158 RECENT RESEARCHES 



found quite effective in invariably causing the reproduction of 

 the organism, and the generation of the original disease when 

 introduced into the bodies of healthy animals. 



Special organisms have recently been found connected with 

 glanders. Many other observers have at various times reported 

 the discovery of certain specific Bacteria which they have regarded 

 as the pathogenic element in the production of certain specific 

 diseases. This, however, can only be proved by demonstrating 

 that the organisms, when cultivated outside the animal body, are 

 capable of giving rise to such maladies ; and in many of these 

 observations, the deductions are so covered by inexact assertions 

 and improbable hypotheses, that it is impossible to draw any 

 definite conclusions from the observations. 



The next step in the study of Bacterial pathology w^as the 

 discovery, by Pasteur, of the possibility of modifying (by cultivation) 

 the potency of the Bacteria as agents of disease. This discovery 

 was made during investigations as to a disease of fowls, called 

 Chicken Cholera. This is a disease of extreme virulence, proving 

 rapidly fatal, and capable of being constantly induced by inocu- 

 lation of the smallest drop of the blood of a diseased fowl under 

 the skin of a healthy one, one attack, if recovered from, being 

 a permanent protection from subsequent attacks. It is proved to 

 be caused by a microscopic parasite which can be cultivated 

 outside the animal. 



If we take a fowl that has just died of Chicken Cholera, dip 

 the point of a glass rod into the blood, and touch with the charged 

 point a decoction of fowl broth which has been sterilised by being 

 heated up to about 240° F.; keeping the liquid at a temperature of 

 77° to 78° F., and taking care (as in Tyndall's experiments) to 

 prevent the entrance of atmospheric germs, in a short time, it 

 becomes turbid, and is seen under the microscope to be crowded 

 with minute Bacteria, shaped like the figure 8. If from this vessel 

 we take the smallest drop, and charge a second quantity of the 

 sterilised fowl-decoction, the same phenomenon is produced ; and 

 the same process may be repeated an unlimited number of times 

 with the same result. After two or three days the thickness of 

 the liquid disappears, and a sediment forms at the bottom ; this 

 denotes that the development of the Bacteria has ceased, and 



