The teats of milked and unmilked quarters of 6 cows were deliberately contaminated twice daily by immersion in a suspension of streptococci and staphylococci. Only the unmilked quarters became infected, 7 with Staphylococcus aureus and 3 with Streptococcus uberis. Neither previous infection with the same strain or a different strain of pathogen nor existing infection with Corynebacterium bovis appeared to influence the results.

The detergents sodium dodecyl sulphate and octyl phenoxy polyethoxyethanol interact with casein and cause dissociation of the high-molecular-weight casein aggregates. It is presumed that the detergent binds with hydrophobic regions in the casein molecule. The size of the complexes formed between detergents and αs1-casein, β-casein and κ-casein, as estimated by gel filtration and sedimentation velocity experiments, suggests that the caseins were complexed as monomers.

During gel filtration under non-reducing conditions, detergent-κ-casein complexes were separated from other major components because of their conversion through formation of disulphide bonds into high-molecular-weight aggregates. This reaction, which did not occur in sedimentation velocity experiments, was presumably facilitated by the changes in the equilibrium between the individual caseins during gel filtration.

Sedimentation velocity experiments showed that a ratio of about 40 detergent molecules to 1 casein molecule was required to give the smallest casein-detergent complex.

Previous work had shown that when milk is boiled in a climbing film evaporator a reaction occurs between the casein micelles and the fat globule membrane, probably at the liquid–gas interface. It now appears that the micelle–globule complex is formed by combination of the κ-casein components of the micelles and the membrane of the fat globule. The reaction is not significantly affected by increases in concentration of individual constituents, or by changes in temperature or pH.

The history of the milk before its concentration is an important factor in its subsequent behaviour. Thus, cooling and stirring of the milk during storage, as normally occurs in a bulk collection tank, promotes the reaction in the evaporator and, for some milks, is essential for starting the reaction.

A high retention of whey by curds made from the concentrated milks, diluted with water to their original volume before renneting, indicates that curd properties other than fat retention are also altered during concentration.