BUREAU OF ANIMAL INDUSTRY. 35 



investigations is the uncertainty with which a proper exposure can be 

 obtained for treated hogs and accompanying control animals. Sub- 

 cutaneous injections of apparently virulent pure cultures of hog- 

 cholera and swine-plague germs rarely produce anything more than a 

 local inflammatory condition. Attempts to produce disease by feed- 

 ing the viscera of hogs which have died of hog cholera or swine plague 

 have failed in all but one instance in our recent work at the station, 

 and, in the case of the exception, the disease was of a very mild 

 chronic character. It is quite possible to kill hogs by injecting 

 cultures directly into their circulation; but by this method death is 

 caused rather by a toxsemic overpowering of the entire organism than 

 by an affection at all resembling hog cholera or swine plague, and 

 hence it is questionable whether it can be used advisedly as a test for 

 any system of immunization. 



TETANUS. 



No cases of tetanus occurred at the station during the year. The 

 antitetanic serum which is prepared at the station is regularly and 

 successfully used to immunize all the animals which, owing to their 

 condition and the work in which they are engaged, are liable to 

 become affected with tetanus. The two horses which supply the 

 serum have gradually been worked up to a state where the one can 

 bear 1,200 cubic centimeters and the other 1,550 cubic centimeters of 

 tetanus toxine at a single injection. This toxine is so virulent that a 

 fraction of a drop on subcutaneous injection kills a guinea pig within 

 twenty-four hours. The antitetanic serum will be tested for its cura- 

 tive value as soon as an opportunity presents itself. 



A peculiar effect of the tetanic serum, when used in immunizing 

 doses, has been observed on some cattle. These cattle, within an 

 hour after receiving an injection of from 10 to 15 cubic centimeters 

 of the serum, begin to show edematous enlargements about the eyes, 

 lips, nose, vulva, and rectum. The parts at times swell enormously. 

 The intensely stretched skin over the vulva and rectum assumes a 

 glistening appearance and looks as if the extreme tension would cause 

 a rupture. At times the skin of the neck and abdomen is also affected 

 and is covered with elevations resembling the appearance present in 

 urticaria, or nettle rash. The symptoms disappear after ten or twelve 

 hours, and the recovery of the animal is complete. An effort has been 

 made to determine whether the swelling is due to the antitoxine of 

 tetanus or to something normally present in the blood serum of the 

 horses. The question has not been finally settled, and will receive 

 more attention in the future. 



TEXAS FEVER AND TICKS. 



Several minor investigations concerning Texas fever were under- 

 taken and are still in progress. Along with other work of this kind 

 a number of ticks were secured through the division of zoology from 

 different countries which are plagued with ticks and a disease similar 

 to or identical with Texas fever. These ticks from Egypt, Cape Col- 

 ony, Brazil, Australia, and the West Indies are now being cultivated 

 to obtain good specimens for study and comparison with the North 

 American tick, which acts as the transmitting agent of the infectious 

 material of Texas fever. 



Little or no progress has been made in the search for a reliable dip 

 to destroy ticks on cattle. A number of new dips have been tested 



