GROUP OF THE CUTANEOUS SECRETIONS 



901 



cell from which they have been derived, but it seems scarcely necessary to make 

 this assumption, because such an investment might more easily result in conse- 

 quence of the molecular attraction of the fat for the neighboring protein particles. x 

 If milk is boiled, a "skin" is formed upon its surface, which consists of lactal- 

 bumin, casein and calcium salts. Furthermore, when exposed to the air, milk 

 undergoes a peculiar fermentation in consequence of the entrance of micro-organ- 

 isms, chief among which is the bacillus lacticus. Its reaction then changes to sour, 

 owing to the formation of lactic acid from lactose. Milk may also undergo 

 alcoholic fermentation. While this change is not easily effected by means of yeast 

 cells, it is readily brought about by fungoid growths. The milk-sugar is converted 

 into glucose and galactose and the latter into alcohol and carbonic acid. In this 

 way, such preparations as Koumiss and Kephir have been derived. The coagula- 

 tion bf milk is usually brought about by means of rennin, an enzyme contained in 

 the gastric juice of mammals. The clot, or curd, consists of casein and entangled 

 fat-droplets, while the fluid residue, or whey, embraces sugar, salts, albumin and a 

 newly-formed protein called whey-protein. 



The Composition of Milk. The formation of milk depends not 

 only upon the condition of the mother but also upon that of the infant. 

 A robust woman, especially a multipara, may yield a large enough 

 quantity to feed half a dozen infants, but naturally, the true physio- 

 logical measure is the amount which is required for the wellfare of a 

 single infant, weighing, say, 3000 to 3500 grams. These requirements 

 are compiled in the succeeding table : 



1 day 20 grams 



2 days 75 grams 



3 days 168 grams 



4 days 252 grams 



5 days 303 grams 



6 days . 353 grams 



7 days 367 grams 



2 weeks 472 grams 



3 weeks 512 grams 



4 weeks 512 grams 



5 weeks 577 grams 



6 weeks 613 grams 



7 weeks 691 grams 



A comparison of these data with those now following shows conclu- 

 sively that the average woman furnishes an ample supply of milk, 

 and that the quantity secreted increases steadily as demanded by the 

 growth of the infant, until about the 28th week, when its amount di- 

 minishes up to the end of the period of lactation. 



Required by infant 



Secreted by mother 



1 day . 20 grams 



2 days 97 grams 



3 days 211 grams 



4 days 326 grams 



5 days 364 grams 



6 days 402 grams 



7 days 478 grams 



1 week 502 grams 



1 Hammarsten, Lehrb. der physiol. Chemie, 1907, und Raudnitz, Ergebn. 

 der Physiol, ii, 1903. 



