386 BACTERIA IN INFECTIOUS DISEASES. 



tion ; while when the material inoculated did not 

 contain these bacilli or their spores, a negative 

 result was obtained. Thus, in several cases, ex- 

 periments were performed with the contents of a 

 scrofulous gland and with various other material 

 proved by examination to be free from bacilli, and 

 in no instance did tuberculosis follow. The posi- 

 tive results obtained by other experimenters with 

 non-tuberculous material are explained by the sup- 

 position that tubercle bacilli or their spores have 

 been introduced at the same time. It is evident 

 that this accidental inoculation would be very apt 

 to occur in laboratories where tuberculous animals 

 had been kept under observation, and especially 

 where proper precautions are not taken as regards 

 cleanliness of the cages in which animals are kept, 

 and the isolation of those which are subjected to 

 inoculation experiments. 



According to Koch, the tubercle bacillus is a 

 slender rod from a quarter to a half of the diameter 

 of a blood-corpuscle in length, and presents certain 

 distinctive characters as regards its behavior with 

 staining reagents. The various methods of stain- 

 ing this bacillus are given in 'PART THIRD of the 

 present volume. The bacilli are found in consider- 

 able numbers in tubercles of recent formation, 

 more especially at the border of the cheesy masses. 

 They are abundant in the giant-cells, and seem to 

 possess a special relation to these cells. They are 

 not so abundant in old tubercles, although they are 

 seldom entirely absent. By placing a small por- 



