344 PATHOGENIC BACTERIA IN MILK 



Lastly, the virulence of toxin-free cultures of the bacillus, obtained 

 by growing the bacilli for twenty-four hours in broth containing i 

 per cent, of glucose was tested on a guinea-pig weighing 250 

 grammes, with the result that it killed at 0-2 c.c. 



Channels of Infection in Diphtheria 



What is the relationship of diphtheria in man to the milk 

 supply ? How does the milk supply become infected ? These 

 questions it is not possible at present to answer with any measure 

 of exactness. But a consideration of their subject-matter raises 

 several points concerning diphtheria, to which reference must here 

 be made. In the first place, it is now generally held that the B. 

 diphthericB has a comparatively wide distribution in nature. Whilst 

 it appears not to be conveyed by water, it is believed that certain 

 conditions of soil favour its growth as a saprophyte. But this is 

 not proved. Eyre states that several groups of bacilli, having 

 similarities to the diphtheria bacillus, may be present in milk, and 

 the only way in which they are to be differentiated is by biological 

 and pathogenetic characters.^ In the second place, it has been 

 proved that persons suffering from diphtheria are foci of infection. 

 The exact channels of infection differ under varying circumstances ; 

 but, in general, the source of infection is the throat and mouth of 

 the patient. Anything which comes into contact with the mucous 

 membrane becomes infected. Thus handkerchiefs, sweets, children's 

 toys, etc., may act as the vehicles of contagion. The mucus and 

 saliva may also be infective, and in speaking, kissing, coughing, or 

 expectorating, such mucus (probably rich in bacilli) may be dis- 

 seminated in very fine particles, and so carry the disease. It is by 

 such means that the disease is spread. Richardiere and Tollemer ' 

 and others have proved that the dust floating in the air of a 

 diphtheria ward may contain large numbers of diphtheria bacilli, 

 and in this way milk and other foods may become contaminated. 



There remains another characteristic which it is not unlikely 

 plays a significant part in the propagation of the disease from 

 person to person, and therefore may at any moment convey the 

 contagion to milk, and that is the long period during which the 

 human throat may remain infective. Professor Sims Woodhead 

 has recently stated that " the persistence of the diphtheria bacillus 

 for periods up to eight weeks is of very common occurrence 

 whether antitoxin be given or not ; indeed, the majority of cases 



^ Brit. Med. Jour.., 1900, vol. ii., p. 427. 



2 Gazette des Maladies Infantiles, 1899, No. 10. 



