THE CAUSE OF CHOLERA 93 



cannot be observed with the most powerful of microscopes, hence 

 is called an ultramicroscopic virus. 



We know that this virus is present, because blood taken from 

 an animal affected with cholera and passed through the very finest 

 filters, and proved to be absolutely free from hog-cholera bacillus 

 or other bacteria, will produce the disease in typical form in healthy 

 animals into which it has been injected. 



(3) In sick animals the lesions in the bowels give off large 

 amounts of this ultramicroscopic virus which pass out in the intes- 

 tinal contents or feces. 



(4) Large amounts of the virus are absorbed by the blood from 

 the intestines and carried through the blood-stream to the kid- 

 neys, and thence pass out with the urine, which is, accordingly, 

 infectious and capable of producing the disease in other healthy 

 animals. 



(5) The blood itself is especially dangerous, and is literally 

 swarming with infectious material; so much so that as small an 

 amount as a few drops of virulent blood is capable of producing 

 the most fatal and acute types of the disease within a week in 

 healthy animals. 



(6) Other discharges from the animal body are also carriers of 

 the infection — e. g., the saliva, milk, and sweat. The sticky exu- 

 date formed around the eyelids during the course of the disease is 

 also a carrier of the germs of infection. 



(7) The usual manner in which the hog-cholera virus enters 

 the body of its victims is through the mouth. It thus enters with 

 the food and drink, more frequently perhaps with the food. It is 

 quickly absorbed from the intestines and enters the blood, in this 

 way producing both a local and a general infection. The germs 

 which remain in the intestines produce the local lesions or ulcers. 



(8) The virus is also sometimes taken in through the nose, and 

 thus is first brought in contact with the respiratory tract. These 

 are the cases which show the severe lesions in the lungs and pleura. 

 Many of the cases showing severe lung lesions are the result of in- 

 fection of these organs through the blood-stream. 



(9) The virus is taken in much more frequently through the 

 mouth than through the nose. 



(10) The infection is carried from one farm to another most 



