The nerve cell just prior to sleep is still well capable of response to stimuli, although perhaps the threshold-value of the stimulus has become rather high, whereas after entrance upon sleep and continuance of sleep for several hours, and more, when all spur to the dissimilation process has been long withheld, the threshold-value of the sensory stimulus becomes enormously higher than before.
The fatty matter, however, it must be borne in mind, is the expression of dissimilation of the actual substance of the proteids of the tissues, not of the splitting up of proteids or other carbonaceous nourishment supplied to them.
There is close interconnexion between the two aspects of the double activity that in physiological theory constitute the chemical life of protoplasm, between dissimilation and assimilation.
Sumerian has a system of vowel harmony strikingly like that seen in all modern agglutinative languages, and it has also vocalic dissimilation similar to that found in modern Finnish and Esthonian.
Vocalic harmony is the internal bringing together of vowels of the same class for the sake of greater euphony, while vocalic dissimilation is the deliberate insertion of another class of vowels, in order to prevent the disagreeable monotony arising from too prolonged a vowel harmony.