Abstract
1. This paper is Part I of a series dealing with the relation between the chemical composition of milk and the stability of the caseinate complex to ethanol (Part II), rennet (Part III) and heat (Part IV).2. A description is given of the milk samples, which were taken from herd bulk milk, from individual cows in different stages of lactation and also from cows with subclinical mastitis.3. The methods used to measure the stability of the caseinate complex to the three coagulating agents are described, together with the methods used to make a detailed chemical analysis of the milk samples.4. The chemical composition of the samples is given and also the relation between composition and stage of lactation, and the interrelations of the concentrations of certain milk constituents.The authors thank Miss M. H. King and Miss R. E. M. Stevenson for technical assistance, Mr N. H. Strachan and Mr R. C. Voss (West of Scotland Agricultural College) for the sodium and potassium determinations and Dr P. S. Blackburn for the differential cell counts and bacteriological examination of the milks.