454 BAOTEBIOLOGY. 



the disease of animals known as anthrax represents a 

 type of the condition. If the cadaver of an animal 

 dead of anthrax be examined by bacteriological methods, 

 it will be discovered that there is present in all the 

 organs and tissues an organism, a bacillus, of definite 

 form and biological characteristics; and if the organs, 

 and tissues generally, be subjected to microscopic exam- 

 ination this same organism will be found always present 

 and always located within the capillaries. At many 

 points it will be seen crowded in the capillaries in such 

 numbers as almost, if not quite, to burst them, and very 

 commonly their lumen for a considerable extent is en- 

 tirely occluded by the growing bacilli. In such a case 

 as this we might be tempted to conclude that death had 

 resulted from mechanical interference with the capillary 

 circulation. Suppose, however, we subject the cultures 

 obtained from this animal to conditions, either chemical 

 or thermal, that are not particularly favorable to their 

 normal development, and from time to time inoculate 

 susceptible animals with the cultures so treated. The 

 result will be that, as we continue to expose our cultures 

 to unfavorable surroundings, the period of time that is 

 required for them to cause the death of animals will, 

 in some cases, gradually become extended, until finally 

 death will not ensue at all after inoculation. If, as 

 these animals die, a careful record of the conditions 

 found at autopsy be kept and compared, it will ulti- 

 mately be noticed that the animals that die a longer 

 time after inoculation present conditions more or less 

 at variance with those seen in the original animal that 

 died more quickly after having been inoculated. These 

 differences usually consist in a diminution of the num- 

 ber of bacilli that appear upon culture plates from the 



