6 BULLETIN 106, U. S. DEPARTMENT OF AGRICULTURE. 



hard to the touch and contain no fluid. Encircling the base of each 

 nodule there usually appears a pale or bright vascular area, appar- 

 ently due to increased vascularity (which a histological examination 

 proves correct), thus giving the lesion the appearance of a minute 

 vesicle surrounded by a vascular girdle. The nodules are scattered 

 here and there, frequently along the floor of the vulva in the clitoral 

 region, but quite as often on the sides or the roof of the vulva. Except 

 for the nodules and the vascular girdle about the base of each, the 

 surface of the mucosa in the early stage is smooth, pale rose-colored, 

 and normal. There is no swelling, no inflammation, no discoloration 

 of the vulvar mucosa, and no mucous or muco-purulent discharge. 



Slowly and insidiously the disease spreads to individuals which 

 have hitherto escaped, so that the older the heifers in a herd the 

 larger the percentage which shows the evidences of the disease. 

 The rapidity and uniformity in the spread of the malady rests largely 

 upon environment. In the closely housed and much-handled heifer 

 calves in dairies usually more than 90 per cent show the disease at 

 4 months of age, and before they reach one year the visible infection 

 generally reaches 100 per cent, but if by any chance .an individual 

 escapes infection until breeding age the first service by the bull 

 conveys the disease. In heifer calves not kept in close or prolonged 

 contact with their dams or with older infected heifers, and not much 

 if at all handled by persons who are habitually in contact with dis- 

 eased animals, the infection spreads much more slowly. Thus we 

 have observed in a herd of pedigreed Herefords approximately but 

 50 per cent of infection in virgin heifers and heifer calves. After 

 birth these calves were allowed to go with their dams for a day or 

 two and were then permitted to suck twice daily, but otherwise were 

 kept separate from their dams or other older cattle. 



In experimental heifer calves we have kept individuals up to 6 

 months, and even to one year old, without any trace of the infection. 



The influence of environment upon the spread of the infection in 

 heifer calves is further exemplified by Table 1, wherein the 122 veal 

 heifers observed showed an average infection of 61 per cent. The 

 percentage of infection among these calves is markedly below the 

 average infection among heifer calves in eastern dairy herds of corre- 

 sponding ages. Western veal calves largely run at liberty in the 

 open, exposed to the infection from their dams but not from personal 

 handling or close crowding in stables. 



The number of the nodules generally increases slowly with the age 

 of the virgin heifer from the date of infection up to puberty or 

 estrum, when the increased vascularity and functional activity of 

 the genital tract apparently favors a more rapid multiplication of 

 the nodules and intensifies generally the symptoms of the malady, 

 but these in the virgin heifer rarely if ever attain that intensity 

 commonly seen after copulation. 



