H4 AIDS TO BACTERIOLOGY 



conjunctiva, is extremely like the diphtheria bacillus in 

 morphology and staining reaction, but it grows more 

 slowly, and the cultures are thinner, drier, and more 

 granular than those of the diphtheria bacillus, and it is 

 non-virulent. 



These organisms can be differentiated by fermentation 

 reactions. Buchanan obtained excellent results by 

 coagulating ox-serum in an equal quantity of water, 

 filtering the mixture, adding 1 per cent, of glucose to one- 

 half and 1 per cent, of saccharose to the other half, and 

 ' tubing,' neutral red being used as an indicator. In 

 twenty-four hours a marked acid reaction was produced 

 in the glucose tube by B. diphtheria, and in both tubes 

 by B. xerosis, while no change was produced in either 

 tube by the bacillus of Hofmann. 



Hiss's serum-water medium is also used for the fer- 

 mentation reactions: Serum 1 part, water 3 parts, with 1 

 per cent, of a carbohydrate or glycerin, tinged with litmus. 



The virulence of the bacillus varies considerably. The 

 average amount of a forty-eight hours' broth culture 

 required to kill a 250 to 300 gramme guinea-pig within 

 one to two days is 0-5 to TO c.c. 



Channels of Infection. Diphtheria is particularly a 

 disease of the young between the ages of two and ten; 

 the mortality is greatest at ages below five, and during 

 the last quarter, and is lowest during the summer months. 

 Its distribution is world-wide, but it is most prevalent 

 in cold and temperate climes. The ' school influence ' is 

 an undoubted factor in disseminating the disease, there 

 being a decrease in the number of cases during holidays. 

 The disease may be acquired by direct infection, as in 

 kissing, or by less direct means. The organism retains 

 its virulence for a long time in particles of dried mem- 

 brane, sputum, and discharges. As a rule, the bacilli 

 disappear from the throat within three or four weeks of 

 the beginning of the attack, but they often persist for 

 longer periods. Millard found bacilli present thirty days 

 after admission in 25 per cent, of his cases, and a case of 

 Hewlett's repeatedly gave the organism for twenty-two 

 weeks after the commencement of convalescence. A case 

 should not be pronounced as being free from infection 

 until at least two, preferably three, examinations have 

 shown that the bacilli are no longer present. 



