170 DISEASES OF 



should be held by an assistant and the head kept steady 

 by another assistant, holding one ear with one hand, 

 and the nose with the other. The operator can now 

 run the hand back through the opening in the specu- 

 lum, and examine the teeth carefully. If ulceration has 

 progressed to any extent, he will feel the hollow space 

 (cavity) in the tooth, or perhaps between two teeth. 

 Having discovered this hollow space, the diagnosis is 

 certain. I shall not describe the methods of removal 

 of the remaining portion of the ulcerated tooth, as the 

 services of a skilled operator with complicated instru- 

 ments will in nearly every case be found necessary. If 

 an old horse is the subject of the disease, it is best that 

 he be destroyed. 



PARASITES. 



Parasites are living organisms that obtain their sub- 

 stance from the nutritious material contained in the 

 bodies of other living organisms. Some of the para- 

 sites are of a vegetable nature, as the fungus of the 

 ringworm, occurring on the skin of man and most of 

 the domestic animals. Many parasites belong to the 

 animal kingdom, as worms, ticks, lice, fleas and various 

 kinds of flies. Then again some of the most destruc- 

 tive parasites that infect man and animals are neither 

 vegetable nor animal, but seem to have a realm by 

 themselves, about midway between the vegetable and 

 animal kingdoms. To this class belong the various 

 species of bacteria and cocci that are the cause of 

 most of the infectious aud contageous diseases in man 

 and animals. 



We shall not attempt to describe this last class. For 



