ellAXGEH IX THE SECEETIOX 45 



less tlian those of single animals, for all members of 

 the herd are not affected in the same degree and quite 

 often the animals react in opposite ways under the same 

 cireumstances so that these variations are, in part, equal- 

 ized after the milk has been mixed together. The larger 

 the herd, the smaller the i)robability of all its members 

 being influenced in tlie same way at the same time — ■ 

 and, therefore, the variations from the normal will be 

 so much less. For the same reason, the variations are 

 (•onsid('ral)ly less wlien the milk of several, but always 

 the same, herds, is mixed. 



So far as we know, there are no data in Denmark 

 concerning the limits of the comi)Osition of normal mar- 

 ket milk, and these arc not sufficiently established in 

 other places — yet it ma\- be assunictl that the si)ecific 

 gravity does not vary hcsyond 1.(129 to 1.034, the content 

 of solids not fat does not exceed S.() to S.S per cent., and 

 the fat varies from 12.75 to .'!.5 per cent."' " 



v. CHANGES IN THE SECRETION DURING 

 DISEASES OF THE UDDER 



Diseases of the udder that cause material changes in 

 tlic character and the coiiqiosition of the uddei- secretion 

 are: udder contusion, udder cedema, embolism and 

 thrombosis, mastitis, udder tuberculosis, udder actino- 

 myc'osis and tumors. 



1. Contusions of the udder and the teats which fre- 

 (juently are caused by cuffing and blows and by kicking 

 and trami)ing by other cows, etc., produce hipmorrhage 

 of th(> udder tissues, bloody serous infiltration, or, 

 possi])ly, death of the udder tissue. The changes in 



' .1rrse\- herds, eU'., not included. 



" The liguies given above rehite to Danish cattle, practically 

 all of which are i>f two lireeds which furnish milk containing- a 

 ninrii lower percentage of fat than is furnished by mo>t of the 

 herds ])rodncing- market milk in America. [L. P.] 



