338 INFECTIVE DISEASES. 



are certainly by no means conclusive. It does not follow from these 

 experiments that the disease diphtheria naturally occurs in the 

 oat or that under ordinary circumstances cats may contract the 

 disease from the human subject ; but the experiments show that, 

 like' guinea-pigs and rabbits, cats are susceptible to the toxic effects 

 of the extremely poisonous principles developed during the growth 

 ■of LbfHer's bacillus. 



Milk Diphtheria. 



It has been shown that milk infected with diphtheria has been 

 "the cause of epidemics among the consumers ; there have also been 

 epidemics apparently associated with the milk supply, in which it 

 Jias not been possible to trace the source from which the milk was 

 infected. A difficulty in tracing the origin in no way excludes the 

 possibility of contamination from a human source. In the light of 

 recent researches we should expect that it would be easy to overlook 

 the source of the virus, if it be true that diphtheria may exist without 

 ^ny symptoms indicating its presence, and be unrecognised until the 

 throat has been examined for diphtheria bacilli. As this fact was 

 unknown until quite recently, the absence of an acknowledged 

 ■case of diphtheria was taken as evidence that no diphtheria existed, 

 and consequently that the milk must have been infected by a 

 ■diseased condition of the cow. Mr. Power, whose views upon milk 

 scarlatina have already been referred to, endeavoured to trace the 

 ■origin of a milk epidemic to the very common disease of " garget," 

 or mammary abscess. This idea may be dismissed without further 

 ■consideration ; but the theory of some disease existing in the cow 

 capable of producing diphtheria in man was resumed by Dr. 

 Cameron, who suggested that there might be an eruptive disease of 

 the teats producing diphtheria, and by Mr. Power, who supported the 

 theory in an investigation of a milk-diphtheria outbreak in 1886 

 .at Oamberley. Diphtheria in this case existed in the neighbourhood, 

 but as the source of human infection could not be traced, attention 

 was drawn to two cows in the herd which had recently calved, and 

 •especially to one with chapped teats. Following this line of inquiry, 

 Klein investigated the behaviour of milch cows to the diphtheria 

 bacillus. Two cows were injected subcutaneously under the skin of 

 the shoulder with a Pravaz' syringe filled with a sub-culture in broth. 

 There was a rise of temperature, and on the third day a painful 

 tumour, which enlarged to the size of a child's head. In about a 

 fortnight the tumour began to decrease, and ultimately one cow 



