CHANGES IN THE SECEETION 45 



less than 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 

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

 ized after the milk has been mixed together. The larger 

 the herd, the smaller the probability of all its members 

 being influenced in the 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 

 considerably less when 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 composition of normal mar- 

 ket milk, and these are not sufficiently established in 

 other places — yet it may be assumed that the specific 

 gravity does not vary beyond 1.029 to 1.034, the content 

 of solids not fat does not exceed 8.6 to 8.8 per cent., and 

 the fat varies from 2.75 to 3.5 per cent.^ ® 



v. CHANGES IN THE SECRETION DURING 

 DISEASES OF THE UDDER 



Diseases of the udder that cause material changes in 

 the character and the composition of the udder secretion 

 are: udder contusion, udder oedema, embolism and 

 thrombosis, mastitis, udder tuberculosis, udder actino- 

 mycosis and tumors. 



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

 quently are caused by cuffing and blows and by kicking 

 and tramping by other cows, etc., produce haemorrhage 

 of the udder tissues, bloody serous infiltration, or, 

 possibly, death of the udder tissue. The changes ia 



' Jersey herds, etc., not included. 



° The figures given above relate to Danish cattle, practically 

 all of which are of two breeds which furnish milk containing a 

 much lower percentage of fat than is furnished by most of the 

 herds producing market milk in America. [L. P.] 



