certain 

 extraordinary circumstances, become endowed with the 

 power of growing and multiplying within the body of a living 

 animal, creating there a pathological condition, inducing 

 there an infectious disease. 



Three distinct septic micro-organisms have, after numerous 

 experiments and careful observations, been mentioned, as 

 being capable when growing under certain extraordinary 

 conditions of assuming pathogenic properties. These three 



