by Julius H. Hess, M.D.
The term premature, in the precise meaning of the word, refers to those infants born before the end of the fortieth week of pregnancy, but in common usage it refers only to those infants who have undergone a gestation period of two hundred and sixty days or less, and so it may be understood that when the designation premature is used, it refers to those infants born three weeks or more before the usual termination of pregnancy.
There is another class of infants who may be considered in practically the same category as the prematures. These are the weaklings, infants born possibly at term, or nearly so, yet who have suffered more or less severely during their intra-uterine existence through factors which interfered with their nutrition and consequently their development. They are classed as congenitally diseased or debilitated.
In contrast to the prematures there are the full-term and mature infants. The full-term must be considered that one who is born at the completion of the normal period of two hundred eighty days of pregnancy. The mature infant is one possessed of all the faculties for extra-uterine existence and may be born before or at the expiration of normal gestation. Thus it may be seen that the functional and not the anatomical characteristics should decide maturity. While prematurity pertains to time and congenital disease or debility to function, the prematures do not need to be weaklings, whereas the full-terms may show evidence of congenital disease or debility.
The congenitally diseased are usually pale in appearance, thin, underweight, show a lack of cutaneous turgor, and have a low reactive capacity, suckle and drink poorly and have a tendency to restlessness, abnormal abdominal distension and dyspeptic stools. Not infrequently this class of infants fails to gain weight in a normal manner and, therefore, often require several weeks to regain their birth weight. This indicates functional incapacity even in the absence of demonstrable organic disease. This lack of functional development varies greatly with the individuals.
With reference to this class Jaschke  remarks that we should admit that vital debility must be designated as a congenital functional deformity which manifests itself chiefly in a deficient resistance or very low tolerance to the conditions and variations of the extra-uterine life. The debilitated infants react on one hand with symptoms of disease toward physiological stimulus, and on the other hand their well-being is unfavorably influenced by the slightest degree of over- or understimulation.
Many premature infants, not only have been born before full-term, but also have their physical development retarded by intrauterine disease and are below the average physical development for fetuses of a similar age.
It must be remembered that all infants born before the end of a normal term are born before the end of a full intra-uterine pregnancy, and consequently their organs are not fully developed. As a result they show certain definite body weaknesses, and a lack of resistance to the traumas of extra-uterine life. These are immature even though fully developed for their fetal age.
This, however, is only a relative body weakness in the absence of inherited constitutional debility and malformations.
It is also a fact that the younger the fetus when leaving the uterus, the greater are the difficulties to be overcome in the carrying out of the required body functions necessary to life and, therefore, the lower its vitality.
In a study of premature and congenitally debilitated infants at least two factors in the life history of the fetus must be considered:
1) The term of its intra-uterine life.
2) The state of its functional development at birth as evidenced by the presence or absence of inherited disease.
Congenital debility is dependent upon constitutional influences in the parents, and intercurrent disease during the term of pregnancy.
Notwithstanding the fact that both of the above factors must be given the most careful considerations, practically, in most instances, the influence of either factor on the extra-uterine life of the fetus in its early days cannot be definitely determined.
 Physiologie, Pflege und Ernährung des Neugeborenen. J. F. Bergman, 1917.