STUDIES OF TISSUES DURING LIFE. 265 



Paris. In the course of their studies upon the pleuro- 

 pneumonia of cattle, a disease in which all investigators 

 had hitherto failed to detect by either microscopic or 

 culture-methods any species of bacteria that might rea- 

 sonably be regarded as the causative agent, they detected 

 a group of bodies, apparently bacteria, of such infinitesi- 

 mally small dimensions as entirely to escape detection 

 by the usual methods of examination. 



The results of Nocard and Roux were obtained both 

 through the adoption of special methods of cultivation 

 and the use of very high amplifying powers for micro- 

 scopic examination. The method of cultivation was that 

 suggested in 1896 by Metehnikoff, Roux, and Salimbeni, 1 

 and is essentially as follows : very thin-walled, small 

 sacs of collodion are sterilized by steam, filled with 

 bouillon, inoculated with the exudate or tissue to be 

 tested, sealed with sterile collodion, and placed in the 

 abdominal cavity of an animal rabbit, guinea-pig, 

 chicken, dog, sheep, or calf, as the case may require. 

 The wall of the collodion sac is impermeable to bac- 

 teria or to leucocytes, but is an osmotic membrane 

 through which fluids and some of their dissolved 

 contents readily diffuse. This diffusion supplies the 

 bacteria within the sacs with such matters from the 

 living fluids of the animal as are apparently essential to 

 their development, while at the same time the bacteria 

 develop uninterruptedly, being protected by the collodion 

 membrane from the antagonistic action of the fixed and 

 wandering cells of the tissues. After a period of from a 

 few days to several months the animal is sacrificed, and 

 the sac removed from the peritoneal cavity and its con- 



1 Metehnikoff, Roux, and Salimbeni: Annales de 1'Institnt Pasteur, 

 1896, p. 257. 



