PREVENTIVE MEDICINE 271 



it would probably be safe to say that even tuberculosis takes a sec< <ml 

 place. In 1909 M'Fadyean and Stockman* had already proved 

 the existence of the disease on 55 farms distributed over 36 counties, 

 and at the present moment probably no single county in the British 

 Isles is free. 



The disease is naturally propagated by cattle but other animals 

 are susceptible, and it has been conveyed experimentally with result- 

 ing abortion to mares, ewes, goats, bitches and sows. The pos- 

 sibility of infection of the human female is to be borne in 

 mind, though no case of abortion due to this organism has hitherto 

 been described. Judging by serum reactions male and non-preg- 

 nant animals are as susceptible as pregnant females, though no 

 clinical symptoms of infection are shown. It occurs chiefly, but 

 by no means exclusively, among young cows. It was at one time 

 almost universally thought that infection took place in a passive 

 manner per vaginam by contact with the contaminated urinary 

 channel. The bull was also considered to be a frequent transmitter 

 in a mechanical manner. Though bulls can be infected by inject- 

 ing material into the preputial cavity and heifers can in the same 

 way be infected per vaginam, it is highly probable that infection as 

 a rule in natural cases occurs by ingestion of food and water 

 contaminated with the specific organism. 



Virulent material is practically confined to the uterus of infected 

 cows and therefore, as Stockman has pointed out, gross infection 

 of pastures or cow-sheds only takes place at or about the time of 

 abortion. Bang's bacillus is, however, capable of prolonged extra- 

 corporeal life, provided that it does not undergo desiccation. Thus 

 on pastures and in cow byres it may remain virulent for a consider- 

 able time, according to Stockman nine months or more. The virus 

 is abundant in uterine discharges, in the foetal envelopes and in the 

 aborted foetus, and consequently food, water, &c., contaminated 

 through these agencies may be the means of spreading the disease. 

 According to Schroeder and Cottonf the discharge from an aborted 

 cow is infective for 20 or 30 and in rare cases for 50 days. It 

 can be laid down as probable that infective material has been got 

 rid of from the genital organs at most two or three months after 

 abortion. Aborted cows may retain the organisms in their milk 

 for a long period (Zwick, Schroeder and Cotton) and thus act as 

 carriers. Of 150 cows in a herd Schroeder and CottonJ found 

 that 14 per cent, were passing abortion bacilli with their milk. 

 *Journ. Comp. Path., 1909, Vol. XXII., p. 264, Abs. 

 t/ottrn. Amer. Vet. Med. Assoc., Vol. L., p. 321. 

 $Journ. Amer. Vet. Med. Assoc., Vol. L., p. 321. 



