J0I1N£ OF AGRICDITIAL RESEARCH 



Vol. XVI Washington, D. C, January 20, 191 9 No. 3 



VARIATIONS AND MODE OF SECRETION OF MILK SOLIDS ^ 



By John W. Gowen ,^- 7 *^' 



Assistant Biologist, Biological Laboratory, Maine Agricultural Experiment Station ''"•^■r^ 



INTRODUCTION ^; 



The chief contributors to the subject of the physiology of milk forma- 

 tion in the mammary gland have chosen as the foundation for their 

 theories the grounds of analogy with the mode of formation of the secre- 

 tion in the two types of glands, sebaceous and salivary, and as positive 

 evidence have cited histological studies of the mammary tissue. On such 

 grounds the conclusions are likely to be weak. As yet there has been 

 little attempt to use the store of accurate mathematical data on the 

 composition and variation of the milk constituents for the analysis of 

 this problem. 



The investigation reported in this paper is an attempt to analyze the 

 variations and associations of the constituents of Holstein-Friesian milk 

 to furnish definite mathematical evidence bearing on the problem of the 

 kind of mechanism liberating these constituents to form the fluid known 

 as milk. The specific problems and the viewpoints taken in this paper 

 may be best understood by considering the natural divisions into which 

 milk secretion falls. The mammary functions may be divided into two 

 main divisions. The first of these has to do with the formation of the 

 materials of milk before the constituents are finally brought together as 

 milk. The second has to do with the release of the complete product, 

 milk. The first of these needs only concern us. This problem may be 

 again narrowed to exclude the genetic differences which most certainly 

 exist between individual cows. Given the constituents of cow's milk, 

 our problem is thus limited to the maimer in which these constituents are 

 released into the milk ducts. Is it through the secretory action of the 

 gland cells or is it through the destruction of the whole or a part of these 

 cells? Toward the analysis of this problem and related problems the 

 data on the variations and associations of the constituents of cow's milk 

 have been collected. The special problems bearing on the question will 

 be discussed in coimection with the data of the later sections of the paper. 



' Papers from the Biological Laboratory of the Maine Agricultural Station No. 121. This paper is the 

 fourth of a series of studies on milk now being conducted in the Biological Laboratory of the Maine Station. 



Journal of Agricultural Research, Vol. XVI, No. 3 



Washington, D. C. Jan. 20, 1919 



ay Key No. Me.-i4 



(79) 



