408 DISEASES OF THE BLOOD. 



it rei^roduces the clinical symptoms, and causes death more or less 

 rapidly, according to the dose injected. 



The virulence of cultures grown in defihrinated calf's blood seems 

 more intense, and Moussu has been able to reproduce the clinical form 

 of the disease by applying to the umbilical cord of a new-born animal a 

 pledget of cotton wool saturated with such a culture, and covering it with 

 a dressing. The germs of the disease are spread throughout the byres 

 through the medium of faeces. When the umbilical cord has become dry, 

 that is, after the third day, the application of virulent cultures to the 

 stump no longer causes infection. 



Pathogeny. The pathogeny of this septicaemia of calves and of new- 

 born animals is easy to explain. 



At birth the young animals fall on the litter, and the umbilical cord 

 becomes contaminated. The infective agent, finding an excellent culture 

 medium in the tissues of the cord, at once begins to develop, increases in 

 enormous numbers, steadily ascends along the cord, and sets up septi- 

 caemia. It grows in the gelatinous Wharton's jelly and in the fibrinous 

 plug closing the arteries and umbilical vein, and soon enters the true 

 circulation. Septicaemia is then fully established, general disturbance 

 sets in, and with it the diarrhoea by which it is externally indicated. 



It is important to remember, however, that infection occurs most 

 readily through the medium of the cord, and during the first few days 

 after birth : it may occasionally be brought about towards the eighth 

 or tenth day, when the shrivelled portion of the cord falls ; in this case 

 its entrance is effected through the little umbilical wound. 



Lesions. The lesions are sometimes so obscure that the practitioner 

 may hesitate to deliver an opinion. 



In acute cases, where death occurs in two or three days, or even in 

 ten to twelve hours, post-mortem examination reveals only increased 

 vascularity of the serous membranes — the peritoneum, pleura, peri- 

 cardium, etc. ; and it may be almost impossible to discover anything 

 abnormal in the cord, for although the clots closing the arteries and 

 veins are infected, they are neither separated from the walls of the 

 vessels nor broken up. 



On the surface of the urachus, at the base of the bladder, and in 

 the depths of the peritoneal folds supporting the allantoid arteries 

 (sometimes also the hepatic vein), unequivocal signs of local ascending 

 infection may, however, almost always be found, together with intense 

 injection of the capillaries, little haemorrhagic spots, and commencing 

 formation of false membranes, etc. 



The infection extends also by the lymphatic vessels contained in 

 these peritoneal folds, and finally attains the sublumbar region. 



When the disease develops less rapidly the peritoneal cavity 



