xni PATHOGENIC BACTERIA IN MILK 225 



few occasions (see p. 78). Its isolation from milk is a / 

 difficult matter. The best method of examination is to take 

 advantage of the rapid growth of this bacillus on blood serum. \ 

 The milk is centrifugalised, and cultivations are made upon 

 blood-serum tubes from both the cream and the sediment. 

 Dilution is obtained by acting upon the same principle as 

 that used in brushing agar and gelatine plates. A little 

 sediment or cream is taken up by sterile platinum loop, 

 and is rubbed in close vertical lines over the surface of three 

 blood - serum tubes without recharging the loop. A large 

 number of blood-serum tubes should be inoculated from both 

 sediment and cream, incubated at 37 C., and examined after 

 20 to 24 hours. A careful microscopic examination must be 

 made of all colonies, avoiding those certainly not colonies of 

 the diphtheria bacillus. If bacilli morphologically resembling 

 this organism are found they must be subcultivated and 

 obtained in pure culture. A certain diagnosis of the pre- 

 sence of the diphtheria bacillus from milk cannot be made 

 from the morphological characters alone. The cultural char- 

 acteristics and, in particular, animal virulence must be ascer- 

 tained. 



The importance of this is exemplified by the fact that 

 several observers have recorded the presence in milk of bacilli 

 which morphologically resemble the diphtheria bacillus, but 

 which from their other characters are certainly not that 

 organism. For example, Eyre, 1 from five milk samples out 

 of a large number, isolated organisms morphologically closely 

 resembling diphtheria bacilli. None of them were capable of 

 initiating lesions in guinea-pigs resembling those produced by 

 B. diphtheriae. Their cultural characters also differentiated 

 them from that organism. Bergey 2 isolated a number of 

 organisms from milk, drawn direct from the udder of cows, 

 which morphologically resembled the diphtheria bacillus.. 

 They were non- pathogenic. He isolated three groups of 

 organisms, of which the first, in their morphological and 

 biological characters, very closely resembled B. diphtheriae. 

 They grew on blood serum in practically the same manner as 

 the diphtheria bacillus. 



1 Brit. Med. Journ., 1900, ii. p. 426. 

 2 Journ. of Medical Research, 1904, xi. p. 445. 



