388 AGRICULTURAL REPORT. 



Tliiei theory has some plausibility, in view of the fact that when acida are 

 aiWt'd to milk in suiiicieut quantity the casein separates — that is, the milk 

 curdles. So it does when by exposure to the air it becomes sour spontaneously, 

 which souring is due to the conversion of the lactose or milk sugar into lactic 

 acid. But the above statements are believed to have been made upon insuffi- 

 cient data, and to be inconsistent with other indubitable facts. Although it is 

 true that freshly drawn milk sometimes exhibits an akaline reaction, it is equally 

 true that it is sometimes neutral, and also that it often exhibits a decidedly acid 

 reaction. I have myself owned cows whose milk, when in perfect health and 

 in pasture, as soon as drawn, would distinctly redden litmus paper, and 1 have 

 known hundreds of others to do the same, thus showing an appreciable amount 

 of free acid when quite new ; nor did this milk curdle or become sensibly sour 

 sooner than other milk. 



If we are to accept theories based upon isolated facts, we might in this case 

 as well say that cream is held in solution by free acid, as in the other by free 

 alkali, but another view would account for its solution in a liquid perfectly 

 neutral. Again : if it were true that the casein of milk is held in solution by 

 virtue of a free alkali, it would be precipitated — that is, the milk would curdle 

 just as soon as this alkali was neutralized. If this were the case, newly drawn 

 milk would never present an acid reaction, for before this could be the case the 

 milk would be changed to curd in the udder, and could not be drawn from it. 

 Experience has demonstrated that whether the casein of the milk is separated 

 spontaneously in connexion with the development of lactic acid from the con- 

 version of milk sugar, or by the addition of other acids to the milk, as is prac- 

 ticed in some countries, good cheese is not the result. To this end the action 

 of rennet is indispensable — an action the precise nature of which is not known, 

 although it is probably what is cailed "catalytic," or an "action of presence," 

 a name given to an action which we know little about beyond the facts. That 

 the action of rennet in curdling milk is not due to the elFect of acid may be 

 easily demonstrated by any one who will take the trouble to test the fact as in- 

 dicated by the experiment alluded to in the next paragraph. 



Rennet is an infusion of animal membrane. Various membranes of different 

 animals will serve to curdle milk, but tlie stomach of the young sucking calf, 

 cleaned and salted, dried, and kept a year or more, is preferred to all others. 

 The infusion as usually prepared is slightly acid, but that it is not the acid in 

 it which effects the coagulation is shown by the fact that it may be made slightly 

 alkaline by the addition of potash or soda, and still be effective. Milk which 

 is slightly alkaline, I have found, may be curdled by rennet, which has jmrposel y 

 been rendered alkaline, and the whey jyfoduccd in such case skoived an alkaline 

 reaction, so that in cheese-making we may conclude that the coagulation is not 

 effected by means of acid, as many have taught. Be the explanation of the ac- 

 tion of the rennet what it may, we must, until better advised, be content to ac- 

 cept and act upon the facts as demonstrated by experience. The most impor- 

 tant of these facts are, first, that i*enuet curdles milk in-espective of acid; and 

 secondly, that the presence of lactic acid, from the conversion of milk sugar, 

 facilitates coagulation. 



In treating of the chemical composition of milk, casein is usually spoken of 

 as its only nitrogenous constituent ; but this is not correct, for milk contains 

 at least one, and perhaps two or more, other nitrogenous constituents besides 

 casein. Albumen is one. Its proportion is smaller than that of casein, being 

 usually from one-quarter to one-half of one per cent., but its existence may be 

 easily verified by taking a portion of whey rendered bright and clear by fitering, 

 and elevating its temperature. Before it reaches the boiling point the albumen 

 which was dissolved in it, and which resisted the action of the rennet, is co- 

 agulated by the heat applied, and separated in a flocculent mass. Its office as 

 a constituent of milk is uot fully understood, but it probably plays an important 



