DISEASES OF CATTLE 405 



Neb. E. S. Bui. 52, 63 and 77; New Hamp. E. S. Bui. 56; N. Dak. 

 E. S. Bui. 44 and 58; Ind. E. S. Cir. No. 3. 



Parasites Affecting Cattle: Special Rept. on Disease of Oattle 

 U. S. Dept. of Agr. ; Vir. A. E. S. Bui. 112 and 113 ; New Hamp. E. 

 S. Bui. 28; Okla. E. S. Bui. 53 and 72; Miss. E. S. Bui. 28; Vir. 

 E. S. Bui. 108, 109 and 114; Kan. E. S. Bui. 69, 86 and 136; La. 

 E. S. Bui. (second series) No. 2; S. Car. E. S. Bui. 142; U. S. Dept. 

 Agr. Div. of Ent. "Insect Life," Vol. IV. Nos. 9 and 10 ; Iowa Agr. 

 E. S. Bui. 116; Texas Agr. E. S. Bui. 12 and 18; S. Dak. E. S. Bui. 

 131; S. Car. E. S. Bui. 114; Neb. E. S. Bui. 74; Ark. E. S. Bui. 20; 

 Fla. E. S. Bui. 28; Kan. E. S. Press Bui. 30 and 118; U. S. Bureau 

 of Animal Ind. Bui. 127. 



DISEASES OF T frE SKIN. 



ITCHING PRURITIS. 



It is best to consider pruritis first as a distinct subject. It is not 

 a disease, only a sensation, and therefore a symptom. It is one of the 

 symptoms accompanying the majority of the diseases which we will 

 consider in this chapter. It is, then, a functional affection produced 

 by slight irritation from without or by an internal cause acting upon 

 the sensory nerves of the skin. Nothing characteristic is seen except 

 the secondary lesions, produced mechanically by scratching or 

 rubbing. 



There are various forms of itching, the result of specific skin dis- 

 eases, where the pruritis is a secondary symptom. In such cases it 

 should not be regarded as an independent affection. 



Causes. Many causes may induce the condition which we recog- 

 nize here as pruritis. The most common one is dirt on the skin, 

 resulting from insufficient care. If the ceiling of the stable is open, 

 so that dust and straw may fall down, the skin is irritated and pru- 

 ritis results. It also occurs in some forms of indigestion. The parts 

 of the body most exposed to this condition are the croup, the back, the 

 top of the neck, and the root of the tail. 



Another cause is found in affections of the liver and of the kid- 

 neys, when an increase of effete material has to be thrown off by the 

 skin. Morbid materials circulating in the blood may produce a tick- 

 ling or smarting sensation of the skin in their passage from the blood 

 to the free surface of the skin. Certain irritating substances when 

 eaten may be excreted by the skin, and coming thus in direct contact 

 with the sensory nerves produce itching, or may go further and cause 

 distinct inflammation of the skin. In another class of cases the pru- 

 ritis may be due to an atrophy, contraction, or hardening of the skin, 

 when the nerves become irritated by the pressure. These conditions 

 may be so slightly marked in a thick skin like that of the ox that they 

 can not be recognized. It is frequently noticed that cattle will rub 

 themselves as soon as they pass from the stable into the open air 

 changing from a warm to a cold atmosphere. Again, we may find an 

 animal which does all its rubbing in the stall. We may look for lice, 

 but fail to find them. These conditions are generally attributable to 

 high feeding and to too close confinement. They may be associated 



