Influence of Disease. 67 



and is divided into the lactation period and the dry period. Good 

 milk cows give milk on an average for 300 days. Cows which are 

 not bred again, or which cannot be impregnated, may have a con- 

 siderably longer lactation period. 



During estrum a considerable diminution of milk in quantity 

 and quality may be observed in cows. Sucking calves may at this 

 time become affected with digestive disturbances. Hittcher and 

 Neumann state that the quantity and the proportion of fat dimin- 

 ish, while the casein contents and the specific gravity of the milk 

 are increased. There are however no set influences in one and the 

 same animal, and still less so in different individuals. Sometimes 

 the quantity of milk even increases, and not infrequently the milk 

 becomes abnormally rich in fat (Martiny). Fascetti and Bertozzi 

 found diminished quantity, increased specific gravity, and in- 

 creased dry substance, which they supposed resulted from the in- 

 creased proteid contents, especially from the increase of fat. The 

 volatile fatty acids in the fat according to Nilsen are diminished, 

 and the degree of acidity of the milk is frequently increased (Mez- 

 ger). As a whole, however, the milk is not materially changed 

 (Weber). 



No observations have been made on the influence of coition 

 and the beginning of another pregnancy. However the milk of 

 cows far advanced in pregnancy frequently has a lower value. It 

 coagulates sometimes as early as in the sixth, seventh, or eighth 

 month of the gestation period. Finally it becomes slimy, yellow, 

 and shortly before the cow goes dry it shows a similarity to colos- 

 trum. The amount of phosphoric acid and lime, contrary to that 

 in colostrum immediately after calving, is diminished, and the 

 taste is bitter and rancid (Backhaus). 



If cows are spayed 5 to 6 weeks after calving the milk is 

 supposed to be richer in fat, casein, and ash. The lactation period 

 of such cows is considerably lengthened, according to Gouin ex- 

 tending to 6 years. Lajoux on the other hand states that in healthy 

 animals the quality of the milk remains the same, but during the 

 course of lactation the cows do not dry off so rapidly and the yield 

 is therefore greater. 



Milk which is produced after abortion is supposed to be sim- 

 ilar to that of ripe milk (Schaffer and Hess). The lactation period 

 however is short, and the milk yield small. 



If the cow remains farrow for a long time a greater yield is 

 obtained. This however is only slight, and does not compensate for 

 the shrinkage during the latter part of the milking period. 



Influence of Diseases. 



Relatively little is known of the chemical changes which 

 milk undergoes from the influence of general affections of ani- 

 mals. We are in possession of better information relative to the 



